GaN-based LED epitaxial structure, preparation method thereof and LED chip

Abstract

The application provides a GaN-based LED epitaxial structure and a preparation method and an LED chip thereof. The electron blocking layer reduces electron leakage, and a hole injection layer containing a thin AlN layer is arranged between a multi-quantum well layer and the electron blocking layer in the epitaxial structure. The hole injection layer not only reduces the height of the potential barrier during hole transport, but also provides an effective path for hole tunneling and increases the energy during hole injection, thereby significantly improving the hole injection efficiency, increasing the hole concentration injected into the multi-quantum well layer, and further increasing the light-emitting efficiency of the LED.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, in particular to a GaN-based LED epitaxial structure and a preparation method thereof, and an LED chip. Background Art

[0002] The GaN-based LED structure includes a buffer layer, an undoped GaN layer, an N-type nitride semiconductor layer, a multi-quantum well layer, an electron blocking layer, a P-type nitride semiconductor layer, and a P-type ohmic contact layer, stacked in sequence. To address electron overflow, an AlInGaN or AlInGaN / GaN SL is often used as an electron blocking layer (EBL) between the multi-quantum well layer and the P-type nitride semiconductor layer. This prevents electrons from leaking into the P-type nitride semiconductor layer and non-radiatively recombine with holes. While traditional EBLs can reduce electron leakage into the P-type nitride semiconductor layer, they also hinder the injection of holes from the P-type nitride semiconductor layer into the multi-quantum well layer, hindering hole injection into the multi-quantum well layer. Moreover, since most GaN-based LED epitaxy grows along the GaN

[0001] polarity direction, polarization-induced positive charge will be generated at the interface between the last quantum barrier and the EBL due to lattice mismatch, which increases the valence band barrier height and reduces the hole concentration in the EBL, further limiting hole injection. Summary of the Invention

[0003] In order to overcome the above shortcomings, the present invention provides a GaN-based LED epitaxial structure and a preparation method thereof, and an LED chip, which effectively solves the problem of low hole injection efficiency caused by the electron blocking layer in the epitaxial structure.

[0004] The technical solution provided by the present invention is:

[0005] On the one hand, the present invention provides a GaN-based LED epitaxial structure, comprising: a buffer layer, an undoped GaN layer, an N-type nitride semiconductor layer, a multi-quantum well layer, a hole injection layer, an electron blocking layer, a P-type nitride semiconductor layer and a P-type ohmic contact layer sequentially formed on the surface of the growth substrate; wherein the hole injection layer comprises a first AlN layer, a first AlN layer, and a P-type ohmic contact layer sequentially formed on the surface of the multi-quantum well layer. x In y Ga z N layer, second AlN layer, second Al a In b Ga c N layer, z=1-xy, c=1-ab, the thickness of the first AlN layer is 1nm~3nm, the thickness of the second AlN layer is 0.5nm~2nm; the thickness of the second AlN layer is 0.5nm~2nm; a In b Ga cThe Mg doping concentration in the N layer is 5×10 19 / cm 3 to 3×10 20 / cm 3 .

[0006] On the other hand, the present invention provides a method for preparing a GaN-based LED epitaxial structure, comprising the following steps: sequentially growing a buffer layer, an undoped GaN layer, an N-type nitride semiconductor layer, a multi-quantum well layer, a hole injection layer, an electron blocking layer, a P-type nitride semiconductor layer, and a P-type ohmic contact layer on the surface of a growth substrate; wherein,

[0007] The hole injection layer includes a first AlN layer, a first AlN layer, and a x In y Ga z N layer, second AlN layer, second Al a In b Ga c N layer, z=1-xy, c=1-ab, the thickness of the first AlN layer is 1nm~3nm, the thickness of the second AlN layer is 0.5nm~2nm; the thickness of the second AlN layer is 0.5nm~2nm; a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 to 3×10 20 / cm 3 .

[0008] In another aspect, the present invention provides an LED chip, which includes the above-mentioned GaN-based LED epitaxial structure.

