阅读说明：本技术 辐射发射器、发射装置及其制造方法和相关的显示屏 (Radiation emitter, emitting device, manufacturing method thereof and related display screen ) 是由 W·S·谭 P·吕埃达·丰塞卡 P·吉莱 于 2019-02-06 设计创作，主要内容包括：本发明涉及适于发射第一辐射的发射器(25),包括至少两个这种发射器的发射装置(15),和用于制造其的方法。所述发射器(25)包括：-基板(55),-由具有第一带隙值的第一半导体材料制成的台面(40),所述台面具有上表面(70)和侧面(75),-覆盖层(45),包括由第二半导体材料制成的至少一个辐射发射层(85),所述第二半导体材料具有严格小于所述第一带隙值的第二带隙值,至少一个辐射发射层(85)具有对应于上表面(70)的第一部分(95)和对应于侧面(75)的第二部分(100),针对第一部分(95)定义了第一厚度(e1),以及针对第二部分(100)定义了第二厚度(e2),第二厚度(e2)严格小于第一厚度(e1)。(The invention relates to an emitter (25) adapted to emit a first radiation, an emitting device (15) comprising at least two such emitters, and a method for manufacturing the same. The transmitter (25) comprises: -a substrate (55), -a mesa (40) made of a first semiconductor material having a first band gap value, the mesa having an upper surface (70) and side faces (75), -a cover layer (45) comprising at least one radiation emitting layer (85) made of a second semiconductor material having a second band gap value strictly smaller than the first band gap value, the at least one radiation emitting layer (85) having a first portion (95) corresponding to the upper surface (70) and a second portion (100) corresponding to the side faces (75), a first thickness (e1) being defined for the first portion (95) and a second thickness (e2) being defined for the second portion (100), the second thickness (e2) being strictly smaller than the first thickness (e 1).)

1. An emitter (25) adapted to emit first radiation, the emitter (25) comprising:

-a substrate (55),

-a mesa (40), the mesa (40) being made of a first semiconductor material having a first bandgap value, the mesa (40) having an upper surface (70) and side faces (75), the side faces (75) surrounding the upper surface (70) and extending between the substrate (55) and the upper surface (70),

-a cover layer (45) comprising one or more radiation emitting layers (85), at least one radiation emitting layer (85) being made of a second semiconductor material having a second band gap value strictly smaller than the first band gap value, each radiation emitting layer (85) having a first portion (95) corresponding to the upper surface (70) and a second portion (100) corresponding to the lateral surface (75), a first thickness (e1) being defined for the first portion (95) and a second thickness (e2) being defined for the second portion (100), the second thickness (e2) being strictly smaller than the first thickness (e 1).

2. The transmitter of claim 1, wherein at least one of the following characteristics is satisfied:

-a first portion (95) at least partially covering the upper surface (70) of the table top, and a second portion (100) at least partially covering the side surface (75) of the table top (40);

-the second part (100) forms at least one quantum well, and

the side face (75) comprises a plurality of planes.

3. The transmitter of claim 1 or 2, wherein at least one of the following characteristics is satisfied:

-the substrate (55) is made of a semiconductor material, the mesa (40) extends from the substrate (55) along a first direction (D) perpendicular to the substrate (55) and is electrically connected to the substrate (55), the substrate (55) having a main surface (65) surrounding the mesa (40) in a plane perpendicular to the first direction (D), the substrate (55) further comprising an electrically insulating layer (60) extending over the main surface (65), the insulating layer (60) forming a potential barrier between the substrate (55) and the cover layer (45), and

-for each point of the side (75), an axis (a) is defined corresponding to a direction passing through the point and perpendicular to the side (75), and wherein the angle (a) between the first direction (D) perpendicular to the substrate (55) and the axis (a) is 30-80 degrees.

4. A transmitter according to any of claims 1-3, wherein at least one of the following properties is fulfilled:

at least one of the first semiconductor material and the second semiconductor material is a group III nitride material, and

-defining for the first semiconductor material a crystalline structure having at least one polar direction and at least one semipolar direction, the upper surface (70) being perpendicular to the polar axis, defining for each point of the lateral surface (75) an axis corresponding to a direction passing through said point and perpendicular to the lateral surface (75), said axis (a) being perpendicular to said semipolar direction.

5. The transmitter according to any of claims 1-4, wherein at least one of the following properties is fulfilled:

-the emitter (25) further comprises a first electrical contact (50) electrically connected to the first portion (95), the emitter (25) being configured to emit a first radiation when a current flows through the first electrical contact (50), the cover layer (45) and the mesa (40), the first electrical contact (50) being further electrically connected to the second portion (100);

-the emitter (25) further comprises a first electrical contact (50) electrically connected to the first portion (95), the emitter (25) being configured to emit a first radiation when a current flows through the first electrical contact (50), the cover layer (45) and the mesa (40), the first electrical contact (50) comprising a first connection layer and a second barrier layer, the second barrier layer being interposed between the first connection layer and the cover layer (45), the first connection layer being made of a fourth material, the fourth material being a conductive material or a semiconductive material, the second barrier layer being made of an insulating material, the cover layer (45), the second barrier layer and the first connection layer forming a tunnel junction;

-the capping layer (45) comprises at least two superposed radiation emitting layers (85) made of a second semiconductor material, a first barrier layer (90) made of a third semiconductor material having a third band gap value strictly greater than the second band gap value being interposed between each pair of successive radiation emitting layers (85), and

-the first radiation comprises a first set of electromagnetic waves, the radiation emitting layer (85) is configured to emit second radiation comprising a second set of electromagnetic waves, the emitter (25) further comprises a radiation converter (52) configured to absorb the second radiation and to emit in response to the first radiation, a wavelength is defined for each electromagnetic wave, the first set of electromagnetic waves corresponds to a first wavelength range, the second set of electromagnetic waves corresponds to a second wavelength range, the first wavelength range has a first average wavelength, and the second wavelength range has a second average wavelength, the first average wavelength is different from the second average wavelength.

6. The transmitter according to any of claims 1-5, wherein at least one of the following properties is fulfilled:

-the ratio of the first thickness (e1) to the second thickness (e2) is 1.5-6;

-the mesa (40) has a minimum transverse dimension (l) and a height (h), the height (h) being measured in a first direction (D) perpendicular to the substrate (55) and the minimum transverse dimension (l) being measured in a plane perpendicular to the first direction (D), the height (h) being strictly smaller than the minimum transverse dimension (l);

-the mesa (40) forms a frustum with a base (80) in contact with the substrate (55), the base (80) being rectangular or hexagonal;

-the mesa (40) has a height (h) measured in a first direction (D) perpendicular to the substrate (55), the height (h) being 100-1000 nm, and

-the upper surface (70) has a surface of 9-900 square microns.

