阅读说明：本技术 红外led元件 (Infrared LED element ) 是由 杉山徹 喜根井聪文 饭塚和幸 中村薰 佐佐木真二 于 2020-03-26 设计创作，主要内容包括：实现发光波长超过1000nm、将光的取出效率比以往提高的红外LED元件。一种红外LED元件,具有：基板,包含InP,n型掺杂剂浓度为1×10～(17)/cm～(3)以上、小于3×10～(18)/cm～(3)；第一半导体层,形成在基板的上层,呈现n型；活性层,形成在第一半导体层的上层；第二半导体层,形成在活性层的上层,呈现p型；第一电极,形成在基板的面中的与形成有第一半导体层的一侧相反侧的第一面上；以及第二电极,形成在第二半导体层的上层,当从与基板的面正交的第一方向观察时,仅形成在第二半导体层的面的一部分区域中；主要的发光波长呈现1000nm以上。(An infrared LED element having an emission wavelength of more than 1000nm and improved light extraction efficiency compared with conventional ones is realized. An infrared LED element having: a substrate comprising InP and having an n-type dopant concentration of 1 × 10 17 /cm 3 Above and below 3 × 10 18 /cm 3 (ii) a A first semiconductor layer formed on the upper layer of the substrate and exhibiting an n-type; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer and exhibiting a p-type; a first electrode formed on a first surface of the substrate opposite to a side on which the first semiconductor layer is formed; and a second electrode formed on an upper layer of the second semiconductor layer, and formed only in a partial region of a surface of the second semiconductor layer when viewed from a first direction orthogonal to the surface of the substrate; the main emission wavelength is 1000nm or more.)

1. An infrared LED element, characterized in that,

comprising:

a substrate comprising InP and having an n-type dopant concentration of 1 × 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³；

A first semiconductor layer formed on the upper layer of the substrate and exhibiting an n-type;

an active layer formed on the first semiconductor layer;

a second semiconductor layer formed on the active layer and having a p-type structure;

a first electrode formed on a first surface of the substrate opposite to a side on which the first semiconductor layer is formed; and

a second electrode formed on an upper layer of the second semiconductor layer, the second electrode being formed only in a partial region of a surface of the second semiconductor layer when viewed from a first direction orthogonal to the surface of the substrate;

the main emission wavelength is 1000nm or more.

2. The infrared LED element as set forth in claim 1,

in the first direction, the thickness of the substrate is 10 times or more of the thickness of the second semiconductor layer.

3. The infrared LED element as set forth in claim 1 or 2,

the thickness of the substrate is 150 to 400 μm.

4. The infrared LED element as set forth in any one of claims 1 to 3,

the second electrode is formed only in a partial region of the surface of the second semiconductor layer;

in the first direction, at least a part of a region where the second electrode is not formed is opposed to at least a part of a region where the first electrode is formed.

5. The infrared LED element as set forth in any one of claims 1 to 4,

the second electrode has a plurality of partial electrodes in a grid shape or a comb shape extending in different directions on the surface of the second semiconductor layer;

the distance between the adjacent partial electrodes is 100 μm or less.

6. The infrared LED element as set forth in any one of claims 1 to 5,

the dopant of the substrate includes Sn.

Technical Field

The present invention relates to an infrared LED element, and particularly to an infrared LED element having an emission wavelength of 1000nm or more.

Background

Conventionally, development of a laser device for communication and measurement has been widely advanced as a light emitting device having an infrared region of 1000nm or more as an emission wavelength. On the other hand, there has been no application of such an LED element in the wavelength range, and development thereof has not progressed much compared with a laser element.

For example, patent document 1 below discloses that a GaAs-based light-emitting device can generate light having a wavelength of 0.7 to 0.8 μm (700 to 800nm), but an InP-based light-emitting device is required to generate light having a longer wavelength of about 1.3 μm (1300 nm). In particular, patent document 1 discloses: a p-type InP substrate is used as a growth substrate, and a p-type cladding layer lattice-matched to an InP crystal, an active layer, and an n-type cladding layer are epitaxially grown in this order to form an electrode.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 4-282875

Patent document 2: japanese examined patent publication (Kokoku) No. 6-103759

Patent document 3: japanese patent No. 3084364

Disclosure of Invention

Problems to be solved by the invention

As described above, there are cases where LED elements having an emission wavelength of more than 1000nm are not industrially useful so far, and development is not advanced so much. In contrast, in recent years, the demand for LED elements in such wavelength bands has also increased from the market, and LED elements with higher light intensity have been demanded.

In view of the above problems, it is an object of the present invention to improve light extraction efficiency of an infrared LED element having an emission wavelength of more than 1000nm, compared with the conventional one.

Means for solving the problems

As described above, laser devices have been developed mainly as light-emitting devices having an emission wavelength of more than 1000 nm. In order to improve the light emission efficiency, a method for injecting a large current has been studied so far in order to improve the light emission intensity in the active layer. For example, in the field of semiconductor lasers using InP substrates, a treatment is also performed to increase the current density that can be injected into the active layer by increasing the dopant concentration of InP to lower the resistivity of the substrate.