[0009] The GaN-based LED epitaxial structure and its preparation method, as well as the LED chip provided by the present invention, reduce electron leakage through the electron blocking layer. At the same time, a hole injection layer comprising a thin AlN layer is used between the multi-quantum well layer and the electron blocking layer in the epitaxial structure. This not only reduces the potential barrier height during hole transport, but also provides an effective path for hole tunneling and increases the energy during hole injection, significantly improving the hole injection efficiency and increasing the hole concentration injected into the multi-quantum well layer, thereby increasing the luminous efficiency of the LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of the epitaxial structure of a GaN-based LED in one embodiment of the present invention;

[0011] Figure 2 Schematic diagram of a hole injection layer of a GaN-based LED epitaxial structure according to one embodiment of the present invention;

[0012] Figure 3 A schematic diagram of part of the energy band of an LED epitaxial structure in the prior art;

[0013] Figure 4 A schematic diagram of part of the energy bands of a GaN-based LED epitaxial structure according to an embodiment of the present invention;

[0014] Figure 5 A schematic diagram of part of the energy bands of a GaN-based LED epitaxial structure in another embodiment of the present invention;

[0015] Figure 6 This is a flow chart of preparing a GaN-based LED epitaxial structure in one embodiment of the present invention.

[0016] Reference numerals:

[0017] 1-growth substrate, 2-buffer layer, 3-undoped GaN layer, 4-N-type nitride semiconductor layer, 5-multi-quantum well layer, 51-quantum well layer, 52-quantum barrier layer, 6-hole injection layer, 61-first AlN layer, 62-first Al x In y Ga z N layer, 63-second AlN layer, 64-second Al a In b Ga c N layer, 65-third AlN layer, 7-electron blocking layer, 8-P-type nitride semiconductor layer, 9-P-type ohmic contact layer. DETAILED DESCRIPTION

[0018] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0019] The first embodiment of the present invention is a GaN-based LED epitaxial structure, comprising: a buffer layer 2, an undoped GaN layer 3, an N-type nitride semiconductor layer 4, a multi-quantum well layer 5, a hole injection layer 6, an electron blocking layer 7, a P-type nitride semiconductor layer 8 and a P-type ohmic contact layer 9 sequentially formed on the surface of a growth substrate 1; wherein the hole injection layer comprises a first AlN layer 61, a first AlN layer 62, a first AlN layer 63, a first AlN layer 64, a first AlN layer 65, a first AlN layer 66, a first AlN layer 67, a first AlN layer 68, a first AlN layer 69, a first AlN layer 70, a first AlN layer 71, a first AlN layer 72, a first AlN layer 73, a first AlN layer 74, a first AlN layer 75, a first AlN layer x In y Ga z N layer 62, second AlN layer 63, second Al a In b Ga cN layer 64, z = 1-xy, c = 1-ab, the thickness of the first AlN layer is 1nm~3nm, the thickness of the second AlN layer is 0.5nm~2nm; the thickness of the second AlN layer is 0.5nm~2nm; a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 to 3×10 20 / cm 3 ; The electron blocking layer 7 is Al d In e Ga f In the N layer, f=1-de, the Al component content d gradually decreases along the epitaxial growth direction.

[0020] like Figure 1 and Figure 2 As shown, the growth substrate 1 used in this embodiment is a sapphire (0002) substrate or a silicon (111) substrate; the entire GaN-based LED epitaxial structure is grown on the surface of the sapphire substrate along the

[0002] polarity direction or on the surface of the silicon substrate along the

[111] polarity direction. The buffer layer 2 is any one of AlN, AlGaN, and GaN, with a thickness between 10nm and 50nm, which is beneficial to reducing the interface defects between the substrate and the subsequently grown GaN. The undoped GaN layer 3 is an unintentionally doped GaN structure with a thickness of 0.2μm to 4μm. The N-type nitride semiconductor layer 4 is an n-type GaN doped with Si with a thickness between 1μm and 4μm, and the Si doping concentration is 1×10 18 / cm 3 to 3×10 19 / cm 3 , acting as a source of electrons. When voltage is applied to the epitaxial structure, electrons generated in the N-type nitride semiconductor layer are injected into the multi-quantum well layer 5, where they radiatively recombine with holes, generating photons. The multi-quantum well layer 5 is where electrons and holes radiatively recombine. To achieve radiative recombination and luminescence, electrons and holes are injected into the multi-quantum well layer from the N-type nitride semiconductor layer 4 and the P-type nitride semiconductor layer 8, respectively.