7. Emitter according to any of the claims 1-6, wherein for each point of the side (75) an axis (A) is defined which corresponds to a direction through the point and perpendicular to the side (75), and wherein the angle (a) between the first direction (D) perpendicular to the substrate (55) and the axis (A) is 55-65 degrees.

8. A transmitting device (15) comprising at least two transmitters (25) according to any one of claims 1-7.

9. A display screen (10) comprising a set of emitting devices (15) according to claim 8.

10. A method of manufacturing an emitter (25) adapted to emit first radiation, the method comprising the steps of:

-providing a substrate (55),

-creating a mesa (40) of a first semiconductor material having a first bandgap value, the mesa (40) having an upper surface (70) and a side surface (75), the side surface (75) surrounding the upper surface (70) and extending between the substrate (55) and the upper surface (70), and

-depositing a cover layer (45) comprising one or more radiation emitting layers (85) on the mesa (40), at least one radiation emitting layer (85) being made of a second semiconductor material having a second band gap value strictly smaller than the first band gap value, each radiation emitting layer (85) having a first portion (95) corresponding to the upper surface (70) and a second portion (100) corresponding to the lateral surface (75), a first thickness (e1) being defined for the first portion (95), a second thickness (e2) being defined for the second portion (100), the second thickness (e2) being strictly smaller than the first thickness (e 1).

11. The method of claim 10, wherein the step for creating a mesa (40) comprises etching away a portion of a block made of the first material to create a mesa (40).

12. A method of manufacturing a transmitting device (15) comprising a first transmitter (25) and at least one second transmitter (25), each transmitter (25) being adapted to transmit a respective first radiation, the method comprising the steps of:

-providing a substrate (55),

-creating for each emitter (25) a mesa (40) of a first semiconductor material having a first bandgap value, the mesa (40) having an upper surface (70) and side surfaces (75), the side surfaces (75) surrounding the upper surface (70) and extending between the substrate (40) and the upper surface (75), and

-depositing on each mesa (40) a covering layer (45) comprising one or more radiation emitting layers (85), at least one radiation emitting layer (85) being made of a second semiconductor material having a second band gap value strictly smaller than the first band gap value, each radiation emitting layer (85) having a first portion (95) corresponding to the upper surface (70) and a second portion (100) corresponding to the lateral surface (75), a first thickness (e1) being defined for the first portion (95), a second thickness (e2) being defined for the second portion (100), the second thickness (e2) being strictly smaller than the first thickness (e 1).

13. The method of claim 12, wherein the step for creating each mesa (40) includes etching away a portion of a block made of the first material to create each mesa (40).

14. The method according to claim 11 or 13, wherein the mass is a baseplate (55).

15. The method according to claim 11 or 13, wherein the mass is a layer made of the first material and supported by a substrate (55).

Technical Field

The present invention relates to a transmitter. The invention also relates to a transmitting device comprising at least two such transmitters. The invention also relates to a display screen comprising a set of such emitting devices. The invention also relates to a method of manufacturing such a transmitter.

Background

The light emitting structure includes a stack of stacked semiconductor layers configured to form a set of individual light emitting mesas. Such structures are typically fabricated by etching away a portion of a stack of two-dimensional layers to define the light emitting mesa. Light emission is provided by a light emitting layer, typically located at or near the top of the mesa.

Such a structure allows easy control of the emission of each mesa, since the light emitting mesas are separated from each other, since each mesa can be independently powered, thereby reducing the risk of current leakage to adjacent mesas. Due to the above-mentioned advantages it has been suggested to use such a light-emitting structure as part of a display screen, each mesa forming a pixel if the screen is a monochrome screen or a sub-pixel if the screen is a multi-color screen. The spatial resolution of such a display screen is therefore directly related to the lateral dimension of the table top.

However, the exposed side of the mesa leads to increased surface recombination of the carrier. Thus, the overall luminous efficiency (also referred to as "electro-optical conversion efficiency") of such a structure decreases with the lateral dimension of the mesa, since the reduced lateral dimension results in a relative increase of the surface of the lateral side with respect to the surface of the light-emitting layer. As a result, the electro-optic conversion efficiency of mesa-based pixels or display screens may decrease as screen resolution increases, particularly when the lateral dimensions of the mesa are on the order of 10 micrometers (μm) or less.

Therefore, there is a need for a light emitter having a small lateral dimension and having high electrical-to-optical conversion efficiency.

Disclosure of Invention

To this end, the invention relates to an emitter adapted to emit a first radiation, said emitter comprising:

-a substrate

-a mesa made of a first semiconductor material having a first bandgap value, the mesa having an upper surface and sides surrounding the upper surface and extending between the substrate and the upper surface,

-a cover layer comprising one or more radiation emitting layers, at least one radiation emitting layer being made of a second semiconductor material having a second band gap value being strictly smaller than the first band gap value, each radiation emitting layer having a first portion corresponding to an upper surface and a second portion corresponding to a lateral surface, a first thickness being defined for the first portion and a second thickness being defined for the second portion, the second thickness being strictly smaller than the first thickness.

According to a particular embodiment, the emitter comprises one or more of the following features, taken alone or according to any possible combination:

-at least one of the following properties is satisfied:

a first portion at least partially covering the upper surface of the mesa and a second portion at least partially covering the side surfaces of the mesa;

the second part forms at least one quantum well, and

the side surface comprises a plurality of planes.

-at least one of the following properties is satisfied:

the substrate is made of a semiconductor material, the mesa extends from the substrate in a first direction perpendicular to the substrate and is electrically connected to the substrate, the substrate having a main surface surrounding the mesa in a plane perpendicular to the first direction, the substrate further comprising an electrically insulating layer extending over the main surface, the insulating layer forming a potential barrier between the substrate and the cover layer, and

for each point of the side, an axis is defined corresponding to a direction passing through the point and perpendicular to the side, and wherein the angle between the first direction perpendicular to the substrate and said axis is between 3 and 80 degrees.

-at least one of the following properties is satisfied:

at least one of the first semiconductor material and the second semiconductor material is a group III nitride material, and

a crystal structure is defined for the first semiconductor material, said crystal structure having at least one polar direction and at least one semipolar direction, the upper surface being perpendicular to the polar axis, an axis corresponding to a direction passing through said point and perpendicular to said side surface being defined for each point of the side surface, said axis being perpendicular to said semipolar direction.

