阅读说明：本技术 一种紫外发光二极管外延结构 (Ultraviolet light emitting diode epitaxial structure ) 是由 王孟源 曾伟强 于 2019-08-20 设计创作，主要内容包括：本发明公开了一种紫外发光二极管外延结构,包括依次设于衬底上的AlN层、N型AlGaN层、渐变层、有源层、阻挡层和P型AlGaN层。本发明通过渐变层和阻挡层来提升外延结构的晶体质量,提高发光效率。(The invention discloses an ultraviolet light-emitting diode epitaxial structure which comprises an AlN layer, an N-type AlGaN layer, a graded layer, an active layer, a barrier layer and a P-type AlGaN layer which are sequentially arranged on a substrate. The invention improves the crystal quality of the epitaxial structure and the luminous efficiency through the gradient layer and the barrier layer.)

1. An ultraviolet light emitting diode epitaxial structure is characterized by comprising an AlN layer, an N-type AlGaN layer, a graded layer, an active layer, a barrier layer and a P-type AlGaN layer which are sequentially arranged on a substrate,

the gradient layer consists of N N-type AlGaN layers, N is more than or equal to 4 and less than or equal to 9, and the Al contents of the AlGaN layers of the 1 st layer and the N-th layer are the same;

if n is singular, the Al content of the AlGaN layers from the 1 st layer to the (n +1)/2 nd layer is gradually reduced, and the Al content of the AlGaN layers from the (n +1)/2 nd layer to the nth layer is gradually increased;

if n is a double number, the Al content of the AlGaN layers from the 1 st layer to the n/2 nd layer is gradually reduced, and the Al content of the AlGaN layers from the n/2 nd layer to the n nd layer is gradually increased;

the barrier layer is formed by a first AlGaN layer, a first Mg layer, a second AlGaN layer, a third Mg layer and a fourth Mg layer in an alternating mode, and the content of Al in the first AlGaN layer is different from that of Al in the second AlGaN layer.

2. The ultraviolet light emitting diode epitaxial structure according to claim 1, wherein the graded layer is composed of N-type AlGaN layers, x of the 1 st and nth layers is 0.5 to 0.6, and x of the 2 nd to (N-1) th layers is 0.2 to 0.4.

3. The ultraviolet light emitting diode epitaxial structure of claim 1, wherein the Mg content in the first Mg layer is greater than the Mg content in the second Mg layer, and the Mg content in the third Mg layer is greater than the Mg content in the fourth Mg layer.

4. The epitaxial structure of claim 1, wherein the doping concentration of Mg in the barrier layer is 1-2E 19atom/cm³。

5. The ultraviolet light emitting diode epitaxial structure of any one of claims 1 to 4, wherein the barrier layer is prepared by the following method:

(1) introducing a nitrogen source with the flow rate of 60-70 slm, an aluminum source with the flow rate of 150-180 sccm and a gallium source with the flow rate of 25-30 sccm, and growing a first AlGaN layer with the thickness of 1-10 nm;

(2) closing an aluminum source and a gallium source, introducing a nitrogen source with the flow rate of 60-70 slm and a magnesium source with the flow rate of 900-1000 sccm, and continuing for 4-10 minutes to form a first Mg layer; introducing a nitrogen source with the flow rate of 50-60 slm and a magnesium source with the flow rate of 800-900 sccm, and continuing for 1-5 minutes to form a second Mg layer;

(3) closing the magnesium source, introducing a nitrogen source with the flow rate of 60-70 slm, an aluminum source with the flow rate of 150-180 sccm and a gallium source with the flow rate of 25-30 sccm, and growing a second AlGaN layer with the thickness of 1-10 nm;

(4) closing an aluminum source and a gallium source, introducing a nitrogen source with the flow rate of 60-70 slm and a magnesium source with the flow rate of 900-1000 sccm, and continuing for 4-10 minutes to form a third Mg layer; introducing a nitrogen source with the flow rate of 50-60 slm and a magnesium source with the flow rate of 800-900 sccm, and continuing for 1-5 minutes to form a fourth Mg layer;

(5) repeating the steps (1), (2), (3) and (4) for a plurality of times.