[0021] In this embodiment, the multi-quantum well layer 5 is a periodic structure of InGaN quantum well layers and AlGaN quantum barrier layers, with the number of periods being 5-15. In each period, the thickness of the InGaN quantum well layer is 2nm-4nm, and the thickness of the AlGaN quantum barrier layer is 5nm-15nm. Except for the last quantum barrier layer (the quantum barrier layer close to the hole injection layer), the Al content in the AlGaN quantum barrier layer of each period is 0-5%, and the Si doping concentration is 1×10 17 / cm 3 to 2×10 18 / cm3 The Al content in the last AlGaN quantum barrier layer in contact with the hole injection layer is 0-20%, and no Si doping is performed. That is, the AlGaN quantum barrier layer in contact with the first AlN layer in the multi-quantum well layer is an AlGaN quantum barrier layer, and this AlGaN quantum barrier layer is not doped with Si. In order to prevent electrons from overflowing the multi-quantum well layer, the Al component content of the last AlGaN quantum barrier layer is higher than that of the other quantum barrier layers, forming a larger transport barrier.

[0022] The hole injection layer 6, located between the multi-quantum well layer and the electron blocking layer, comprises a thin AlN layer. This provides a tunneling path for holes and creates band bending, increasing the energy during hole injection and significantly improving hole injection efficiency. For an AlN layer that is too thick, the probability of hole tunneling decreases significantly, resulting in a decrease in luminescence efficiency. However, if the AlN layer is too thin, the resulting band bending offset is too small to effectively increase the energy during hole injection. Therefore, the thickness should be determined based on a comprehensive consideration of the degree of band bending and the hole tunneling efficiency.

[0023] In order to improve the hole injection efficiency in this embodiment, a first AlN layer, a first AlN layer and a second AlN layer are sequentially stacked in the hole injection layer. x In y Ga z N layer, second AlN layer, second Al a In b Ga c N layer, z=1-xy, c=1-ab, the thickness of the first AlN layer is 1nm~3nm, and the thickness of the second AlN layer is 0.5nm~2nm; through Al x In y Ga z N separates the first AlN layer from the second AlN layer. Not only can each AlN layer enable hole tunneling injection, but the band bending effect generated by the two AlN layers is superimposed, further increasing the energy during hole injection and effectively improving the hole injection efficiency. x In y Ga z In the N layer, 0<=x<0.3, 0<=y<0.1, and the thickness is 0.5nm-1.5nm, that is, the Al component content is less than 0.3, and the In component content is less than 0.1. The second Al a In b Ga c In the N layer, 0<=a<0.2, 0<=b<0.1, and the Mg doping concentration is 5×10 19 / cm 3 to 3×10 20 / cm 3 , that is, the Al component content is less than 0.2, the In component content is less than 0.1, and Mg doping is performed.

[0024] To better describe the band bending caused by the AlN layer, refer to Figure 3 and Figure 4 Schematic diagram of energy bands, showing the energy bands from the quantum well layer 5 (for convenience, only two quantum barrier layers 52 and one quantum well layer 51 are shown in the figure, and it should be understood that there are other quantum well layers and quantum barrier layers not shown in the entire epitaxial structure) to the P-type nitride semiconductor layer 8 (from left to right) in the traditional LED epitaxial structure and the epitaxial structure of this embodiment. In each figure, the upper part is the conduction band of the corresponding structure, and the lower part is the valence band of the corresponding structure.

[0025] Figure 3 In the LED epitaxial structure shown (existing technology), only a second Al layer is formed between the last quantum barrier layer 52 of the multi-quantum well layer 5 (including the quantum well layer 51 and the quantum barrier layer 52) and the electron blocking layer 7. a In b Ga c N layer 64, there is no AlN layer. Observing the change trend of the valence band, starting from the P-type nitride semiconductor layer 8 and going left, it is easy to see that the electron blocking layer 7 itself causes a significant increase in the valence band, forming a valence band barrier. The valence band first gradually increases through the electron blocking layer 7 and the second Al a In b Ga c After the N layer 64 is lowered, it reaches the multi-quantum well layer. In general, the valence band height difference between the P-type nitride semiconductor layer 8 at the starting point of the hole and the valence band height difference between the end point quantum well layer 51 is small, the energy during hole injection is low, and the hole injection efficiency is low.