In view of the development of semiconductor lasers, it is conceivable that, in an InP-based LED element, a dopant is injected at a high concentration into an InP substrate in order to supply a large current to an active layer through the InP substrate. However, according to the special study of the inventors (or the inventors) of the present invention, it was confirmed that if the dopant concentration of the InP substrate is increased, the amount of light extracted decreases. The reason for this is presumed to be that: by increasing the dopant concentration of the InP substrate, diffusion of current flowing in the substrate in a direction parallel to the substrate surface (hereinafter, referred to as "lateral direction") is suppressed, and as a result, the current concentrates in a limited region in the active layer, and the region contributing to light emission in the active layer decreases.

In view of the above-described new findings of the present inventors (i), the present invention is an infrared LED element including: a substrate comprising InP and having an n-type dopant concentration of 1 × 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³(ii) a A first semiconductor layer formed on the upper layer of the substrate and exhibiting an n-type; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer and having a p-type structure; a first electrode formed on a first surface of the substrate opposite to a side on which the first semiconductor layer is formed; and a second electrode formed on the first electrodeAn upper layer of the second semiconductor layer formed only in a partial region of a surface of the second semiconductor layer when viewed from a first direction orthogonal to the surface of the substrate; the main emission wavelength is 1000nm or more.

When an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are epitaxially grown on an n-type InP substrate, the p-type semiconductor layer needs to be grown as thin as possible because the absorption coefficient of the p-type semiconductor layer is large. Therefore, if a p-side electrode is provided on the upper surface of the p-type semiconductor layer, an n-side electrode is provided on the surface (back surface) of the InP substrate opposite to the semiconductor layer, and a voltage is applied between these electrodes, a current tends to concentrate directly below the p-side electrode. In this case, light emission in the active layer located immediately below the p-side electrode becomes strong, the region in the active layer contributing to light emission becomes small, and the light emitted is easily absorbed by the p-side electrode, resulting in a decrease in light extraction efficiency.

Further, if the current is concentrated on a specific portion as described above, there is a problem that joule heat increases to increase defects in the active layer, and the light extraction efficiency is likely to further decrease by absorption of light by the defects.

In compound semiconductor light-emitting elements, several methods have been known to deal with current path concentration. For example, patent document 2 discloses a technique of forming a semiconductor layer transparent to generated light in a thick film at a position on an upper layer of an active layer. Further, patent document 3 discloses a method of forming a transparent electrode between an active layer and an upper electrode.

However, in an infrared LED element having an emission wavelength of more than 1000nm, that is, an InP-based (GaInAsP-based) infrared LED element, there is a problem that crystal quality is decreased and defect density is increased by making the film thickness thick. In addition, the p-type semiconductor layer may have a large absorption coefficient as described above. In view of this, even if the method described in patent document 2 is applied to an infrared LED element having an emission wavelength exceeding 1000nm as it is, the effect of improving the light extraction efficiency is not obtained. In, which is a component constituting a semiconductor layer of a GaInAsP-based infrared LED element, is a rare metal whose production area is important. Therefore, making the semiconductor layer thick causes other problems such as stable securing of raw materials and increase in manufacturing cost.

As described in patent document 3, a technique of dispersing a current in a horizontal direction using a transparent electrode such as ITO is widely used for a semiconductor light emitting element in which an emission wavelength is in a visible light region. However, ITO generally used as a transparent electrode absorbs infrared light having an emission wavelength of more than 1000 nm. Therefore, even if the method described in patent document 3 is applied to an infrared LED element having an emission wavelength exceeding 1000nm as it is, the effect of improving the light extraction efficiency cannot be obtained.

As a result of the present inventors'(s) specialized studies, the following new findings were found: in an infrared LED element in which the main emission wavelength is 1000nm or more, if the n-type dopant concentration of an InP-containing substrate is lower than that of a conventional one doped for lowering the resistance, an effect of dispersing the current in the lateral direction (direction parallel to the surface of the substrate) can be obtained. That is, according to the infrared LED element of the present invention, the n-type dopant concentration of the substrate is set to 1 × 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³Since the resistivity of the substrate is slightly lower than that of the second semiconductor layer which is p-type, electrons easily move in the lateral direction in the substrate, and a current flowing in the active layer can be diffused in the lateral direction.

The resistivity within the semiconductor layer is determined by the carrier concentration, which is approximately dependent on the dopant concentration. Here, the second semiconductor layer exhibiting p-type is usually increased in dopant concentration to the vicinity of the upper limit of the amount of implantation, for example, 5 × 10 concentration, from the viewpoint of functioning as a cladding layer for the active layer¹⁷/cm³Above, 3 × 10¹⁸/cm³The following. On the other hand, the n-type dopant concentration of the substrate was 1 × 10 as described above¹⁷/cm³Above and below 3 × 10¹⁸/cm³The concentration of the p-type dopant in the second semiconductor layer is equal to or less than that in the first semiconductor layer. Thereby, the resistivity of the substrate, i.e. the n side, is made to be the second semiconductorThe resistivity of the bulk layer, i.e., the p-side, is relatively higher.

In the first direction, the thickness of the substrate may be 10 times or more of the thickness of the second semiconductor layer.

As described above, in the infrared LED element having an emission wavelength of more than 1000nm, if the film thickness of the semiconductor layer (second semiconductor layer) exhibiting p-type conductivity is increased, the absorption coefficient is increased, and the light extraction efficiency is lowered. On the other hand, since InP has a high cleavability, it is necessary to set the thickness of at least the substrate to 50 μm or more, preferably 150 μm or more, and more preferably 200 μm or more, from the viewpoint of securing self-supporting properties.