6. The ultraviolet light emitting diode epitaxial structure of claim 1, wherein a buffer layer is arranged between the AlN layer and the N-type AlGaN layer, the buffer layer is composed of an AlN/AlGaN superlattice structure with m periods, and m is more than or equal to 3.

7. The UV LED epitaxial structure of claim 6, wherein the buffer layer is made of m periods of AlN/Al_uGa_1-uN type superlatticeThe lattice structure is formed, and u is less than 0.8; each of AlN/Al_uGa_1-uThe thickness of the N superlattice structure is 2-10 nm; the thickness of the buffer layer is 200-400 nm.

8. The epitaxial structure of claim 1, wherein the active layer is composed of 5-9 periods of quantum well structure comprising Al_xGa_1-xN well layer and Al_yGa_1-yAnd (3) N barrier layers, wherein x is more than 0 and less than 0.3, and y is more than 40% larger than x.

Technical Field

The invention relates to the technical field of light emitting diodes, in particular to an ultraviolet light emitting diode epitaxial structure.

Background

The AlGaN semiconductor material has a very wide direct band gap, the forbidden band width is continuously adjustable from 3.4-6.2 eV, and the photoresponse waveband of the AlGaN semiconductor material is enabled to cover from near Ultraviolet (UVA) to deep Ultraviolet (UVC). Compared with the traditional ultraviolet light source such as a mercury lamp and a xenon lamp, the ultraviolet LED has the advantages of no mercury pollution, controllable wavelength, small volume, low power consumption, long service life and the like, and has wide application prospect and great market demand in the fields of high color rendering index white light illumination, anti-counterfeiting identification, ultraviolet polymer curing, sterilization, medical sanitation, water and air purification, high-density optical data storage and the like.

Compared with a mature GaN-based blue light epitaxial structure, the ultraviolet light emitting diode epitaxial structure has generally low luminous efficiency, and the luminous efficiency is sharply reduced along with the reduction of the wavelength. How to prepare an ultraviolet light emitting diode epitaxial structure with good crystallization quality and high luminous power is a problem which is urgently needed to be solved at present.

Disclosure of Invention

The invention aims to solve the technical problem of providing an ultraviolet light emitting diode epitaxial structure which is good in crystal quality and high in light emitting efficiency.

In order to solve the above technical problems, the present invention provides an epitaxial structure of an ultraviolet light emitting diode, comprising an AlN layer, an N-type AlGaN layer, a graded layer, an active layer, a barrier layer, and a P-type AlGaN layer sequentially disposed on a substrate,

the gradient layer consists of N N-type AlGaN layers, N is more than or equal to 4 and less than or equal to 9, and the Al contents of the AlGaN layers of the 1 st layer and the N-th layer are the same;

if n is singular, the Al content of the AlGaN layers from the 1 st layer to the (n +1)/2 nd layer is gradually reduced, and the Al content of the AlGaN layers from the (n +1)/2 nd layer to the nth layer is gradually increased;

if n is a double number, the Al content of the AlGaN layers from the 1 st layer to the n/2 nd layer is gradually reduced, and the Al content of the AlGaN layers from the n/2 nd layer to the n nd layer is gradually increased;

the barrier layer is formed by a first AlGaN layer, a first Mg layer, a second AlGaN layer, a third Mg layer and a fourth Mg layer in an alternating mode, and the content of Al in the first AlGaN layer is different from that of Al in the second AlGaN layer.

In a further improvement of the above aspect, the graded layer is composed of N-type AlGaN layers, where x in the 1 st and nth layers is 0.5 to 0.6, and x in the 2 nd to (N-1) th layers is 0.2 to 0.4.