[0026] Figure 4 In the LED epitaxial structure shown in FIG, the hole injection layer (including the first AlN layer 61, the first Al x In y Ga z N layer 62, second AlN layer 63, second Al a In b Ga c N layer 64) is formed between the last quantum barrier layer 52 of the multi-quantum well layer 5 (including the quantum well layer 51 and the quantum barrier layer 52) and the electron blocking layer 7. Observing the valence band, it can be seen that after the band bending offset of the first AlN layer 61 and the second AlN layer 63 is superimposed, the valence band height difference between the P-type nitride semiconductor layer 8 at the starting point of the hole and the quantum well layer 51 at the end point is significantly improved, and the energy of hole injection is effectively improved. In addition, the thinner first AlN layer 61 and the second AlN layer 63 facilitate the tunneling of holes, providing a second path for holes to be injected into the quantum well layer. Therefore, compared with the Figure 3The structure shown can effectively improve the hole injection efficiency.

[0027] At the same time, in the electron blocking layer 7, Al d In e Ga f The Al content d of the N layer (f = 1-de) gradually decreases along the epitaxial growth direction (towards the P-type nitride semiconductor layer), and 0 <d<0.5,0<=e<0.1,即Al组分含量总体小于0.5,In组分含量小于0.1。电子阻挡层可以是单层结构也可以是多个叠层结构,如一实例中,电子阻挡层由两个Al组分含量递减的AlGaN叠层组成,其中,靠近空穴注入层一侧的AlGaN中,Al组分含量为0.1-0.3,靠近P型氮化物半导体层一侧的AlGaN中,Al组分含量为0.005-0.04。只要能有效阻挡电子溢出,并形成Al组分含量递减的结构即可,本实施例对此不做限制。

[0028] The P-type nitride semiconductor layer 8 is a Mg-doped GaN layer or an AlGaN layer, and the Mg doping concentration is 5×10 18 -5×10 20 / cm 3 , with a thickness of 5nm-150nm. The P-type ohmic contact layer 9 is highly doped, and is also a Mg-doped GaN layer or AlGaN layer, but the Mg doping concentration is greater than the doping concentration in the P-type nitride semiconductor layer 8. The Mg doping concentration is between 5×10 19 -5×10 20 / cm 3 between.

[0029] The above embodiment is improved to obtain this embodiment. In this embodiment, Figure 5 As shown, a third AlN layer is formed between the hole injection layer and the electron blocking layer. The thickness of the third AlN layer is 0.5nm-2.5nm, that is, the first AlN layer 61, the first AlN layer 62 and the first AlN layer 63 are sequentially stacked on the multi-quantum well layer. x In y Ga z N layer 62, second AlN layer 63, second Al a In b Ga cThe N layer 64 and the third AlN layer 65 have a total of five stacked layers. In one example, the third AlN layer is 1.5 nm. The third AlN layer also facilitates the tunneling of holes, and the resulting energy band bending offset is further superimposed with other AlN layers. Overall, the valence band height of the P-type nitride semiconductor layer 8 at the starting point of the hole is significantly greater than the valence band height of the end point quantum well layer 51, further increasing the energy during hole injection. In addition, the third AlN layer causes the upward bending of the valence band of the electron blocking layer to decrease, thereby reducing the valence band barrier height of the hole from the P-type nitride semiconductor layer to the electron blocking layer, thereby further improving the hole injection efficiency.

[0030] In this example, 57 mil × 57 mil flip-chip LEDs were fabricated under the same conditions using LED epitaxial structures with different hole injection layer thicknesses. The relative light intensity (LOP), operating voltage (VF), and power conversion efficiency (WPE) of these LEDs were measured at a current of 350 mA, and the data were normalized. The experimental results are shown in the following table:

[0031] Among them, sample A is a comparative example, sample B is the sample of the previous embodiment, and samples C1-C11 are samples of this embodiment. The values ​​of relative light intensity (LOP), working voltage (VF), and photoelectric conversion efficiency (WPE) in the table are normalized based on sample A, that is, the actual values ​​are divided by the corresponding values ​​of sample A.

