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

Abstract

According to the GaN-based LED epitaxial structure, the preparation method thereof and the LED chip provided by the invention, electron leakage is reduced through the electron blocking layer, and meanwhile, the hole injection layer comprising the thin AlN layer is adopted between the multi-quantum well layer and the electron blocking layer in the epitaxial structure, so that the barrier barrier height during hole transport can be reduced, and the hole transport efficiency can be improved. In addition, an effective path for hole tunneling is provided, energy during hole injection is increased, hole injection efficiency is remarkably improved, the concentration of holes injected into the multi-quantum well layer is increased, and then the luminous efficiency of the LED is improved.

Description

Technical Field

[0001] The 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] In the GaN-based LED structure, there are buffer layers, undoped GaN layers, N-type nitride semiconductor layers, multi-quantum well layers, electron blocking layers, P-type nitride semiconductor layers, and P-type ohmic contact layers stacked in sequence. In order to improve the electron overflow problem, 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 to prevent electrons from crossing the multi-quantum well layer region and leaking into the P-type nitride semiconductor layer to non-radiatively recombine with holes. Although the traditional EBL can reduce the leakage of electrons into the P-type nitride semiconductor layer, it also hinders the injection of holes from the P-type nitride semiconductor layer into the multi-quantum well layer, which is not conducive to the injection of holes into the multi-quantum well layer. Moreover, since most GaN-based LED epitaxy grows along the GaN

[0001] polarity direction, polarization-induced positive charges will be generated at the interface between the last quantum barrier and the EBL due to lattice mismatch, increasing the valence band barrier height and reducing 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: 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 a 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 Al a In b Ga c The Mg doping concentration in the N layer is 5×1019 / cm 3 Up to 3×10 20 / cm 3 .

[0005] 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, 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 Al a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 Up to 3×10 20 / cm 3 .

[0006] In yet another aspect, the present invention provides an LED chip, which includes the above-mentioned GaN-based LED epitaxial structure.

[0007] The GaN-based LED epitaxial structure and preparation method thereof, and LED chip provided by the present invention reduce electron leakage through an electron blocking layer. At the same time, a hole injection layer including a thin AlN layer is used between the multi-quantum well layer and the electron blocking layer in the epitaxial structure, which not only reduces the potential barrier height during hole transport, but also provides an effective path for hole tunneling, increases the energy during hole injection, significantly improves the hole injection efficiency, increases the hole concentration injected into the multi-quantum well layer, and thus increases the luminous efficiency of the LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A schematic diagram of a GaN-based LED epitaxial structure in one embodiment of the present invention; Figure 2 A schematic diagram of a hole injection layer of a GaN-based LED epitaxial structure in one embodiment of the present invention; Figure 3 A schematic diagram of some energy bands of LED epitaxial structures in the prior art; Figure 4 A schematic diagram of a portion of the energy bands of a GaN-based LED epitaxial structure in one embodiment of the present invention; Figure 5 A schematic diagram of a portion of the energy bands of a GaN-based LED epitaxial structure in another embodiment of the present invention; Figure 6 The figure is a flow chart of preparing a GaN-based LED epitaxial structure in one embodiment of the present invention.

[0009] Reference numerals: 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

[0010] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings and other implementation methods can be obtained based on these drawings without creative work.

[0011] 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, which are sequentially formed on the surface of a growth substrate 1; wherein the hole injection layer comprises a first AlN layer 61, a first Al x In y Ga z N layer 62, second AlN layer 63, second Al a In b Ga c N 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 5×1019 / cm 3 Up 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.

[0012] 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 reduce 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-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 Up to 3×10 19 / cm 3 , plays the role of providing electrons. After applying voltage to the epitaxial structure, the electrons generated by the N-type nitride semiconductor layer are injected into the multi-quantum well layer 5 to undergo radiation recombination with holes, thereby generating photons. The multi-quantum well layer 5 is a place where electrons and holes undergo radiation recombination. In order to achieve radiation 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.

[0013] In this embodiment, the multi-quantum well layer 5 is a periodic structure of an InGaN quantum well layer and an AlGaN quantum barrier layer, and the number of periods is 5-15; in each period, the thickness of the InGaN quantum well layer is 2nm-4nm, the thickness of the AlGaN quantum barrier layer is 5nm-15nm, and 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 Up to 2×10 18 / cm 3The 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 the AlGaN quantum barrier layer is not Si doped. 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 other quantum barrier layers, forming a larger transport barrier.

[0014] The hole injection layer 6 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, increase the energy during hole injection, and significantly improve 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 cannot 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.

[0015] 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. 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 Up 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.