-at least one of the following properties is satisfied:

the transmitter further comprises a first electrical contact electrically connected to the first part, the transmitter being configured to emit a first radiation when a current flows through the first electrical contact, the cover layer and the mesa, the first electrical contact further being electrically connected to the second part;

the emitter further comprises a first electrical contact electrically connected to the first portion, the emitter being configured to emit a first radiation when a current flows through the first electrical contact, the cover layer and the mesa, the first electrical contact comprising a first connection layer and a second barrier layer, the second barrier layer being interposed between the first connection layer and the cover layer, the first connection layer being made of a fourth material, the fourth material being a conductive material or a semiconductive material, the second barrier layer being made of an insulating material, the cover layer, the second barrier layer and the first connection layer forming a tunnel junction.

The capping layer comprises at least two superposed radiation-emitting layers made of a second semiconductor material, a first barrier layer made of a third semiconductor material having a third band-gap value strictly greater than the second band-gap value being interposed between each pair of successive radiation-emitting layers, and

the first radiation comprises a first set of electromagnetic waves, the radiation emitting layer is configured to emit a second radiation comprising a second set of electromagnetic waves, the emitter further comprises a radiation converter configured to absorb the second radiation and emit in response to the first radiation, a wavelength is defined for each electromagnetic wave, the first set of electromagnetic waves corresponds to a first wavelength range, and the second set of electromagnetic waves corresponds to a second wavelength range, the first wavelength range having a first average wavelength and the second wavelength range having a second average wavelength, the first average wavelength being different from the second average wavelength.

-at least one of the following properties is satisfied:

the ratio between the first thickness and the second thickness is between 1.5 and 6;

-the mesa has a minimum lateral dimension and a height, the height being measured in a first direction perpendicular to the substrate, the minimum lateral dimension being measured in a plane perpendicular to the first direction, the height being strictly smaller than the minimum lateral dimension;

the mesa forms a frustum with a base in contact with the substrate, said base being rectangular;

the mesa forms a frustum with a base in contact with the substrate, the base being hexagonal;

the mesa has a height measured along a first direction perpendicular to the substrate, said height being 100-

The upper surface has a surface of 9-900 square microns.

A transmitting device comprising at least two transmitters as defined previously is also proposed.

According to a particular embodiment, the transmitting means comprise one or more of the following features, taken alone or according to any possible combination:

the sides of the mesas are in contact with each other.

Each emitter comprises a first electrical contact electrically connected to a first portion of the emitter, the emitting device further comprises a single connecting structure comprising a mesa, a cover layer and a second electrical contact covering at least part of the upper surface and at least part of the side face of the mesa of the connecting structure, the second electrical contact being electrically connected to the substrate, each emitter being configured to emit a respective first radiation when an electrical current flows through the respective first electrical contact, the respective cover layer, the respective mesa, the substrate and the second electrical contact.

The transmitting means comprise three transmitters, each first radiation comprising a first set of electromagnetic waves, a wavelength being defined for each electromagnetic wave, each first set of electromagnetic waves corresponding to a first wavelength range, each first wavelength range having a respective first average wavelength, the first average wavelength of each transmitter being different from the first average wavelength of each other transmitter.

A display screen comprising a set of transmitting means as defined previously is also proposed.

The present description also relates to a method of manufacturing an emitter adapted to emit a first radiation, the method comprising the steps of:

-providing a substrate,

-creating a mesa of a first semiconductor material having a first bandgap value, the mesa having an upper surface and a side surface surrounding the upper surface and extending between the substrate (55) and the upper surface, and

-depositing a cover layer comprising one or more radiation emitting layers on the mesa, at least one radiation emitting layer being made of a second semiconductor material having a second band gap value being strictly smaller than the first band gap value, each radiation emitting layer having a first portion corresponding to the upper surface and a second portion corresponding to the lateral surface, a first thickness being defined for the first portion and a second thickness being defined for the second portion, the second thickness being strictly smaller than the first thickness.

The present specification further describes a method of manufacturing a transmitting device comprising a first transmitter and at least one second transmitter, each transmitter being adapted to transmit a respective first radiation, the method comprising the steps of:

-providing a substrate,

-creating for each emitter a mesa of a first semiconductor material having a first band gap value, the mesa having an upper surface and side surfaces surrounding the upper surface and extending between the substrate and the upper surface, and

-depositing on each mesa a covering layer comprising one or more radiation emitting layers, at least one radiation emitting layer being made of a second semiconductor material having a second band gap value strictly smaller than the first band gap value, each radiation emitting layer having a first portion corresponding to the upper surface and a second portion corresponding to the lateral surface, a first thickness being defined for the first portion and a second thickness being defined for the second portion, the second thickness being strictly smaller than the first thickness.

According to a particular embodiment, the substrate has a first side and a second side, the first side supporting the mesa, the first side and the second side being parallel to each other, each first radiation comprising a first set of electromagnetic waves, the radiation emitting layer of each second emitter being configured to emit a second radiation comprising a second set of electromagnetic waves, the method further comprising a step for forming, for each emitter, a first electrical contact electrically connected to the first portion, the emitter being configured to emit the respective first radiation when a current flows through the first electrical contact, the cover layer and the mesa. The method further comprises a step for connecting each first electrical contact to a control circuit adapted to generate each current, and a step for placing a radiation converter on the second side of the substrate, the radiation converter being configured to absorb a second radiation and to emit in response to a first radiation corresponding to a second emitter, a wavelength being defined for each electromagnetic wave, a first set of electromagnetic waves of the second emitter corresponding to a first wavelength range, a second set of electromagnetic waves corresponding to a second wavelength range, the first wavelength range having a first average wavelength, and the second wavelength range having a second average wavelength, the first average wavelength being different from the second average wavelength.

Drawings

The characteristics and advantages of the invention will become clear from the following description, given purely by way of non-limiting example, with reference to the accompanying drawings.

Figure 1 is a partial top view of a display screen comprising a set of emitting devices,

FIG. 2 is a side view of a section of the emitting devices along the line II-II of FIG. 1, each emitting device comprising a set of emitters,

fig. 3 is an enlarged side view of the emitter section of fig. 2.

Figures 4-12 are schematic illustrations of the results at various stages of an example of a method of manufacturing a transmitting device,

figures 13-17 are schematic side views of an example of a launching device,

FIGS. 18-20 are schematic illustrations of the results of the various stages of another example of a method of manufacturing a transmitting device, an

Fig. 21 is a schematic side view of another example of a transmitting device.

Detailed Description

The display screen 10 is shown in part in fig. 1 and is shown schematically in fig. 12.

The display screen 10 is, for example, integrated in an electronic device such as a mobile phone, a tablet computer or a laptop computer. In another embodiment, the display screen 10 may be integrated in a dedicated display device such as a television, a desktop computer screen, a smart watch, or smart glasses.