[0032] Sample A has only a second Al layer formed between the multi-quantum well layer and the electron blocking layer. a In b Ga c N layer, band structure and Figure 3 Correspondingly, the second Al a In b Ga c The thickness of the N layer is 25 nm. As can be seen from the above table, the relative light intensity and photoelectric conversion efficiency of the other samples are higher than those of sample A.

[0033] Sample B has a 3 nm first AlN layer and a 1 nm first AlN layer formed between the multi-quantum well layer and the electron blocking layer. x In y Ga z N layer, a 1nm second AlN layer and a 25nm second Al a In b Ga c N layer, band structure and Figure 4Correspondingly, the light intensity (LOP) increased by 2.41% and the photoelectric conversion efficiency (WPE) increased by 1.55% compared to sample A. The first and second AlN layers cause the band bending offset, increasing the energy during hole injection and providing an effective path for hole tunneling, effectively improving the hole injection efficiency, thereby improving light intensity and photoelectric conversion efficiency.

[0034] Sample C1 is further processed in the second Al based on sample B. a In b Ga c A third AlN layer of 1.5 nm is formed on the N layer, and the band structure is similar to Figure 5 Correspondingly, the data in the table show that compared with sample A, the light intensity LOP increased by 2.92% and the light intensity LOP increased by 1.99%. The introduction of the third AlN layer further improved the light intensity LOP and the photoelectric conversion efficiency WPE. The third AlN layer in sample C can also provide a hole tunneling path due to its thin thickness. Figure 5 It is easy to see from the energy band shown that the third AlN layer bends the valence band barrier of the electron blocking layer 7, and the valence band of the electron blocking layer close to the third AlN decreases upward. Figure 4 The energy band shown in sample B reduces the valence band barrier height of holes from the P-type nitride semiconductor layer to the electron blocking layer, and the band bending offset caused by the third AlN layer is superimposed on the band bending offset generated by the first and second AlN layers, further improving the energy during hole injection, effectively improving the hole injection efficiency, thereby increasing the luminous efficiency of the LED.

[0035] In order to obtain the optimal thickness combination of each structure in the hole injection layer, 11 groups of samples (C1-C11) were further designed for testing, among which:

[0036] The thickness of the first AlN layer in C1-C5 gradually decreases from 3.0nm to 1.0nm. Except for the first AlN layer, the thickness of other layers are the same. Analysis of these five sets of test data shows that when the thickness of the first AlN layer is 2.0nm, the light intensity LOP and the photoelectric conversion efficiency WPE are the largest. On this basis, whether the thickness of the first AlN layer increases or decreases, the light intensity LOP and the photoelectric conversion efficiency WPE will decrease. As mentioned above, if the thickness of the AlN layer is too thick, the probability of hole tunneling will be greatly reduced, resulting in a decrease in luminous efficiency. If the thickness of the AlN layer is too thin, the band bending offset caused will be too small to effectively improve the hole transmission energy.

[0037] The first Al in C3, C9, C10, and C11 x In y Ga z The thickness of the N layer gradually increases from 0.5nm to 2.0nm, except for the first Alx In y Ga z Except for the N layer, the thickness of other layers is the same. Analysis of these four test data shows that when the first Al x In y Ga z When the thickness of the N layer is 1.0 nm, the light intensity LOP is the largest, and the first Al x In y Ga z The N layer has the best photoelectric conversion efficiency when its thickness is 1.5nm. Since the thickness of this layer affects the magnitude of the polarization electric field at the interface, it should not be set too thick or too thin.

[0038] The thickness of the second AlN layer in C3, C6, C7, and C8 gradually increases from 0.5nm to 2.0nm. Except for the second AlN layer, the thicknesses of the other layers are the same. Analysis of these four sets of test data shows that when the thickness of the second AlN layer is 1.0nm, the light intensity LOP and the photoelectric conversion efficiency WPE are the largest. On this basis, whether the thickness of the second AlN layer increases or decreases, the light intensity LOP and the light intensity WPE will decrease. As mentioned above, if the thickness of the AlN layer is too thick, the probability of hole tunneling will be greatly reduced, resulting in a decrease in luminous efficiency. If the thickness of the AlN layer is too thin, the band bending offset caused will be too small and the hole transmission energy cannot be effectively improved.