As an improvement of the above, the content of Mg in the first Mg layer is larger than the content of Mg in the second Mg layer, and the content of Mg in the third Mg layer is larger than the content of Mg in the fourth Mg layer.

As an improvement of the scheme, the doping concentration of Mg in the barrier layer is 1-2E 19atom/cm³。

As an improvement of the above aspect, the barrier layer is prepared by the following method:

(1) introducing a nitrogen source with the flow rate of 60-70 slm, an aluminum source with the flow rate of 150-180 sccm and a gallium source with the flow rate of 25-30 sccm, and growing a first AlGaN layer with the thickness of 1-10 nm;

(2) closing an aluminum source and a gallium source, introducing a nitrogen source with the flow rate of 60-70 slm and a magnesium source with the flow rate of 900-1000 sccm, and continuing for 4-10 minutes to form a first Mg layer; introducing a nitrogen source with the flow rate of 50-60 slm and a magnesium source with the flow rate of 800-900 sccm, and continuing for 1-5 minutes to form a second Mg layer;

(3) closing the magnesium source, introducing a nitrogen source with the flow rate of 60-70 slm, an aluminum source with the flow rate of 150-180 sccm and a gallium source with the flow rate of 25-30 sccm, and growing a second AlGaN layer with the thickness of 1-10 nm;

(4) closing an aluminum source and a gallium source, introducing a nitrogen source with the flow rate of 60-70 slm and a magnesium source with the flow rate of 900-1000 sccm, and continuing for 4-10 minutes to form a third Mg layer; introducing a nitrogen source with the flow rate of 50-60 slm and a magnesium source with the flow rate of 800-900 sccm, and continuing for 1-5 minutes to form a fourth Mg layer;

(5) repeating the steps (1), (2), (3) and (4) for a plurality of times.

As an improvement of the scheme, a buffer layer is arranged between the AlN layer and the N-type AlGaN layer and consists of AlN/AlGaN superlattice structures with m periods, and m is more than or equal to 3.

As a modification of the above, the buffer layer is made of AlN/Al of m periods_uGa_1-uN superlattice structure, u is less than 0.8; each of AlN/Al_uGa_1-uThe thickness of the N superlattice structure is 2-10 nm; the thickness of the buffer layer is 200-400 nm.

As an improvement of the scheme, the active layer is composed of a quantum well structure with 5-9 periods, and the quantum well structure comprises Al_xGa_1-xN well layer and Al_yGa_1-yAnd (3) N barrier layers, wherein x is more than 0 and less than 0.3, and y is more than 40% larger than x.

The implementation of the invention has the following beneficial effects:

the invention provides an ultraviolet light-emitting diode epitaxial structure which comprises an AlN layer, an N-type AlGaN layer, a graded layer, an active layer, a barrier layer and a P-type AlGaN layer which are sequentially arranged on a substrate.

According to the invention, the buffer layer is formed between the AlN layer and the N-type AlGaN layer, so that stress generated by lattice mismatch is gradually released in the buffer layer, the cracking problem of the AlN layer is avoided, the quality of the AlN layer is improved, dislocation and defects are greatly reduced, the crystal quality of an epitaxial structure is improved, and the luminous efficiency is improved. In addition, lower dislocation and defect of the epitaxial material mean fewer photon capture centers, more ultraviolet light can pass through the epitaxial structure to emit light outwards, the light emitting efficiency is improved, the total heat generated after the photons are captured is reduced, and the performance of the violet LED device is greatly improved.

The barrier layer is formed by alternately forming a first AlGaN layer, a first Mg layer, a second AlGaN layer, a third Mg layer and a fourth Mg layer. According to the invention, no Mg impurity is introduced into the first AlGaN layer and the second AlGaN layer, so that stacking dislocation is not formed, the crystallization quality of the P-type GaN layer is effectively improved, and the dislocation density is reduced.