In this way, when the thickness of the substrate is 10 times or more the thickness of the second semiconductor layer, the substrate is thick, and therefore, the effect of diffusion in the lateral direction when a current flows in the substrate becomes remarkable by intentionally reducing the n-type dopant concentration of the substrate. As a result, the current flowing in the active layer is further diffused in the lateral direction, and the light extraction efficiency is improved.

In addition, the thickness of the substrate is preferably 700 μm or less, and more preferably 400 μm or less, from the viewpoint of incorporating the infrared LED element into a general package.

The second electrode may be formed only in a partial region of the surface of the second semiconductor layer; in the first direction, at least a part of a region where the second electrode is not formed is opposed to at least a part of a region where the first electrode is formed.

According to the above configuration, the first electrode formed on the first surface side of the substrate and the second electrode formed on the surface (referred to as "second surface") side opposite thereto are arranged at positions that do not completely face each other with respect to the first direction. As a result, the effect of spreading the current flowing between the first electrode and the second electrode in the lateral direction is further enhanced.

Further, by forming the second electrode in a part of the surface of the second semiconductor layer, not only the side surface of the substrate but also the surface of the second semiconductor layer can be a light extraction surface, and light extraction efficiency can be improved.

In the above configuration, the first electrode disposed on the first surface side of the substrate may be formed only on a part of the first surface of the substrate. In this case, it is preferable that the first electrode and the non-formation region of the second electrode are opposed to each other with respect to the first direction, and the second electrode and the non-formation region of the first electrode are opposed to each other with respect to the first direction.

The second electrode may have a plurality of partial electrodes in a grid shape or a comb shape extending in different directions on the surface of the second semiconductor layer; the distance between the adjacent partial electrodes is 100 μm or less.

By setting the concentration of the n-type dopant in the substrate to 1X 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³The current dispersion length can be 50 μm or more. Here, the "dispersion length" refers to a distance in the lateral direction of the second electrode from a portion where the luminance of 1/2 is exhibited with respect to the luminance in the vicinity of the second electrode.

By setting the distance between the partial electrodes to 100 μm or less, the currents flowing from the plurality of partial electrodes arranged apart from each other overlap, and as a result, the current can be caused to flow into the active layer over a wide range in the lateral direction.

The dopant of the substrate may contain Sn. At 1X 10 as described above¹⁷/cm³Above and below 3 × 10¹⁸/cm³When InP is doped with the dopant concentration of (3), the density of crystal defects can be reduced by including Sn in the dopant.

The substrate may have a reflective layer made of a material having a higher reflectance with respect to light generated by the active layer than the first electrode in a region of the first surface where the first electrode is not formed.

According to the above configuration, particularly in the infrared LED element having the side surface of the substrate or the surface on the second electrode side as the light extraction surface, since the light can be returned into the substrate even when the light travels in a direction different from the direction of the extraction surface, a decrease in the extraction efficiency is suppressed.

The reflective layer may include 1 or more materials included in a group consisting of Ag, Ag alloy, Au, and Al.

The infrared LED element may have a dielectric layer made of a material having a refractive index smaller than that of the substrate by 0.2 or more in a region of the first surface of the substrate where the first electrode is not formed.

With this structure, total reflection is likely to occur at the boundary between the substrate and the specific region. As a result, in particular, in the infrared LED element having the side surface of the substrate and the surface on the second electrode side as the light extraction surface, even when light travels in a direction different from the extraction surface, the light can be returned into the substrate, and therefore, a decrease in extraction efficiency is suppressed.

The dielectric layer may be made of SiO₂、SiN、Al₂O₃And ZnO and ITO, and 1 or more of the above materials.

The substrate may have a side surface other than the first surface and a second surface opposite to the first surface, the side surface including a concave-convex portion. Since InP has a refractive index of 3.0 or more and a large value, the refractive index difference between the substrate and the air becomes large, and light extraction becomes difficult. Therefore, by providing the uneven portion on the side surface of the substrate, total reflection on the side surface is less likely to occur, and light extraction efficiency is improved.

Further, if the uneven portion is formed on the surface of the second semiconductor layer, the second semiconductor layer may have a region with a reduced thickness, and therefore, the effect of diffusing a current in the lateral direction may be reduced. From this viewpoint, it is preferable that no concave-convex portion be formed on the surface of the second semiconductor layer.

In particular, when the substrate has a thickness 10 times or more the thickness of the semiconductor layer, the surface area of the side surface is increased, and therefore most of the light generated in the active layer is extracted from the side surface of the substrate. Therefore, in order to suppress total reflection on the side surface and improve the light extraction efficiency, it is preferable to provide a concave-convex portion on the side surface.

Effects of the invention

According to the infrared LED element of the present invention, the light extraction efficiency is improved in a region where the emission wavelength exceeds 1000nm as compared with the conventional one.

Drawings

Fig. 1 is a sectional view schematically showing the structure of a first embodiment of an infrared LED element according to the present invention.

Fig. 2 is an example of a schematic plan view of the infrared LED element shown in fig. 1 when viewed from the + Z direction.