The display screen 10 is configured to display a set of images.

The display screen 10 comprises a set of emitting means 15 and a control circuit 20.

Each emitting device 15, also called "picture element", or simply "pixel", is configured for emitting at least one first radiation.

For convenience, the emitting device 15 is hereinafter referred to as a pixel 15.

For example, each pixel 15 is configured to emit one of a set of electromagnetic waves comprising three first radiations.

In a variant, embodiments with pixels 15 configured to emit more or less than three radiations (for example four) can be considered.

Each first radiation comprises a first set of electromagnetic waves.

A wavelength is defined for each electromagnetic wave.

Each first set of electromagnetic waves corresponds to a first wavelength range. The first wavelength range is a group formed by all wavelengths of the first group of electromagnetic waves.

A first average wavelength is defined for each first wavelength range.

Each pixel 15 comprises at least one light emitter 25 and at least one connection structure 30. For example, each pixel 15 comprises three light emitters 25 and a single connection structure 30.

Each light emitter 25 is configured to emit a respective first radiation. In particular, each light emitter 25 is configured to emit a respective first radiation when a first current flows through the light emitter 25.

The first average wavelength of each light emitter 25 is, for example, different from the first average wavelength of each other light emitter 25 of the same pixel 15.

According to one embodiment, the first average wavelength of one light emitter 25 is 430-480 nanometers (nm), the first average wavelength of another light emitter 25 is 500-560nm, and the first average wavelength of the third light emitter 25 is 580-680 nm.

Embodiments may also be considered in which the first average wavelengths of two different light emitters 25 of a single pixel 15 are the same.

As shown in FIG. 2, each light emitter 25 includes a substrate 55, a mesa 40, a cover layer 45, a first electrical contact 50, a radiation converter 52, and an insulating layer 60.

The substrate 55 is configured to support the mesa 40, the cover layer 45, and the first electrical contact 50.

Substrate 55 is, for example, common to all light emitters 25 and contact bumps or connection structures.

In some embodiments, the substrate 55 may further include a support plate 120. In the embodiment shown in fig. 2 and 3, the substrate 55 does not include any support plate 120.

The substrate 55 is, for example, planar. The planar substrate is a substrate having a planar major surface 65.

A normal direction D is defined for the substrate 55. The main surface 65 of the substrate 55 is perpendicular to the normal direction D.

The main surface 65 surrounds each mesa 40 in a plane perpendicular to the normal direction D.

The substrate 55 is made of a first semiconductor material. A first band gap value is defined for the first semiconductor material.

The expression "band gap value" is understood to mean the value of the forbidden band between the valence band and the conduction band of a material.

The band gap value is, for example, in electron volts (eV).

The valence band is defined as an energy band having the highest energy among energy bands allowed for electrons in the material while being completely filled at a temperature of less than or equal to 20 kelvin (K).

A first energy level is defined for each valence band. The first energy level is the highest energy level of the valence band.

The conduction band is defined as the band with the lowest energy among the energy bands allowed by electrons in the material, but is not completely filled at a temperature of 20K or less.

A second energy level is defined for each conduction band. The second energy level is the highest energy level of the conduction band.

Thus, each bandgap value is measured between a first energy level and a second energy level of the material.

A semiconductor material is a material with a band gap value strictly greater than zero and less than or equal to 6.5 eV.

The first semiconductor material is, for example, a group III nitride material. Group III nitride materials are a group of materials including GaN, AlN, and InN, and GaN, AlN, and InN alloys.

According to an embodiment, the first material is GaN.

Doping is defined as the presence of impurities in the material that can bring free charge carriers. Impurities are, for example, atoms of elements not naturally present in the material.

When an impurity increases the bulk density of holes in a material, the doped is p-type relative to the undoped material. The GaN layer is p-doped, for example, by adding magnesium (Mg) atoms.

When an impurity increases the bulk density of free electrons in a material, the doped is n-type relative to the undoped material. The GaN layer is n-doped, for example, by adding silicon (Si) atoms.

The first material is, for example, n-doped. However, in some embodiments, the type of doping may vary.

The first material is, for example, a crystalline material. A crystal or crystalline material is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microstructure, forming a lattice that extends in all directions.

A crystal structure is defined for the first material. In crystallography, the crystal structure is a description of the ordered arrangement of atoms, ions, or molecules in a crystalline material.

The crystal structure is, for example, a polar structure. Polar structures are crystal structures in which the centers of gravity of positive and negative charges are spatially separated.

The crystal structure, for example, has a polar orientation, at least one non-polar orientation, and at least one semi-polar orientation.

The polarity direction is a direction along which the centers of gravity of the positive and negative charges are spatially separated.

The non-polar direction is the direction along which the centers of gravity of the positive and negative charges are the same.

A semipolar direction is a direction that forms a non-zero angle with the polar axis of the material and each non-polar direction.

For example, the crystal structure is a hexagonal structure, such as wurtzite. Wurtzite is the most common crystal structure of group III nitrides. The polar axis of the wurtzite structure is called the c-axis.

The normal direction D is, for example, parallel to the polar direction of the crystal structure.

Insulating layer 60 extends over major surface 65. An insulating layer 60 surrounds each mesa 40, for example in a plane perpendicular to the normal direction D.

The insulating layer 60 is made of an electrically insulating material. The insulating layer 60 is made of silicon oxide, for example.

The insulating layer 60 forms a potential barrier between the cover layer 45 and the substrate 55. Specifically, the insulating layer 60 prevents current from flowing between the capping layer 45 and the substrate 55 without flowing through the mesa 40.

Each mesa 40 extends from the substrate 55 along the normal direction D.

Each mesa 40 has an upper surface 70, sides 75, and a base 80.

Mesa 40 is bounded by base 80 and upper surface 70 along normal direction D.

Each mesa 40 is, for example, in the shape of a frustum.

In geometry, a frustum is a solid portion lying between one or two parallel planes that cut the solid. A truncated pyramid is an example of a frustum.

For example, the mesa 40 is in the shape of a truncated, upright pyramid. In geometry, a pyramid is a polyhedron formed by joining a polygonal base 80 and a point called a vertex. The apex of the right pyramid is located directly above the centroid of its base 80.

More precisely, the mesa 40 has the shape of a truncated pyramid, the apex of which is aligned with the centroid of the base 80 in the normal direction D.

Each mesa 40 has a height h measured along the normal direction D and a lateral dimension measured in a plane perpendicular to the normal direction. Among the lateral dimensions, the smallest lateral dimension l of the mesa is defined as the dimension of the mesa 40, measured along the direction in which the mesa 40 has the smallest dimension among all directions perpendicular to the normal direction D.