[0016] To better describe the band bending caused by the AlN layer, refer to Figure 3 and Figure 4 The energy band diagram shows 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 conventional LED epitaxial structure and the epitaxial structure of the present embodiment. In each figure, the upper one is the conduction band of the corresponding structure, and the lower one is the valence band of the corresponding structure.

[0017] Figure 3 In the LED epitaxial structure shown in the figure (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 to the left, it is easy to know that the electron blocking layer 7 itself causes a significant increase in the valence band, forming a valence band barrier. The valence band first passes through the electron blocking layer 7 and gradually increases and then the second Al a In b Ga c The N layer 64 is lowered to reach the multi-quantum well layer, and overall, the valence band height difference between the P-type nitride semiconductor layer 8 at the hole starting point and the valence band height difference between the terminal quantum well layer 51 is small, the energy of hole injection is low, and the hole injection efficiency is low.

[0018] Figure 4 In the LED epitaxial structure shown in the figure, 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), 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. By observing the valence band, it can be seen that after the energy 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 end point quantum well layer 51 is significantly improved, the energy of hole injection is effectively improved, and the thin 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, so relative to Figure 3The shown structure can effectively improve the hole injection efficiency.

[0019] Meanwhile, in the electron blocking layer 7, the Al content d of the Al d In e Ga f N layer (f = 1 - d - e) gradually decreases along the epitaxial growth direction (the direction towards the P-type nitride semiconductor layer), and 0 < d < 0.5, 0 <= e < 0.1, that is, the overall Al content is less than 0.5 and the In content is less than 0.1. The electron blocking layer can be a single-layer structure or a multi-stack structure. For example, in one instance, the electron blocking layer is composed of two AlGaN stacks with decreasing Al content. Among them, in the AlGaN closer to the hole injection layer, the Al content is 0.1 - 0.3, and in the AlGaN closer to the P-type nitride semiconductor layer, the Al content is 0.005 - 0.04. As long as it can effectively block the electron overflow and form a structure with decreasing Al content, this embodiment does not limit it.

[0020] The P-type nitride semiconductor layer 8 is a Mg-doped GaN layer or AlGaN layer, and the Mg doping concentration is 5×10 18 -5×10 20 / cm 3 , and the thickness is 5 nm - 150 nm. 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 that in the P-type nitride semiconductor layer 8, and the Mg doping concentration is between 5×10 19 -5×10 20 / cm 3 .

[0021] This embodiment is obtained by improving the above embodiment. In this embodiment, as Figure 5 shown, between the hole injection layer and the electron blocking layer, a third AlN layer is further formed, and the thickness of the third AlN layer is 0.5 nm - 2.5 nm. That is, on the multi-quantum well layer, a first AlN layer 61, a first Al x In y Ga z N layer 62, a second AlN layer 63, and a 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 1.5nm. 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 electron blocking layer valence band to bend upward less, reducing the valence band barrier height from the P-type nitride semiconductor layer to the electron blocking layer, thereby further improving the hole injection efficiency.

[0022] In this embodiment, the LED epitaxial structure with different thickness values ​​constituting the hole injection layer is used to produce a flip-chip LED with a size of 57mil×57mil under the same conditions. The relative light intensity (LOP), working voltage (VF) and photoelectric conversion efficiency (WPE) of the above LED are tested at a current of 350mA, and the data are normalized. The experimental results are shown in the following table: 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.

[0023] Sample A has only a second Al 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. It can be seen from the above table that the relative light intensity and photoelectric conversion efficiency of the other samples are higher than those of sample A.

[0024] 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 with sample A. The first AlN layer and the second AlN layer cause the band bending offset, increase the energy during hole injection, and provide an effective way for hole tunneling, effectively improving the hole injection efficiency, thereby improving the light intensity and photoelectric conversion efficiency.

[0025] 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, it can be seen from the data in the table 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 thinner thickness. Analysis Figure 5 It is easy to see from the energy bands shown that the third AlN layer causes the valence band barrier of the electron blocking layer 7 to bend, and the valence band of the electron blocking layer close to the third AlN layer decreases upward. Figure 4 As for the energy band shown in sample B, the valence band barrier height of holes from the P-type nitride semiconductor layer to the electron blocking layer is reduced, 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, which further increases the energy during hole injection, effectively improving the hole injection efficiency, thereby increasing the luminous efficiency of the LED.

[0026] 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: 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 5 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 luminescence efficiency. If the thickness of the AlN layer is too thin, the band bending offset will be too small and the hole transmission energy cannot be effectively improved.

[0027] 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 Al x Iny 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 will affect the polarization electric field of the interface, it should not be set too thick or too thin.

[0028] 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 thickness of 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 will be too small and the hole transmission energy cannot be effectively improved.