Fig. 3A is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3B is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3C is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3D is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3E is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3F is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3G is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3H is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 3I is a cross-sectional view for explaining a step of the method for manufacturing the infrared LED element shown in fig. 1.

Fig. 4A is a graph showing the relationship between the dopant concentration and the emission intensity of the substrate in the infrared LED element manufactured through the steps SA1 to SA 11.

Fig. 4B is a graph showing the relationship between the dopant concentration and the dispersion length of the substrate in the infrared LED element manufactured through the steps SA1 to SA 11.

Fig. 5 is a plan view schematically showing another configuration of the first embodiment of the infrared LED element of the present invention.

Fig. 6 is a sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention.

Fig. 7 is a sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention.

Fig. 8 is a cross-sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention.

Fig. 9 is a sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention.

Fig. 10 is a sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention.

Detailed Description

An embodiment of an infrared LED element according to the present invention will be described with reference to the drawings. The following drawings are schematic, and the dimensional ratio in the drawings does not necessarily coincide with the actual dimensional ratio. In addition, the size ratio may not be uniform between drawings.

In the present specification, the description of "GaInAsP" refers to a mixed crystal of Ga, In, As and P, and the description of the composition ratio is omitted. The same applies to other descriptions such as "AlGaInAs".

In the present specification, the expression "a layer B is formed on a layer a" means not only a case where the layer B is directly formed on the surface of the layer a but also a case where the layer B is formed on the surface of the layer a via a thin film. The term "thin film" as used herein means a layer having a thickness of 10nm or less, and preferably 5nm or less.

[ first embodiment ]

The structure of the first embodiment of the infrared LED element of the present invention will be explained.

< construction >

Fig. 1 is a sectional view schematically showing the structure of an infrared LED element according to the present embodiment. The infrared LED element 1 shown in fig. 1 includes a substrate 3 and a semiconductor layer 10 formed on the substrate 3. The infrared LED element 1 is provided with electrodes (21, 22, 23) for injecting current.

Fig. 1 corresponds to a schematic cross-sectional view of the infrared LED element 1 cut at a predetermined position along the XZ plane. Hereinafter, the XYZ coordinate system attached to fig. 1 is appropriately referred to. According to the coordinate system shown in fig. 1, the Z direction corresponds to the "first direction".

Fig. 2 is an example of a schematic plan view of the infrared LED element 1 as viewed from the + Z direction. For convenience of explanation, the electrode 23 is not shown in fig. 2.

(substrate 3)

In the present embodiment, the substrate 3 is made of InP doped with an n-type impurity. In this case, the n-type corresponds to "the first conductivity type". As the n-type impurity material doped into the substrate 3, Sn, Si, S, Ge, Se, or the like can be used, and Sn is particularly preferable.

The thickness (length in the Z direction) of the substrate 3 is 50 μm or more and 700 μm or less. Since InP has a high cleavability, the thickness of the substrate 3 needs to be at least 50 μm or more in order to ensure self-supporting properties. In addition, from the viewpoint of incorporating the infrared LED element 1 into a normal package, the thickness of the substrate 3 needs to be 700 μm or less. The thickness of the substrate 3 is preferably 150 μm or more, and more preferably 200 μm or more. The thickness of the substrate 3 is preferably 400 μm or less.

The dopant concentration of the n-type impurity of the substrate 3 is 1X 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³More preferably 3X 10¹⁷/cm³Above, 3 × 10¹⁸/cm³Hereinafter, 5 × 10 is particularly preferable¹⁷/cm³Above, 3 × 10¹⁸/cm³The following. In addition, when Sn is used as the dopant, the quality of the InP crystal constituting the substrate 3 can be maintained in a particularly good state while implanting impurities at a dopant concentration in the above numerical range.

The dopant concentration is a slightly lower value than that in the case where the InP substrate is doped to increase the conductivity. Therefore, from the viewpoint of suppressing the resistance of the substrate 3 itself from becoming excessively high, it is also preferable to use the substrateThe thickness of 3 is set to 700 μm or less. For example, if the current density is set to 150A/cm²A potential difference of 0.1V or more is generated by the internal resistance of the substrate 3 having a thickness of 700 μm or more. As described later with reference to fig. 4B, considering that the driving voltage of the infrared LED element 1 is, for example, about 1.0V, a potential difference of 10% or more occurs in the substrate 3, which is not preferable. On the other hand, for example, in the case of the substrate 3 having a thickness of 400 μm, the potential difference due to the internal resistance is suppressed to 0.06V and less than 0.1V.

The substrate 3 is formed by doping an InP crystal with the n-type impurity, but other impurities may be mixed in a small amount (for example, less than 1%).

(semiconductor layer 10)

In the present embodiment, the semiconductor layer 10 is formed on the surface 3b of the substrate 3. The face 3b corresponds to a "second face".

In the example shown in fig. 1, the semiconductor layer 10 includes a first semiconductor layer 11, an active layer 12, and second semiconductor layers (13, 14), which are stacked.