The content of Al in the first AlGaN layer and the content of Al in the second AlGaN layer must be different, so that the difference of potential epitaxy can be generated, and the energy band of the barrier layer can be bent. The invention improves the doping concentration of Mg by changing the energy band bending of the barrier layer. The doping concentration of Mg in the barrier layer can reach 1-2E 19atom/cm³The doping concentration of Mg in the existing electron blocking layer is only 1E18 atom/cm³。

Drawings

Fig. 1 is a schematic structural view of an epitaxial structure of the present invention.

FIG. 2 is a process diagram of the growth of the barrier layer of the present invention;

fig. 3 is a diagram of a conventional barrier layer growth process.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.

Referring to fig. 1, the ultraviolet light emitting diode epitaxial structure provided by the present invention includes an AlN layer 20, an N-type AlGaN layer 40, a graded layer 50, an active layer 60, a barrier layer 70, and a P-type AlGaN layer 80, which are sequentially disposed on a substrate 10.

The material of the substrate 10 of the present invention may be sapphire, silicon carbide, or silicon, or may be other semiconductor materials. Preferably, the substrate 10 of the present invention is a sapphire substrate.

The AlN layer 20 of the present invention is made of AlN as a base material for the epitaxial structure, and functions to prepare the N-type AlGaN layer 40, the active layer 60, and the P-type AlGaN layer 80 for subsequent growth. Because the energy level of AlN is the largest in a III/V system and the light absorption to the LED is the smallest, the AlN is used as a base material to effectively improve the light extraction efficiency of the epitaxial structure.

Preferably, the AlN layer 20 has a thickness of 2 to 4 μm. If the thickness of the AlN layer 20 is less than 2 mu m, the stress mismatch between the substrate and the AlN material cannot be completely released, and the crystal quality of the AlN material is influenced; if the thickness is too thick, time and material are wasted.

Since the AlN layer 20 and the N-type AlGaN layer 40 have a large lattice difference therebetween, if the N-type AlGaN layer is directly grown on the AlN layer, there is a problem that stress is concentrated at the interface between the two materials to cause cracking. According to the invention, the buffer layer 30 is arranged between the AlN layer 20 and the N-type AlGaN layer 40, so that stress generated by lattice mismatch is gradually released from the buffer layer 30, the cracking problem of the AlN layer is avoided, the quality of the AlN layer is improved, dislocation and defects are greatly reduced, the crystal quality of an epitaxial structure is improved, and the luminous efficiency is improved. In addition, lower dislocation and defect of the epitaxial material mean fewer photon capture centers, more ultraviolet light can pass through the epitaxial structure to emit light outwards, the light emitting efficiency is improved, the total heat generated after the photons are captured is reduced, and the performance of the violet LED device is greatly improved.

Preferably, the thickness of the buffer layer is 200-400 nm. If the thickness of the buffer layer is less than 200nm, stress is not well released and dislocation is reduced, and if the thickness is too thick, time and materials are wasted.

The AlN/AlGaN superlattice structure can well release stress between an AlN material and N-type AlGaN, and in addition, the AlN/AlGaN superlattice structure can bend dislocation lines, so that the aim of improving the crystal quality is fulfilled. Specifically, the buffer layer 30 is made of AlN/Al with m periods_uGa_1-uN (u is less than 0.8) superlattice structure, and m is more than or equal to 3. Note that if u is larger than 0.8, the buffer layer cannot release stress well.

Each of AlN/Al_uGa_1-uThe thickness of the N superlattice structure is 2-10 nm, and the thickness of the N superlattice structure is several atomic layers, so that the AlN/Al is_uGa_1-uThe N superlattice structure is best for stress relief and dislocation reduction.

The gradient layer 40 is composed of N N-type AlGaN layers, N is more than or equal to 4 and less than or equal to 9, and the Al contents of the AlGaN layers of the 1 st layer and the N-th layer are the same; if n is singular, the Al content of the AlGaN layers from the 1 st layer to the (n +1)/2 nd layer is gradually reduced, and the Al content of the AlGaN layers from the (n +1)/2 nd layer to the nth layer is gradually increased; if n is a double number, the Al content of the AlGaN layers from the 1 st layer to the n/2 nd layer gradually decreases, and the Al content of the AlGaN layers from the n/2 nd layer to the n nd layer gradually increases.