When the mesa 40 is in the shape of a truncated right pyramid with an even number of sides of the base 80, the minimum transverse dimension/is the distance between two opposite sides of the base 80.

The height h is strictly smaller than the minimum transverse dimension l.

The height h is from 100nm to 2 μm, for example from 100nm to 1 μm.

Mesa 40 is made of a semiconductor material. For example, the mesa 40 is made of a first semiconductor material.

The mesa 40 is electrically connected to the substrate 55. In one embodiment, the mesas 40 are integrated with the substrate 55.

The upper surface 70 is, for example, planar. In the embodiment shown in fig. 2, the upper surface 70 is perpendicular to the normal direction D.

The upper surface 70 is polygonal.

As shown in fig. 1, the substrate 80 is, for example, rectangular. A square upper surface 70 is an example of a rectangular upper surface 70.

In other embodiments, the upper surface 70 is hexagonal or triangular.

The upper surface 70 has a surface area of 4-900 square microns (mum)²) Surface of (2), for example, 9 to 900 μm²。

Side 75 extends between substrate 55 and upper surface 70.

As shown in fig. 3, side 75 surrounds upper surface 70. The side faces 75 define the mesa 40 in a plane perpendicular to the normal direction D.

An axis a is defined for each point of the side 75. Axis a corresponds to the direction through the point and perpendicular to side 75 at that point.

At any point of the side 75, the angle α between the normal direction and the axis a is strictly less than 90 degrees (°). Specifically, the angle α is 30 ° to 80 °. For example, each axis a is perpendicular to the semipolar direction.

In other words, the angle β between the normal direction D and a line on the side 75, said line being included in a vertical plane including the normal direction D, is strictly greater than zero, for example 10 ° -60 °.

According to an embodiment, each angle α is 50-80 °. In other words, the angle β is 10 ° -40 °.

According to an embodiment, the angle α is 55-65 °.

The side 75 includes, for example, a plurality of flat surfaces. Specifically, when the table 40 is a truncated pyramid, each plane is rectangular and extends from one side of the base 80 to one side of the upper surface 70. In this case, the angle α of any two points of the same planar surface is the same.

According to an embodiment, the side faces 75 of at least two emitters 25 of a single pixel are in contact with each other.

The base 80 of the mesa 40 is in contact with the substrate 55.

The substrate 80 has a surface strictly higher than the surface of the upper surface 70.

The substrate 80 is polygonal. A rectangular or hexagonal substrate 80 is an example of a polygonal substrate 80. For example, the shape of the substrate 80 is the same as the shape of the upper surface 70.

According to the example shown in fig. 1, the sides of the base 80 of each mesa 40 are parallel to each other.

The cover layer 45 is shown in more detail in fig. 3.

A cover layer 45 covers at least a portion of the mesa 40.

The cover layer 45 is adapted to transmit a first current from the mesa 40 to the first electrical contact 50.

The cover layer 45 extends over at least a portion of the upper surface 70 and at least a portion of the side surfaces 75. Specifically, cover layer 45 has a top portion 77 in contact with upper surface 70 and side portions 78 in contact with side surfaces 75.

Each of the cover layers 45 is interposed between the first electrical contact 50 and the mesa 40 such that a first current flowing between the mesa 40 and the first electrical contact 50 flows through the cover layers 45.

The cover layer 45 includes at least one radiation emitting layer 85. For example, the capping layer 45 includes a plurality of stacked radiation emitting layers 85 and at least one first barrier layer 90.

The cladding layer 45 is configured such that when a first current flows through the cladding layer 45, the first current flows through each radiation emitting layer 85.

Each radiation emitting layer 85 is configured to emit radiation when a first current flows through the radiation emitting layer 85. For example, each radiation emitting layer 85 is configured to emit second radiation.

Each second radiation comprises a second set of electromagnetic waves.

Each second set of electromagnetic waves corresponds to a second wavelength range. The second wavelength range is a set formed by all wavelengths of the second set of electromagnetic waves.

A second average wavelength is defined for each second wavelength range. The second average wavelength is different from the first average wavelength of the first radiation corresponding to the light emitters 25 of which the radiation emitting layer 85 forms a part. For example, the second average wavelength is strictly less than the first average wavelength.

According to another embodiment, the second average wavelength is equal to the first average wavelength of the first radiation.

The first semiconductor material is transparent to the second radiation.

Each radiation emitting layer 85 is made of a second semiconductor material.

The second semiconductor material has a second band gap value. The second band gap value is strictly smaller than the first band gap value.

The second semiconductor material is a crystalline material. For example, the second semiconductor material has the same crystal structure as the first semiconductor material. Embodiments are contemplated in which the second semiconductor material has a different crystalline structure than the first semiconductor material.

The second semiconductor material is, for example, a group III-N material. Specifically, when the first semiconductor material is GaN, the second semiconductor material is InGaN.

Each radiation emitting layer 85 extends over a side surface 75 and the upper surface 70.

Specifically, each radiation emitting layer 85 covers at least a portion of side surfaces 75 and is on upper surface 70. In other words, each radiation emitting layer 85 is supported by side surfaces 75 and upper surface 70.

Each radiation emitting layer 85 has a first portion 95 and a second portion 100.

The first portion 95 of the radiation emitting layer 85 is a portion of the radiation emitting layer 85 that is a portion of the top portion 77 of the cover layer 45.

The first portion 95 corresponds to the upper surface 70. Specifically, first portion 95 covers at least a portion of upper surface 70. For example, first portion 95 completely covers upper surface 70.

The first portion 95 is perpendicular to the normal direction D.

The first portion 95 has a first thickness e 1. The first thickness e1 is measured along the normal direction D.

In the case of a single quantum well, the first thickness e1 is 1-20 nm.

The first portions 95 of all radiation emitting layers 85 in the same radiator 25 are superposed in the normal direction D. In other words, the first portion 95 forms a stack of first portions 95 stacked along the normal direction D.

The second portion 100 of the radiation emitting layer 85 is a portion of the radiation emitting layer 85 that is part of the side portion 78 of the cover layer 45.

The second portion 100 corresponds to the side 75. Specifically, second portion 100 covers at least a portion of side 75.

According to an embodiment, the second portion covers at least 30% of the surface of the side face 75. For example, second portion 100 covers at least 50% of side 75. Embodiments are contemplated in which the second portion 100 covers at least 90% of the side 75, and particularly covers the entire side 75.

For example, the above-described value of the percentage of the surface of the side face 75 covered by the second portion is calculated by considering only the surface of the side face 75 not in contact with the insulating layer 60.