The first semiconductor layer 11 is formed on the second face 3b of the substrate 3. The first semiconductor layer 11 is an InP layer doped with n-type impurities, and constitutes an n-type cladding layer of the infrared LED element 1. The n-type dopant concentration of the first semiconductor layer 11 is preferably 1 × 10¹⁷/cm³Above, 5 × 10¹⁸/cm³Hereinafter, more preferably 5 × 10¹⁷/cm³Above, 4 × 10¹⁸/cm³The following. As the n-type impurity material doped into the first semiconductor layer 11, Sn, Si, S, Ge, Se, or the like can be used, and Si is particularly preferable.

As will be described later, the active layer 12 generates infrared light having a main emission wavelength of 1000nm or more and less than 1800 nm. The first semiconductor layer 11 is appropriately selected from materials that do not absorb light in the wavelength band and that can be epitaxially grown in lattice-matching with the substrate 3 made of InP. For example, as the first semiconductor layer 11, in addition to InP, a material such as GaInAsP or AlGaInAs may be used.

The film thickness of the first semiconductor layer 11 is 0.1 μm or more and 10 μm or less, and preferably 0.5 μm or more and 5 μm or less.

The active layer 12 is formed on the upper layer (+ Z direction position) of the first semiconductor layer 11. The active layer 12 is made of a material that generates infrared light having a main emission wavelength of 1000nm or more and less than 1800 nm. The active layer 12 is appropriately selected from materials that can generate light of a target wavelength and can be epitaxially grown in lattice matching with the substrate 3 made of InP. For example, the active layer 12 may have a single-layer structure of GaInAsP, InGaAs, or AlGaInAs, or may have an MQW (Multiple Quantum Well) structure including Well layers made of GaInAsP, InGaAs, or AlGaInAs and barrier layers made of GaInAsP, InGaAs, AlGaInAs, or InP having a larger band gap energy than the Well layers.

The active layer 12 may be doped n-type or p-type, or may be undoped. In the case of being doped n-type, Si, for example, can be used as the dopant.

The thickness of the active layer 12 is 100nm to 2000nm, preferably 500nm to 1500nm, when the active layer 12 has a single-layer structure. When the active layer 12 has an MQW structure, a well layer and a barrier layer having a film thickness of 5nm to 20nm are stacked in a range of 2 cycles to 50 cycles.

The second semiconductor layers (13, 14) are formed on the upper layer (+ Z direction position) of the active layer 12. The second semiconductor layers (13, 14) are both doped with p-type impurities. The second semiconductor layer 13 constitutes a p-type cladding layer of the infrared LED element 1, and the second semiconductor layer 14 constitutes a p-type contact layer of the infrared LED element 1. The second semiconductor layer 14 is a layer doped at a high concentration in order to secure electrical connection with a second electrode 21 described later. However, when sufficient electrical connection can be secured, the second semiconductor layer 14 may be omitted and the second electrode 21 may be brought into direct contact with the second semiconductor layer 13 constituting the p-type cladding layer.

For example, the second semiconductor layer 13 constituting the p-type cladding layer is formed of InP doped with Zn, and the second semiconductor layer 14 constituting the p-type contact layer is formed of GaInAsP doped with Zn.

The concentration of the p-type dopant in the second semiconductor layer 13 constituting the p-type cladding layer is preferably 8 × 10¹⁷/cm³Above, 3 × 10¹⁸/cm³Hereinafter, more preferably 1 × 10¹⁸/cm³Above, 3 × 10¹⁸/cm³The following. In addition, the concentration of the p-type dopant in the second semiconductor layer 14 constituting the p-type contact layer is preferably 5 × 10¹⁷/cm³Above, 3 × 10¹⁸/cm³Hereinafter, more preferably 1 × 10¹⁸/cm³Above, 3 × 10¹⁸/cm³The following. Further, as the diffusion prevention layer of Zn doped in the second semiconductor layers (13, 14), a layer having a low concentration of a p-type dopant may be interposed between the active layer 12 and the second semiconductor layers (13, 14).

As the p-type impurity material doped into the second semiconductor layers (13, 14), Zn, Mg, Be, or the like can Be used, and Zn or Mg is preferable, and Zn is particularly preferable. The p-type dopant of second semiconductor layer 13 constituting the p-type cladding layer and the p-type dopant of second semiconductor layer 14 constituting the p-type contact layer may be the same or different materials.

(electrodes 21, 22, 23)

The infrared LED element 1 has electrodes (21, 22, 23).

A first electrode 22 is formed on the first surface 3a of the substrate 3. The first electrode 22 makes ohmic contact with the first face 3a of the substrate 3. The first electrode 22 may be made of a material such as AuGe/Ni/Au, Pt/Ti, Ge/Pt, or the like, and may include a plurality of these materials. In the present specification, the expression "X1/X2" used in the description of the material means that a layer made of X1 and a layer made of X2 are stacked.

On the surface of the second semiconductor layer 14, a second electrode 21 is formed. The second electrode 21 makes ohmic contact with the surface of the second semiconductor layer 14. The second electrode 21 may be made of a material such as Au/Zn/Au, AuZn, and AuBe, and may include a plurality of these materials.

On the surface of the second electrode 21, a pad electrode 23 is formed. The pad electrode 23 forms a region for connecting a bonding wire. The pad electrode 23 is made of, for example, Ti/Au, Ti/Pt/Au, or the like.

In the example shown in fig. 2, the second electrode 21 has an electrode region 21b in which the pad electrode 23 is disposed and an electrode region 21a extending linearly from the electrode region 21 b. The electrode region 21a is provided for the purpose of spreading the current in a direction parallel to the XY plane.