The gradient layer can effectively inhibit quantum confinement Stark effect, weaken the polarization electric field of the active layer and finally improve the internal quantum efficiency of the ultraviolet LED chip. Because the graded layer is arranged between the active layer and the N-type AlGaN layer, the influence on the active layer which is not grown can be reduced, so that the migration of Al components in the active layer is reduced, the change of an energy band structure in the active layer can be avoided, and the luminous efficiency of an epitaxial structure is improved

Preferably, the graded layer is composed of N-type AlGaN layers, x of the 1 st and nth layers is 0.5 to 0.6, and x of the 2 nd to (N-1) th layers is 0.2 to 0.4.

In order to improve the light extraction efficiency of the active layer 60, the structure of the active layer is specially designed. The active layer 60 is composed of a quantum well structure with 5-9 periods, and the quantum well structure comprises Al_xGa_1-xN well layer and Al_yGa_1-yAnd (3) N barrier layers, wherein x is more than 0 and less than 0.3, and y is more than 40% larger than x.

It should be noted that too few quantum wells cannot completely limit the electron and hole pairs, which affects brightness; too many quantum well cycles do not increase brightness but time and raw material costs increase due to the limited mobility distance of the holes.

As the light-emitting wavelength of the epitaxial structure is determined by x in the quantum well structure, the corresponding Al component of the ultraviolet light-emitting diode with the wavelength of 260-320 nm is 0-30%, namely x is more than 0 and less than 0.3. To better limit the emission of electron-hole pairs in a quantum well structure, y needs to be more than 40% larger than x.

The N-type AlGaN layer 40 of the present invention is used to supply electrons and the P-type AlGaN layer 80 is used to supply holes. In order to improve the light extraction efficiency of the epitaxial structure, the doping concentration of the N-type AlGaN layer is 2E19atom/cm³(ii) a The doping concentration of the P-type AlGaN is 2E20atom/cm³。

According to the invention, the barrier layer 50 is arranged between the active layer 40 and the P-type GaN layer 60, so that the effects of blocking current and improving current expansion are achieved, the hole concentration and the mobility of the P-type GaN layer can be improved, more hole-electron pairs are provided for the active layer, the recombination probability is improved, the brightness is improved, and the photoelectric property of the epitaxial structure is improved.

The barrier layer is formed by alternately forming a first AlGaN layer, a first Mg layer, a second AlGaN layer, a third Mg layer and a fourth Mg layer, wherein the content of Al in the first AlGaN layer is different from that in the second AlGaN layer, the content of Mg in the first Mg layer is greater than that in the second Mg layer, and the content of Mg in the third Mg layer is greater than that in the fourth Mg layer. According to the invention, no Mg impurity is introduced into the first AlGaN layer and the second AlGaN layer, so that stacking dislocation is not formed, the crystallization quality of the P-type GaN layer is effectively improved, and the dislocation density is reduced.

The content of Al in the first AlGaN layer and the content of Al in the second AlGaN layer must be different, so that the difference of potential epitaxy can be generated, and the energy band of the barrier layer can be bent. The invention improves the doping concentration of Mg by changing the energy band bending of the barrier layer.

In addition, the content of Mg in the first Mg layer provided in the first AlGaN layer and the second AlGaN layer is larger than the content of Mg in the second Mg layer, so that the doping concentration of Mg can be further increased. The doping concentration of Mg in the barrier layer can reach 1-2E 19atom/cm³The doping concentration of Mg in the existing electron blocking layer is only 1E18 atom/cm³The efficiency of Mg for activating holes is generally about 1% of the Mg doping concentration, and holes are more easily excited with higher doping concentrations.