However, an embodiment in which the percentage of the surface of side face 75 covered by the second portion is calculated by considering both the surface of side face 75 not in contact with insulating layer 60 and the surface of side face 75 covered by insulating layer 60 is contemplated.

Second portion 100 is perpendicular to axis a at any point on side 75.

The second portions 100 of all radiation emitting layers 85 are stacked on top of each other in the same emitter 25. In other words, these second portions 100 form a stack of second portions 100. The second portions 100 are stacked along an axis a.

Each second portion 100 has a second thickness e 2. The second thickness e2 is measured along the respective axis a at any point of the second portion 100.

The second thickness e2 is strictly smaller than the first thickness e 1. For example, the ratio of the first thickness e1 to the second thickness e2 is 1.5-6.

The second portion 100 is arranged such that the energy level of the charge carriers inside the second portion 100 is strictly higher than the energy level of the charge carriers inside the first portion 95.

Second thickness e2 is such that second portion 100 forms a quantum well for charge carriers in the second material.

Structurally, a single quantum well is fabricated by interposing a layer of a first semiconductor material between two layers of a second semiconductor material, the doped first and second semiconductor materials having different band gap values. In contrast, a multiple quantum well structure is a stack of semiconductor layers with alternating quantum wells and barriers.

Functionally, a quantum well is a structure in which quantum confinement occurs in one direction for at least one type of charge carrier. When the structural dimensions along this direction become equal to or smaller than the de broglie wavelength of the carriers, which are typically electrons and/or holes, quantum confinement effects occur, resulting in energy levels called "energy subbands".

In such quantum wells, the carriers may only have discrete energy values, but are generally able to move in a plane perpendicular to the direction in which the confinement occurs. As the size of the quantum well decreases along the direction in which the confinement occurs, the amount of energy available for carriers (also referred to as the "energy level") increases. Thus, since second thickness e2 of second portion 100 is less than first thickness e1 of first portion 95, the energy level in second portion 100 is higher than the energy level in first portion 95.

In quantum mechanics, "de broglie wavelength" is the wavelength of a particle when the particle is considered a wave. The de broglie wavelength of an electron is also referred to as the "electron wavelength". The de broglie wavelength of a charge carrier depends on the material in which the carrier is located.

A second portion 100 having a second thickness e2 strictly less than the product of the electron wavelength of the electrons in the second semiconductor material and five is an example of a quantum well.

The second thickness e2 is for example 0.3-10 nm.

Each barrier layer 90 is made of a third semiconductor material. The third semiconductor material has a third band gap value. The third bandgap value is strictly greater than the second bandgap value.

In an embodiment, the third semiconductor material is the first semiconductor material. For example, the third semiconductor material is a group III nitride material such as GaN.

The third semiconductor material is for example doped. The doping type of the third semiconductor material is, for example, different from the doping type of the first semiconductor material. In particular, the third semiconductor material is p-doped.

One barrier layer 90 is interposed between each pair of successive radiation-emitting layers 85.

In one embodiment, one barrier layer 90 also covers the radiation emitting layer 85 furthest from the mesa 40. The barrier layer 90 forms a potential barrier between the radiation emitting layer 85 furthest from the mesa 40 and the exterior of the emitter 25.

Each barrier layer 90 has a thickness of 1-30 nm. The first electrical contact 50 is configured to transmit a first current from the control circuit 20 to the cover layer 45.

The first electrical contact 50 is in contact with the top portion 77 of the cover layer 45. For example, the first electrical contact 50 is electrically connected to both the top portion 77 and the side portion 78, and thus to both the first portion 95 and the second portion 100 of the light emitting layer 85.

The first electrical contact 50 is made of, for example, a metal material.

In another embodiment, the first electrical contact 50 includes a connecting layer and a second barrier layer.

The connecting layer is made of a fourth material. The fourth material is a conductive material or a semiconductor material. The fourth material is doped with a dopant of the first conductivity type to be greater than 10¹⁹Atom/cm³Preferably greater than 10²⁰Atom/cm³Is heavily doped.

The second barrier layer is made of an electrically insulating material.

A second barrier layer is interposed between the connection layer and the capping layer 45.

The second barrier layer is configured such that the capping layer 45, the second barrier layer, and the connection layer form a tunnel junction.

In this case, the capping layer is a semiconductor heavily doped with a dopant of the second conductivity type, having a dopant concentration greater than 10¹⁹Atom/cm³Preferably greater than 10²⁰Atom/cm³. The second conductivity type is different from the first semiconductor type.

A tunnel junction is a structure that includes a potential barrier (e.g., a thin insulating layer or an electrical potential) between two conductive materials. Due to the thinness of the barrier, electrons can pass through the barrier by quantum tunneling techniques even if the barrier is made of an insulating material.

The second barrier layer has a thickness of 50-300 nm.

The radiation converter 52 is adapted to convert the second radiation into the first radiation.

The radiation converter 52 is a photoluminescent material, for example, a phosphor or a nanophosphor.

As a variant, the photoluminescent material is a set of particles. One example of a photoluminescent material is Yttrium Aluminum Garnet (YAG), also known as YAG: ce or YAG: ce3 +. The average size of the particles of conventional photoluminescent material is greater than 5 μm.

In an embodiment, the photoluminescent material is a matrix of nano-scale single crystal particles (hereinafter also referred to as semiconductor nanocrystals, or nano-phosphor particles hereinafter) having a semiconductor material dispersed therein.

According to one embodiment, the average size of the nanocrystals is in the range of 0.5 to 1,000nm, preferably 0.5 to 500nm, more preferably 1 to 100nm, especially 2 to 30 nm. For dimensions smaller than 50nm, the light conversion characteristics of semiconductor nanocrystals depend mainly on quantum confinement phenomena. The semiconductor nanocrystals then correspond to quantum boxes or quantum dots.

According to one embodiment, the semiconductor material of the semiconductor crystal is selected from: cadmium selenide (CdSe), indium phosphide (InP), cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium oxide (CdO), zinc cadmium oxide (ZnCdO), cadmium zinc sulfide (CdZnS), cadmium zinc selenide (CdZnSe), silver indium sulfide (AgInS2), and mixtures of at least two of these compounds.

The substrate is made of an at least partially transparent material. The substrate is made of, for example, silica. The matrix is for example made of any at least partially transparent polymer, in particular silicone, epoxy resin or polyacetic acid (PLA). The substrate may be made of an at least partially transparent polymer (e.g., PLA) that is used with a three-dimensional printer. According to one embodiment, the matrix comprises 2% to 90%, preferably 10% to 60%, for example about 20% by mass of nanocrystals.