(concave-convex part 41)

In the present embodiment, the concave-convex portion 41 is formed on the side surface of the substrate 3. Here, the side surface of the substrate 3 refers to a surface other than two surfaces (3a and 3b) parallel to the XY plane among the surfaces of the substrate 3 as shown in fig. 1. In the case where the substrate 3 has a substantially rectangular parallelepiped shape, the substrate 3 has 4 side surfaces, and the concave and convex portions 41 are formed on both of these side surfaces.

The uneven portion 41 is configured such that the maximum value of the height difference is 0.5 times or more the emission wavelength and the interval between the projections and the recesses is 0.7 times or more the emission wavelength. For example, the maximum value of the height difference of the uneven portion is preferably 0.5 μm or more and 3 μm or less, and more preferably 0.8 μm or more and 2 μm or less. The interval between the projections and the recesses, that is, the pitch of the uneven portions 41 is preferably 0.8 μm or more and 4 μm or less, and more preferably 1.4 μm or more and 3 μm or less.

< manufacturing method >)

An example of the method for manufacturing the infrared LED element 1 will be described with reference to fig. 3A to 3I. Fig. 3A to 3I are cross-sectional views of a step in the manufacturing process.

(step S1)

As shown in FIG. 3A, the prepared substrate is 1 × 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³Substrate 3 formed of InP doped with n-type impurities.

(step S2)

As shown in fig. 3A, the substrate 3 is transported into an mocvd (metal Organic Chemical Vapor deposition) apparatus, and the semiconductor layer 10 including the first semiconductor layer 11, the active layer 12, and the second semiconductor layers (13, 14) is epitaxially grown in this order toward the second surface 3b side of the substrate 3. In step S2, the type and flow rate of the source gas, the processing time, the ambient temperature, and the like are appropriately adjusted according to the material and the film thickness of the layer to be grown.

Examples of the material of each semiconductor layer 10 are as described above. As an example, the epitaxial growth step forms the semiconductor layer 10 including the first semiconductor layer 11 formed of InP doped with Si, the active layer 12 formed of GaInAsP, the second semiconductor layer 13 formed of InP doped with Zn, and the second semiconductor layer 14 formed of GaInAsP doped with Zn. Through this step, an epitaxial wafer in which the semiconductor layer 10 is formed on the surface of the substrate 3 is obtained.

(step S3)

The epitaxial wafer is taken out of the MOCVD apparatus, and a resist mask patterned by photolithography is formed on the surface of the second semiconductor layer 14. Then, after a film of a material (e.g., Au/Zn/Au) for forming the second electrode 21 is formed by using a vacuum vapor deposition apparatus, the resist mask is peeled off by a lift-off method. Then, for example, an alloy treatment (annealing treatment) is performed by a heating treatment at 450 ℃ for 10 minutes, and as shown in fig. 3B, the second electrode 21 is formed on the upper surface of the second semiconductor layer 14.

(step S4)

A resist is applied to and protected by a surface of the substrate 3 on the side where the semiconductor layer 10 is formed, and then a first surface 3a, which is the surface opposite to the surface, is subjected to a grinding and polishing treatment and a wet etching treatment with a hydrochloric acid-based etchant. Thereby, the thickness of the substrate 3 is adjusted (see fig. 3C). The thickness of the substrate 3 is set to 50 μm or more and 700 μm or less as described above, and is set to 250 μm as an example. Then, the resist as a protective film is removed by an organic solvent.

(step S5)

As shown in fig. 3D, after a material (e.g., AuGe/Ni/Au) for forming the first electrode 22 is formed on the first surface 3a side of the substrate 3 by using a vacuum evaporation apparatus, an alloying treatment (annealing treatment) is performed by, for example, a heating treatment at 450 ℃ for 10 minutes to form the first electrode 22.

(step S6)

As shown in fig. 3E, a pad electrode 23 made of, for example, Ti/Au is formed on the upper surface of the second electrode 21 by photolithography, vacuum evaporation, or lift-off.

(step S7)

As shown in fig. 3F, mesa etching for element separation is applied. Specifically, a wet etching treatment is performed using a mixture of bromine and methanol while masking a non-etched region in the surface of the second semiconductor layer 14 with a resist patterned by photolithography. Thus, the second semiconductor layers (13, 14), the active layer 12, and a part of the first semiconductor layer 11 located in the region not masked are removed.

(step S8)

As shown in fig. 3G, after the wafer subjected to the mesa etching process is pasted to the dicing sheet 31, the element separation is performed along the dicing line using a blade dicing apparatus. Further, the cut piece 31 to which the infrared LED elements 1 are attached is spread by using a spreading device, and a gap is provided between the adjacent infrared LED elements 1.

(step S9)

As shown in fig. 3H, the cut piece 31 to which the infrared LED element 1 is attached is subjected to an immersion treatment with an acidic etching solution containing hydrochloric acid, thereby forming a concave-convex shape on the side surface of the infrared LED element 1. In step S9, concave-convex portion 41 is formed on the side surface of substrate 3, and concave-convex portion 42 is formed on the side surface of semiconductor layer 10.