The thickness of the first AlGaN layer is 1-10 nm, and the thickness of the second AlGaN layer is 1-10 nm. Preferably, the thickness of the first AlGaN layer is 2-6 nm, and the thickness of the second AlGaN layer is 2-6 nm. According to the invention, the doping concentration is improved by changing the energy band bending of the barrier layer, and the piezoelectric polarization of the superlattice layer is weakened due to the fact that the thickness of the first AlGaN layer or the second AlGaN layer is too thin and too thick, so that the energy band bending is reduced, and Mg doping is not facilitated.

Referring to fig. 2, the barrier layer of the present invention is prepared by the following method:

(1) introducing a nitrogen source with the flow rate of 60-70 slm, an aluminum source with the flow rate of 150-180 sccm and a gallium source with the flow rate of 25-30 sccm, and growing a first AlGaN layer with the thickness of 1-10 nm;

(2) closing an aluminum source and a gallium source, introducing a nitrogen source with the flow rate of 60-70 slm and a magnesium source with the flow rate of 900-1000 sccm, and continuing for 4-10 minutes to form a first Mg layer; introducing a nitrogen source with the flow rate of 50-60 slm and a magnesium source with the flow rate of 800-900 sccm, and continuing for 1-5 minutes to form a second Mg layer;

(3) closing the magnesium source, introducing a nitrogen source with the flow rate of 60-70 slm, an aluminum source with the flow rate of 150-180 sccm and a gallium source with the flow rate of 25-30 sccm, and growing a second AlGaN layer with the thickness of 1-10 nm;

(4) closing an aluminum source and a gallium source, introducing a nitrogen source with the flow rate of 60-70 slm and a magnesium source with the flow rate of 900-1000 sccm, and continuing for 4-10 minutes to form a third Mg layer; introducing a nitrogen source with the flow rate of 50-60 slm and a magnesium source with the flow rate of 800-900 sccm, and continuing for 1-5 minutes to form a fourth Mg layer;

(5) repeating the steps (1), (2), (3) and (4) for a plurality of times.

Preferably, steps (1), (2), (3) and (4) are repeated 3 to 9 times.

The nitrogen source is preferably NH₃The aluminum source is TMAl, the gallium source is TMGa, and the magnesium source is Cp₂And Mg. Preferably, the flow rate of the gallium source in the step (3) is smaller than that of the gallium source in the step (1).

Referring to fig. 3, in the conventional barrier layer, a nitrogen source, an aluminum source, a gallium source and a magnesium source are simultaneously introduced, and a competitive relationship of combination of Mg, Al, Ga and N exists, and in the steps (2) and (4), only the nitrogen source and the magnesium source are introduced to form a first Mg layer, a second Mg layer, a third Mg layer and a fourth Mg layer, so that the competitive relationship does not exist, and the doping efficiency of the Mg element is improved.

In the process of growing the first AlGaN layer and the second AlGaN layer by using an intermittent doping mode, because no Mg impurity is introduced, stacking dislocation cannot be formed, so that the crystal quality of the barrier layer is improved, the crystallization quality of the P-type GaN layer is improved, and the dislocation density is reduced.

In addition, the discontinuous doping mode of the invention utilizes the different potential difference of the first AlGaN layer and the second AlGaN layer to promote the energy band bending of the barrier layer. According to the invention, the doping concentration of Mg is improved by changing the energy band bending of the barrier layer, so that the hole concentration and the mobility of the P-type GaN layer are improved.

It is noted that the present invention increases the doping concentration by increasing the material quality of the barrier layer and improving its band structure so that most of the Mg impurities are below the fermi level.

In order to obtain a band-bending barrier layer, the Al component content in step (1) and step (3) cannot be the same. Because the doping rates of Mg in AlGaN with different Al contents are different, the duration setting of the step (2) and the step (4) is also different. The higher the Al component content, the more difficult the Mg is doped, and the longer the time is required. If the content of the Al component in the step (1) is greater than that in the step (3), the duration in the step (2) is longer than that in the step (4).

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.