According to other possible embodiments, the radiation converter 52 comprises a set of semiconductor particles embedded in a photosensitive resin. As shown in fig. 2, the radiation converter 52 is supported by a bottom surface 102 of the substrate 55 opposite the major surface 65 and facing the mesa 40.

The bottom surface 102 is, for example, parallel to the main surface 65. In the example shown in fig. 2, the bottom surface 102 defines the substrate 55 along the normal direction D.

The substrate 55 is bounded by the main surface 65 and the bottom surface 102, for example, along the normal direction D.

The distance between the bottom surface 102 and the main surface 65, measured in the normal direction, is, for example, 500nm to 50 μm.

The connection structure 30 is configured to electrically connect the substrate 55 and the control circuit 20.

The connection structure 30 includes, for example, a mesa 40, a capping layer 45, and a second electrical contact 105.

The mesa 40 and the cover layer 45 of the connection structure 30 are identical to the mesa 40 and the cover layer 45 of the light emitter.

The second electrical contact 105 electrically connects the control circuit 20 and the substrate 55. For example, the second electrical contact 105 connects the control circuit 20 and the substrate 55 through the insulating layer 60.

The second electrical contact 105 is made of a conductive material such as a metallic material.

The second electrical contact 105 is supported by the mesa 40 and the cover layer 45 of the connection structure 30. For example, the second electrical contact 105 covers at least a portion of the top portion 77 and the side portion 78 of the connection structure 30.

Control circuit 20 is configured to generate a first current corresponding to each light emitter 25 and to transmit each first current to the corresponding light emitter 25.

The control circuit 20 comprises, for example, connection pads 110 connected to the first or second electrical contacts 50, 105, respectively.

More precisely, the connection pad 110 corresponding to the second electrical contact 105 is in contact with a portion of the second electrical contact 105. Said portion of the second electrical contact 105 is interposed between the first portion 95 of the corresponding covering layer 45 and the connection pad 110.

The operation of the light emitter 25 will now be described.

When the control circuit 20 generates the first current, the first current flows through the second electrical contact 105, the substrate 55, the mesa 40, the cap layer 45, and the first electrical contact 50 in that order.

The current causes electrons and holes to reach each light emitting layer 85. Recombination of the electron-hole pairs in the one or more light emissive layers 85 results in emission of the second radiation.

At least a portion of the second radiation is absorbed by the converter 52. The absorption of the second radiation causes the converter to emit the first radiation.

During operation of the light emitter 25, charge carriers are repelled by the second portion 100 of the one or more light emissive layers 85 because the energy levels of the charge carriers in the second portion 100 are higher than the energy levels of the same carriers in the first portion 95. Thus, carriers are driven off the side surfaces 75 of the mesa 40.

Thus, surface recombination of carriers on the side 75 of mesa 40 is reduced when compared to light emitter 25 that does not include second portion 100. As a result, the emission efficiency of the light emitter 25 is higher than the emission efficiency of the light emitter 25 known in the prior art.

This effect increases as the lateral dimension of the mesa 40 decreases. Furthermore, the effect is stronger if 30% or more of the surface of the side face 75 is covered by the second portion 100.

Using a second portion 100 that is thinner than the first portion 95 is one way to obtain a higher energy level in the second portion 100 than in the first portion 95, which can be easily reproduced when the second portion 100 is thin enough to form a quantum well. The ratio of the first thickness to the second thickness of 1.5-6 corresponds to the energy difference between the first portion 95 and the second portion 100, which allows good repulsion of carriers from the second portion 100.

The deposition of the light-emissive layer 85 on the mesa 40 (angle a of the mesa 40 being 10-50) allows such a thin second portion 100 to be easily obtained. In fact, due to the geometry of typical material deposition chambers, material deposited on such sides 75 grows slower than when deposited on the upper surface 70.

Such easy obtaining of the pixel 15 will now be described with reference to an example of implementation of a method of manufacturing such a pixel 15, schematically illustrated in fig. 4-12.

The method of manufacturing the pixel 15 includes: the method comprises the steps of providing, creating, insulating, depositing, forming, connecting and placing.

During the providing step, a substrate 55 is provided. During the providing step, the substrate 55 comprises a support plate 120 supporting the substrate 55. The support plate 120 is, for example, a silicon or sapphire plate (see especially fig. 4).

During the creation step, each mesa 40 is created. For example, each mesa 40 is formed by etching away a portion of a block made of the first material.

According to an embodiment, each mesa 40 is formed by etching away a portion of the substrate 55 (see in particular fig. 5), in which case the bulk is the substrate 55.

According to a possible variant, the method comprises a step for depositing a layer of the first material onto the substrate 55. Thus, the layer is supported by the substrate 55. Each mesa 40 is then created by etching away a portion of the layer. Thus, in this case, the mass is a layer of the first material supported by the base plate 55.

In the insulating step, an insulating layer 60 is deposited on selected areas of the major surface of the substrate 55.

For example, an electrically insulating material is deposited on substrate 55 and mesa 40 and then removed from mesa 40. In other embodiments, a layer of photosensitive resin is deposited on mesa 40 such that only electrically insulating material is deposited on major surface 65.

The deposition step includes depositing each capping layer 45 on a respective mesa 40 (see in particular fig. 6). For example, the same capping layer 45 is deposited on each mesa 40.

For example, the deposition is performed using a deposition technique such as Metal Organic Chemical Vapor Deposition (MOCVD).

MOCVD is also called "MOVPE", which stands for "Metal-Organic Vapor phase epitaxy". Other Chemical Vapor Deposition (CVD) methods are also contemplated.

However, other deposition techniques may be used, such as Molecular Beam Epitaxy (MBE), gas source MBE (gsmbe), metal organic MBE (mombe), plasma assisted MBE (pambe), Atomic Layer Epitaxy (ALE), or Hydride Vapor Phase Epitaxy (HVPE).

The deposition of the light-emissive layer 85 results in the second thickness e2 being less than the first thickness e1 due to the different crystal orientations of the upper surface 70 and the side surfaces 75. The ratio between the first thickness e1 and the second thickness e2 depends inter alia on the angle α.

During the forming step, each first electrical contact 50 is formed. For example, each first electrical contact 50 and each second electrical contact 105 are deposited simultaneously on the respective mesa 40 and the cover layer 45, as shown in fig. 7.

In an embodiment, prior to deposition, a layer of protective resin is formed over the substrate 55, mesas 40 and cover layer 45 and patterned to leave only the areas where the electrical contacts 50, 105 are to be deposited (see fig. 8 and 9).

The electrical contacts 50, 105 are deposited, for example, using metal deposition techniques such as electron beam deposition, thermal evaporation, and sputter deposition.

Then, during the connecting step, each of the first and second electrical contacts 50, 105 is electrically connected to the control circuit 20 (see fig. 9).