Although not shown in fig. 3H, in step S9, a concave-convex portion may be formed on the upper surface of the second semiconductor layer 14.

(step S10)

The infrared LED element 1 is detached from the dicing sheet 31. This brings the state shown in fig. 1.

(step S11)

As shown in fig. 3I, for example, the first electrode 22 side of the infrared LED element 1 is die-bonded TO a TO-18 type stem 35 via a silver paste 34, and after thermal curing, the pad electrode 23 and a wire 36 are bonded and electrically connected. In step S11, brazing may be used instead of the silver paste 34. As the brazing, AuSn, SnAgSu, or the like can be used.

< action >

When a voltage is applied between the first electrode 22 and the second electrode 21 of the infrared LED element 1 manufactured through the steps S1 to S11, a current flows into the active layer 12, and light is emitted. Of this light, light traveling in the + Z direction is extracted from the surface of the second semiconductor layer 14 facing the outside. Further, the light traveling in the-Z direction is taken out from the side through the substrate 3.

Here, since the concave-convex portion 41 is formed on the side surface of the substrate 3, the amount of light that is totally reflected by the side surface of the substrate 3 and returned to the inside of the substrate 3 again is suppressed.

Further, the dopant concentration of the substrate 3 is 1 × 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³The concentration of the dopant is lower than the concentration of the dopant to be doped in the field of semiconductor laser for the purpose of lowering the resistivity of the substrate. By setting the dopant concentration to a value within such a range, the current flowing in the substrate 3 is diffused in the lateral direction (direction parallel to the XY plane), and as a result, the current flows in a wide range in the active layer 12, so that the light emitting region is enlarged, and the light extraction efficiency is improved.

Fig. 4A and 4B are graphs showing the relationship between the emission intensity and the dispersion length of each of the plurality of infrared LED elements 1 manufactured through the steps of steps S1 to S11 with the dopant concentration of the substrate 3 being different from each other, and the dopant concentration. Fig. 4A is a graph showing the relationship between the dopant concentration and the emission intensity. Fig. 4B is a graph showing the relationship between the dopant concentration and the dispersion length.

More specifically, fig. 4A is a graph showing the results of evaluating the emission intensity by the integrating sphere system when a current of 50mA is injected to the infrared LED element 1 manufactured by varying the dopant concentration of the substrate 3, in accordance with the dopant concentration.

Fig. 4B is a graph showing the results of measuring the "dispersion length" defined by the distance between the portion with the highest luminance and the portion with the luminance lowered to 1/2 in the state where the infrared LED elements 1 manufactured with different dopant concentrations of the substrate 3 emit light, respectively, in accordance with the dopant concentrations. The dispersion length is a value derived from a comparison result of numerical values corresponding to positions, which is obtained by imaging the surface of each infrared LED element 1 in a state where each infrared LED element 1 is actually caused to emit light, converting the brightness corresponding to the surface position into a numerical value based on the imaging result.

From FIG. 4A, it was confirmed that the dopant concentration in the substrate 3 was 1X 10¹⁷/cm³Above, 1 × 10¹⁹/cm³In the following range, the emission intensity increases as the dopant concentration of the substrate 3 is decreased. Further, it was confirmed from fig. 4B that the dispersion length increased as the dopant concentration of the substrate 3 was decreased. From the above results, as described in the section "means for solving the problem", the dopant concentration of the substrate 3 is set to 1 × 10¹⁷/cm³Above and below 3 × 10¹⁸/cm³In the range of (3), the current flowing in the substrate 3 is diffused in the lateral direction, and the current flowing in the active layer 12 is diffused in the lateral direction, and it is considered that the light emission efficiency is improved.

From the results shown in FIG. 4B, the dispersion length can be 50 μm or more. Therefore, in order to allow a current to flow in a wide range in the active layer 12, when the distance d1 (see fig. 2) is provided to the second electrode 21, it is preferable that the distance be set to 100 μm or less.

The shape of the second electrode 21 shown in fig. 2 is merely an example, and in the present embodiment, the shape of the second electrode 21 provided in the infrared LED element 1 is arbitrary. For example, as shown in fig. 5, the second electrode 21 may have an electrode region 21b in which the pad electrode 23 is disposed and an electrode region 21a which is connected to the electrode region 21b and extends in a linear shape, and the electrode region 21a may have a grid shape. In this case, the distance d1 between the electrode regions 21a constituting the grid is preferably set to, for example, 100 μm or less.

[ other embodiments ]

Other embodiments of the infrared LED element 1 will be described below.

<1> as shown in fig. 6, the first electrode 22 may be formed in a part of the first surface 3a of the substrate 3. In this case, at least a part of the first electrode 22 is preferably disposed so as to face a region where the second electrode 21 is not formed with respect to the Z direction. That is, it is preferable that the electrodes (21, 22) are disposed so that at least a part of the region B1 where the first electrode 22 is formed faces the region a2 where the second electrode 21 is not formed in the Z direction. Thereby, the current is spread in the lateral direction (direction parallel to the XY plane), the current flows in a wide range within the active layer 12, and the emission intensity is improved.

Further, by making the region B2 where the first electrode 22 is not formed a void, the difference in refractive index becomes large at the boundary surface between the substrate 3 and the region B2. As a result, the light traveling in the-Z direction in the substrate 3 is easily totally reflected on the surface (first surface 3a) on the-Z side of the substrate 3, and the amount of light taken out from the light-taking out surface such as the side surface of the substrate 3 is increased.