[0039] The best sample obtained from the table is C3, and the thickness of each layer in the hole injection layer is: 2.0nm first AlN layer, 1nm first Al x In y Ga z N layer, a 1nm second AlN layer and a 25nm second Al a In b Ga c The N layer and the 1.5nm thick third AlN layer are stacked in sequence. Compared with sample A, the light intensity LOP of the obtained sample is increased by 3.45% and the photoelectric conversion efficiency WPE is increased by 3.23%.

[0040] Another embodiment of the present invention is a method for preparing a GaN-based LED epitaxial structure, such as Figure 6 As shown,

[0041] First, a growth substrate is provided, and then the following steps are included: a buffer layer, an undoped GaN layer, an N-type nitride semiconductor layer, a multi-quantum well layer, a hole injection layer, an electron blocking layer, a P-type nitride semiconductor layer and a P-type ohmic contact layer are sequentially grown on the surface of the growth substrate; wherein the hole injection layer includes a first AlN layer, a first AlN layer, and a P-type ohmic contact layer formed on the surface of the multi-quantum well layer in sequence. x In y Ga zN layer, second AlN layer, second Al a In b Ga c N layer, z = 1-xy, c = 1-ab, the thickness of the first AlN layer is 1nm~3nm, the thickness of the second AlN layer is 0.5nm~2nm; the thickness of the second AlN layer is 0.5nm~2nm; a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 to 3×10 20 / cm 3 ;

[0042] The electron blocking layer is Al d In e Ga f In the N layer, f=1-de, the Al component content d gradually decreases along the epitaxial growth direction.

[0043] The growth substrate used in this embodiment is a sapphire (0002) substrate or a silicon (111) substrate; the entire GaN-based LED epitaxial structure is grown on the surface of the sapphire substrate along the

[0002] polarity direction or on the surface of the silicon substrate along the

[111] polarity direction. The buffer layer is any one of AlN, AlGaN, and GaN, with a thickness between 10nm and 50nm, which is beneficial to reducing the interface defects between the substrate and the subsequently grown GaN. The undoped GaN layer is an unintentionally doped GaN structure with a thickness of 0.2μm to 4μm. The N-type nitride semiconductor layer is an n-type GaN doped with Si with a thickness between 1μm and 4μm, and the Si doping concentration is 1×10 18 / cm 3 to 3×10 19 / cm 3 , which provides electrons. When voltage is applied to the epitaxial structure, electrons generated in the N-type nitride semiconductor layer are injected into the multi-quantum well layer, where they undergo radiative recombination with holes, generating photons. The multi-quantum well layer is where electrons and holes undergo radiative recombination. To achieve radiative recombination and light emission, electrons and holes are injected into the multi-quantum well layer from the N-type nitride semiconductor layer and the P-type nitride semiconductor layer, respectively.

[0044] In this embodiment, the multi-quantum well layer is a periodic structure of InGaN quantum well layers and AlGaN quantum barrier layers, with the number of periods being 5-15. In each period, the thickness of the InGaN quantum well layer is 2nm-4nm, and the thickness of the AlGaN quantum barrier layer is 5nm-15nm. Except for the last quantum barrier layer (the quantum barrier layer close to the hole injection layer), the Al content in the AlGaN quantum barrier layer of each period is 0-5%, and the Si doping concentration is 1×10 17 / cm 3 to 2×10 18 / cm 3 The last AlGaN quantum barrier layer in contact with the hole injection layer has an Al content of 0-20% and is not doped with Si. That is, the AlGaN quantum barrier layer in contact with the first AlN layer in the multi-quantum well layer is not doped with Si.