The support plate is removed from the substrate 55 to expose the bottom surface 102 of the substrate 55 (see fig. 10).

Each radiation converter 52 is then formed onto the bottom surface 102 opposite the corresponding mesa 40. Photolithography is an example of a suitable method for placing such a transducer (see fig. 11).

The manufacture of the pixel has been previously described in the context of a pixel 15 comprising a plurality of light emitters. However, the method of manufacturing a single light emitter 25 may comprise steps for providing and steps for depositing, as long as only one mesa 40 is created during the creating step and only the cover layer 45 is deposited on the created mesa 40 during the depositing step.

Therefore, each manufacturing method is easily implemented.

Furthermore, since the mesas 40 are formed by etching away a portion of the existing mass of the first material, the shape of the mesas 40 can be effectively controlled. Specifically, the angle α may be arbitrarily selected and is not limited by the angle naturally obtained during growth. Therefore, an angle α that allows the ratio of the first thickness e1 and the second thickness e2 to be well repelled from the second portion 100 can be obtained. In particular, the angle α may be varied according to the desired thicknesses e1 and e 2.

The transmitter 25 also provides other advantages as now described.

When the first electrical contact 50 is electrically connected to the second portion 100, current propagates between the second portion 100 and the first electrical contact 50 along the axis a. When the axis a is parallel to the semipolar direction of the crystal structure, the injection of holes into the covering layer 45 is made easier.

Since the contact area between the cover layer 45 and the first electrical contact 50 is large, the voltage is reduced, and the electrical-to-optical conversion efficiency is improved (see fig. 14).

The presence of insulating layer 60 reduces electrical losses due to short circuits between substrate 55 and cover layer 45. The same effect can be obtained if the mesas 40 of adjacent light emitters are in contact with each other, since in this case also the electrical contact between the cover layer 45 and the substrate 55 is eliminated.

When the crystal structure of the material is hexagonal, the hexagonal shape of the base 80 causes the faces of the sides 75 to have the same characteristics as each other due to the hexagonal symmetry of wurtzite.

Furthermore, the hexagonal or rectangular base 80 allows the mesas 40 to be arranged on the substrate 55 in a compact manner and thus makes the pixels 15 smaller. Thus, the resolution of the display screen 10 comprising a set of pixels 15 is higher.

The use of the light converter 52 enables light emitters 25 having the same light-emitting layer 85 to emit different first radiations, in particular different colors of the first radiations, while being easy to manufacture, since only one deposition step is performed to deposit all the light-emitting layers 85.

When each of the three light emitters 25 of a single pixel 15 emits a different first radiation, said pixel may be used as a color pixel in a display screen.

However, embodiments are contemplated in which one or more of light emitters 25 do not include radiation converter 52. In this case, the radiation emitted by the light emitting layer 85 is the first emission.

For example, two light emitters 25 comprise radiation converters 52, but third light emitter 25 does not comprise any radiation converter 52, in particular when third light emitter 25 emits the first radiation of the blue color. In another embodiment, none of the light emitters 25 includes a radiation converter 52, e.g., if the second material of the light emitters 25 is different, the light emitting layer 85 of the light emitters 25 is configured to emit the first radiation having a different average wavelength.

The light emitter 25 lacking the radiation converter 52 is more efficient.

Further, embodiments are contemplated in which each light emitter 25 includes a radiation converter 52. For example, each radiation emitting layer 85 is ultraviolet radiation, and each radiation converter 52 converts the ultraviolet radiation to a respective first radiation.

The table 40 has been described above in the case of a truncated pyramid shape. However, the shape of the mesas 40 may vary.

In an embodiment, the mesa 40 is in the shape of a truncated cone. For example, the upper surface 70 and the base 80 are circular.

In the above example, only the second portion 100 has been described as a quantum well. However, embodiments are contemplated in which first portion 95 forms a quantum well. The emission efficiency of quantum wells is generally better than that of thicker layers.

Note that a planarization layer may be used. The planarization layer is a layer of material deposited on the substrate 55, on the mesas 40 and on the capping layer 45 such that the mesas 40 and the capping layer 45 are embedded in the planarization layer, thereby forming a planar surface. A planar surface may be beneficial for device processing and may provide a more uniform electrical implant (see fig. 17).

The planarization layer is made of, for example, a first semiconductor material.

In an embodiment, the planarization layer is doped. In particular, the planarization layer has a different doping type than the mesa 40.

In a specific example, the planarization layer is made of p-doped GaN.

The light emissive layer 85 has been described as a dense layer of a single material. Embodiments are also contemplated in which the light emitting layer 85 is a superlattice. A superlattice is a layer formed by a stack of sub-layers of two or more different materials, forming a pattern that repeats along the stacking direction, the sub-layers being so thin that quantum coupling exists between the sub-layers.

The different semiconductor materials described above are wurtzite structured group III nitride materials. However, other crystal structures and materials may be used.

Any of the first, second, third and fourth semiconductor materials may be selected, for example, from among arsenide materials such as AlAs, GaAs, InAs, phosphide materials such as AlP, GaP, InP, II-VI materials such as ZnSe, CdSe, ZnTe, CdTe, IV materials such as Si and Ge, or any alloy of these materials.

As a general description of different embodiments that may be considered, reference is made in particular to fig. 13-17, which are schematic side views of examples of pixels.

FIG. 13 corresponds to a mesa micro LED; FIG. 14 corresponds to overlapping p-type metals; FIG. 15 corresponds to a tunnel junction contact; fig. 16 corresponds to a compact mesa micro led, and fig. 17 corresponds to a compact mesa micro led with a flat surface.

Furthermore, embodiments may be considered in which a superlattice is added below the quantum wells.

Fig. 18-20 illustrate another example of a method for fabricating the pixel 15.

According to this example, capping layer 45 is deposited prior to depositing insulating layer 60. Thus, the capping layer 45 covers the mesa 40 and the major surface 65 (see fig. 18).

In a subsequent removal step, the portion of the cover layer 45 covering the main surface 65 is removed, for example by etching (see fig. 19). In an embodiment, the portion of the capping layer 45 that covers the lowermost portion of the mesa 40 and thus is in electrical contact with the major surface 65 is also removed.

An insulating step may optionally be performed after removal to cover major surface 65 with electrically insulating material (see fig. 20).

The connection structure 30 has been described above as including the mesa 40, the cover layer 45, and the second electrical contact 105. However, simpler embodiments are contemplated in which the connection structure includes only the second electrical contacts 105. In this case, the second electrical contact is, for example, a piece of conductive material having an overall height equal to that of the emitter 25 (see fig. 21).