In manufacturing the infrared LED element 1 shown in fig. 6, the first electrode 22 may be patterned during the execution of the step S5. More specifically, after a resist mask patterned by photolithography is formed, a material (e.g., AuGe/Ni/Au) for forming the first electrode 22 is formed into a film by a vacuum evaporation apparatus, and the resist mask is peeled off by peeling. Then, the first electrode 22 was formed by applying an alloying treatment (annealing treatment) by a heating treatment at 450 ℃ for 10 minutes. Since the subsequent steps are common to the above embodiment, the description thereof will be omitted.

With the infrared LED element 1 shown in fig. 6, in the case of die bonding on the stem 35 via the silver paste 34 as in fig. 3I, the silver paste 34 enters into the void B2 illustrated in fig. 6. As a result, a large refractive index difference between the substrate 3 and the gap B2 as described above is no longer obtained. However, since the silver particles contained in the silver paste 34 that have entered the gap B2 have a high reflectance with respect to infrared light, the function of reflecting light traveling in the-Z direction in the substrate 3 toward the + Z direction can be achieved.

In the infrared LED element 1 shown in fig. 6, since the step is formed on the first surface 3a side of the substrate 3, the first electrode 22 and the package substrate may be connected by soldering when mounted. As the brazing, AuSn, SnAgSu, or the like can be used. In this case, since the gap B2 remains, a large refractive index difference can be provided between the substrate 3 and the gap B2 as described above, and therefore, light traveling in the-Z direction in the substrate 3 can be easily totally reflected on the first surface 3 a.

<2> in fig. 6, the reflective layer 25 may be formed in the region B2 where the first electrode 22 is not formed (see fig. 7).

The reflective layer 25 may be made of a material having a high reflectance with respect to infrared light of 1000nm or more and less than 1800nm, and may be made of, for example, Ag alloy, Au, Al, or the like. These materials are both highly reflective to infrared light compared to the material of the first electrode 22. The reflectance of the reflective layer 25 with respect to infrared light is preferably 50% or more, and more preferably 70% or more.

In manufacturing the infrared LED element 1 shown in fig. 7, the patterned first electrode 22 and the patterned reflective layer 25 may be formed separately during the execution of the above-described step S5.

<3> in fig. 6, the dielectric layer 26 may be formed in the region B2 where the first electrode 22 is not formed (see fig. 8).

Dielectric layer 26 may be made of a material having a refractive index lower than that of substrate 3 made of InP, for example, SiO₂、SiN、Al₂O₃ITO, ZnO, etc. Since these materials all have a refractive index smaller than that of InP by 0.2 or more, a refractive index difference is realized in which total reflection is likely to occur at the interface between substrate 3 and dielectric layer 26.

In manufacturing the infrared LED element 1 shown in fig. 8, the patterned first electrode 22 and the patterned dielectric layer 26 may be formed separately during the execution of the above-described step S5. For example, by plasma CVD method₂After the dielectric layer 26 having the above-described structure is formed on the entire surface, a resist mask patterned by photolithography is used to perform wet etching treatment with a BHF solution, thereby performing patterning treatment of the dielectric layer 26. Then, the first electrode 22 is formed in the opening region of the dielectric layer 26.

The infrared LED element 1 shown in fig. 8 can be mounted by the method of step S11 as described above. In this case, since the silver paste 34 is sandwiched between the lower layers of the dielectric layers 26, the Ag particles contained in the silver paste 34 function as a reflective member.

Further, as shown in fig. 9, the reflective layer 25 may be formed so as to cover the dielectric layer 26 and the surface of the first electrode 22.

<4> in the above embodiment, the explanation was made on the assumption that the uneven portion 41 is formed on the side surface of the substrate 3 provided in the infrared LED element 1. However, the substrate 3 may not necessarily have the concave-convex portion 41 on the side surface (see fig. 10). In this case, as shown in fig. 10, the uneven portion 42 may not be formed on the side surface of the semiconductor layer 10.

<5> in the infrared LED element 1 described in the above embodiment, the surface of the second semiconductor layer 14, which is the light extraction surface parallel to the XY plane, among the surfaces of the semiconductor layers 10, may be formed with a concave-convex portion.

<6> in the above embodiment, a case where the second semiconductor layer 14 as a p-type contact layer is formed on the upper surface of the second semiconductor layer 13 as a p-type cladding layer, and the second electrode 21 is formed on the surface of the second semiconductor layer 14 has been described. However, the conductivity type of the contact layer may be n-type as long as it is in contact with the second electrode 21. In this case, the second electrode 21 is formed on the upper layer of the second semiconductor layer 13 via an n-type contact of a thin film.

Description of the reference symbols

1: infrared LED element

3: substrate

3 a: first surface of the substrate

3 b: second surface of the substrate

10: semiconductor layer

11: first semiconductor layer

12: active layer

13. 14: a second semiconductor layer

21: second electrode

22: a first electrode

23: pad electrode

24: pad electrode

25: reflective layer

26: dielectric layer

28: passivation film

31: dicing sheet

34: silver paste

35: tube holder

41: concave-convex part

42: concave-convex part