[0045] The hole injection layer is located between the multi-quantum well layer and the electron blocking layer, and is provided with a thin AlN layer, which can provide a hole tunneling path and cause band bending, thereby increasing the energy during hole injection and significantly improving the hole injection efficiency. For the AlN layer, if the thickness is too thick, the probability of hole tunneling will be greatly reduced, resulting in a decrease in luminous efficiency. If it is too thin, the band bending offset caused by it will be too small and will not be able to effectively increase the energy during hole injection. The thickness needs to be set by comprehensively considering the degree of band bending and the hole tunneling injection efficiency. In this embodiment, in order to improve the hole injection efficiency, a first AlN layer, a first AlN layer, and a second AlN layer are formed in the hole injection layer. x In y Ga z N layer, second AlN layer, second Al a In b Ga c N layer, z=1-xy, c=1-ab, the thickness of the first AlN layer is 1nm~3nm, and the thickness of the second AlN layer is 0.5nm~2nm; through Al x In y Ga z N separates the first AlN layer from the second AlN layer. Not only can each AlN layer enable hole tunneling injection, but the band bending effect generated by the two AlN layers is superimposed, further increasing the energy during hole injection and effectively improving the hole injection efficiency. x In y Ga z In the N layer, 0<=x<0.3, 0<=y<0.1, and the thickness is 0.5nm-1.5nm, that is, the Al component content is less than 0.3, and the In component content is less than 0.1. The second Al a In b Ga c In the N layer, 0<=a<0.2, 0<=b<0.1, and the Mg doping concentration is 5×10 19 / cm 3 to 3×10 20 / cm 3 , that is, the Al component content is less than 0.2, the In component content is less than 0.1, and Mg doping is performed.

[0046] At the same time, in the electron blocking layer, Al dIn e Ga f The Al component content d of the AlN layer (f = 1 - d - e) gradually decreases along the epitaxial growth direction, and 0 < d < 0.5, 0 <= e < 0.1, that is, the total Al component content is less than 0.5, and the In component content is less than 0.1. The electron blocking layer can be a single layer structure or a plurality of stacked structures. In an example, the electron blocking layer is composed of two AlGaN layers with decreasing Al component content, wherein the Al component content of the AlGaN layer close to the hole injection layer is 0.1-0.3, and the Al component content of the AlGaN layer close to the P-type nitride semiconductor layer is 0.005-0.04. As long as the electron overflow can be effectively blocked and a structure with decreasing Al component content is formed, the present embodiment does not limit this. The P-type nitride semiconductor layer is a Mg-doped GaN layer or an AlGaN layer, and the Mg doping concentration is 5x10 18 -5x10 20 / cm 3 , and the thickness is 5nm-150nm. The P-type ohmic contact layer 9 is highly doped, and is also a Mg-doped GaN layer or an AlGaN layer, but the Mg doping concentration is greater than that in the P-type nitride semiconductor layer 8, and the Mg doping concentration is between 5x10 19 -5x10 20 / cm 3 .

[0047] The above embodiment is improved to obtain the present embodiment. In the present embodiment, a third AlN layer is further formed between the hole injection layer and the electron blocking layer. The thickness of the third AlN layer is 0.5nm-2.5nm, that is, the first AlN layer 61, the first Al x In y Ga z N layer 62, the second AlN layer 63, the second Al a In b Ga c N layer 64, and the third AlN layer 65 are sequentially stacked on the surface of the multiple quantum well layer, forming a structure of five layers in total. The third AlN layer also facilitates the tunneling of holes, and the energy band bending offset generated by the third AlN layer is further superimposed on the energy band bending offsets generated by the other AlN layers. Overall, the valence band height of the P-type nitride semiconductor layer 8 at the starting point of the holes is significantly greater than the valence band height of the terminal quantum well layer 51, further increasing the energy of the holes during injection. In addition, the third AlN layer causes the valence band of the electron blocking layer to bend upward, reducing the valence band barrier height of the holes from the P-type nitride semiconductor layer to the electron blocking layer, and further improving the hole injection efficiency.

[0048] Another embodiment of the present invention provides an LED chip comprising the aforementioned GaN-based LED epitaxial structure. It should be understood that, because the epitaxial structure of this LED chip includes a novel hole injection layer between the multi-quantum well layer and the electron blocking layer, the hole injection efficiency is effectively enhanced, thereby improving the luminous efficiency of the LED chip.

[0049] During the LED chip fabrication process, a GaN-based LED epitaxial structure is etched to form a light-emitting unit. A first electrode and a second electrode are then fabricated on the light-emitting unit. The first electrode is conductively connected to the N-type nitride semiconductor layer in the light-emitting unit, and the second electrode is conductively connected to the P-type nitride semiconductor layer in the light-emitting unit. The epitaxial structure is etched according to predetermined LED dimensions, with the specific dimensions designed based on actual application requirements. The fabrication process includes etching the GaN-based LED epitaxial structure using ICP dry etching technology and fabricating the first and second electrodes. The first and second electrodes can be located on the same side of the light-emitting unit (forming a flip-chip or face-up structure) or on different sides (forming a vertical structure). Regardless of the design of the first and second electrodes, they must ensure that they do not affect light output. Thus, external current is conducted into the LED chip through the first and second electrodes. In other embodiments, the LED chip may also include structures such as a bonding layer, a reflective layer, a passivation layer, a connecting metal layer, and a transparent conductive layer to enhance the chip's luminescence. This is not a limitation in this embodiment; as long as the LED chip can emit light normally, the design is sufficient.

[0050] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A GaN-based LED epitaxial structure, characterized in that: include: A buffer layer, an undoped GaN layer, an N-type nitride semiconductor layer, a multi-quantum well layer, a hole injection layer, an electron blocking layer, a P-type nitride semiconductor layer and a P-type ohmic contact layer are sequentially formed on the surface of the growth substrate; wherein, The hole injection layer includes a first AlN layer, a first AlN layer, and a x In y Ga z N layer, second AlN layer, second Al a In b Ga c N layer, z=1-xy, c=1-ab, the thickness of the first AlN layer is 1nm~3nm, the thickness of the second AlN layer is 0.5nm~2nm; the thickness of the second AlN layer is 0.5nm~2nm; a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 to 3×10 20 / cm 3 , the first Al x In y Ga z The thickness of the N layer is 0.5nm-1.5nm, and the second Al a In b Ga c The thickness of the N layer is 25 nm.

2. The GaN-based LED epitaxial structure according to claim 1, wherein: A third AlN layer is formed between the hole injection layer and the electron blocking layer. The thickness of the third AlN layer is 0.5 nm to 2.5 nm.

3. The GaN-based LED epitaxial structure according to claim 1 or 2, wherein: The multi-quantum well layer is a periodic structure of InGaN quantum well layer and AlGaN quantum barrier layer, and the number of periods is 5-15; The Al content in the last AlGaN quantum barrier layer in contact with the hole injection layer is 0~20%. Except for the last quantum barrier layer, the Al content in each period of AlGaN quantum barrier layer is 0~5%, and the Si doping concentration is 1×10 17 / cm 3 to 2×10 18 / cm 3 .

4. The GaN-based LED epitaxial structure according to claim 1 or 2, wherein: The first Al x In y Ga z In layer N, 0<=x<0.3, 0<=y<0.

1.

5. The GaN-based LED epitaxial structure according to claim 1 or 2, wherein: The second Al a In b Ga c In the N layer, 0<=a<0.2, 0<=b<0.

1.

6. The GaN-based LED epitaxial structure according to claim 1 or 2, wherein: The electron blocking layer is Al d In e Ga f In the N layer, f=1-de, the Al component content d gradually decreases along the epitaxial growth direction.

7. The GaN-based LED epitaxial structure according to claim 6, wherein: The electron blocking layer Al d In e Ga f N, 0 <d<0.5,0<=e<0.1。 8. A method for preparing a GaN-based LED epitaxial structure, characterized in that: The following steps are involved: A buffer layer, an undoped GaN layer, an N-type nitride semiconductor layer, a multi-quantum well layer, a hole injection layer, an electron blocking layer, a P-type nitride semiconductor layer and a P-type ohmic contact layer are sequentially grown on the surface of the growth substrate; wherein, The hole injection layer includes a first AlN layer, a first AlN layer, and a x In y Ga z N layer, second AlN layer, second Al a In b Ga c N layer, z=1-xy, c=1-ab, the thickness of the first AlN layer is 1nm~3nm, the thickness of the second AlN layer is 0.5nm~2nm; the thickness of the second AlN layer is 0.5nm~2nm; a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 to 3×10 20 / cm 3 , the first Al x In y Ga z The thickness of the N layer is 0.5nm-1.5nm, and the second Al a In b Ga c The thickness of the N layer is 25 nm.

9. The method for preparing a GaN-based LED epitaxial structure according to claim 8, wherein: A third AlN layer is formed between the hole injection layer and the electron blocking layer. The thickness of the third AlN layer is 0.5 nm to 2.5 nm.

10. An LED chip, characterized in that: The LED chip includes the GaN-based LED epitaxial structure according to any one of claims 1 to 7.

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