[0029] 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 N layer, and a 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%.

[0030] Another embodiment of the present invention is a method for preparing a GaN-based LED epitaxial structure, such as Figure 6 As shown, A growth substrate is provided first, 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 sequentially on the surface of the multi-quantum well layer. x In y Ga z N layer, second AlN layer, second Al a Inb 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 1nm~3nm. a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 Up to 3×10 20 / cm 3 ; 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.

[0031] 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 reduce 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-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 Up to 3×10 19 / cm 3 , plays the role of providing electrons. After applying voltage to the epitaxial structure, the electrons generated by the N-type nitride semiconductor layer are injected into the multi-quantum well layer to undergo radiative recombination with holes, thereby generating photons. The multi-quantum well layer is a place where electrons and holes undergo radiative recombination. In order to achieve radiative recombination and luminescence, 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.

[0032] In this embodiment, 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; in each period, the thickness of the InGaN quantum well layer is 2nm-4nm, the thickness of the AlGaN quantum barrier layer is 5nm-15nm, and 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 Up to 2×10 18 / cm3 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.

[0033] 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, increase the energy during hole injection, and significantly improve 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 cannot 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 stacked in sequence. 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. 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 Up 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.

[0034] At the same time, in the electron blocking layer, Al d In e Ga fFor the N layer (f = 1 - d - e), the Al composition content d gradually decreases along the epitaxial growth direction, and 0 < d < 0.5, 0 <= e < 0.1, that is, the overall Al composition content is less than 0.5, and the In composition content is less than 0.1. The electron blocking layer can be a single-layer structure or a multi-stack structure. In one example, the electron blocking layer is composed of two AlGaN stacks with decreasing Al composition content. Among them, in the AlGaN closer to the hole injection layer, the Al composition content is 0.1 - 0.3, and in the AlGaN closer to the P-type nitride semiconductor layer, the Al composition content is 0.005 - 0.04. As long as it can effectively block the electron overflow and form a structure with decreasing Al composition content, this embodiment does not limit it. The P-type nitride semiconductor layer is a Mg-doped GaN layer or AlGaN layer, and the Mg doping concentration is 5×10 18 -5×10 20 / cm 3 , and the thickness is 5 nm - 150 nm. The P-type ohmic contact layer 9 is highly doped and is also a Mg-doped GaN layer or AlGaN layer, but the doping concentration of Mg is greater than that in the P-type nitride semiconductor layer 8, and the Mg doping concentration is between 5×10 19 -5×10 20 / cm 3 .

[0035] This embodiment is obtained by improving the above embodiment. In this 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 0.5 nm - 2.5 nm, that is, a structure with five stacked layers of 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 is stacked in sequence on the surface of the multi-quantum well layer. The third AlN layer also facilitates the tunneling of holes, and the energy band bending shift generated is further superimposed with other AlN layers. Generally speaking, 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 terminal quantum well layer 51, further increasing the energy during hole injection. In addition, the third AlN layer causes the valence band of the electron blocking layer to bend upward less, reducing the valence band barrier height from the P-type nitride semiconductor layer to the electron blocking layer for holes, and further improving the hole injection efficiency.

[0036] Another embodiment of the present invention is an LED chip, wherein the LED chip includes the above-mentioned GaN-based LED epitaxial structure. It should be understood that since a novel hole injection layer is formed between the multi-quantum well layer and the electron blocking layer in the epitaxial structure of the LED chip, the hole injection efficiency is effectively enhanced, thereby improving the luminous efficiency of the LED chip.

[0037] In the process of preparing the LED chip, the GaN-based LED epitaxial structure is etched to form a light-emitting unit; and the first electrode and the second electrode are made 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 the predetermined LED size, and the specific size can be designed according to the actual application requirements. The preparation process includes etching the GaN-based LED epitaxial structure using ICP dry etching technology, and also includes the preparation of the first electrode and the second electrode. The first electrode and the second electrode can be located on the same side of the light-emitting unit (forming a flip-chip structure or a face-up structure), or on different sides of the light-emitting unit (forming a vertical structure); no matter how the positions of the first electrode and the second electrode are designed, it is sufficient to ensure that they do not affect the light output, so that the external current is conducted to the LED chip through the first electrode and the second electrode. In addition, in other embodiments, a bonding layer, a reflective layer, a passivation layer, a connecting metal layer, a transparent conductive layer and other structures are also formed in the LED chip to enhance the light-emitting effect of the chip. This embodiment does not limit this, as long as the LED chip can emit light normally.

[0038] It should be noted that the above embodiments can be freely combined as needed. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered as the protection scope 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 Al a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 Up to 3×10 20 / cm 3 .

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

3. The GaN-based LED epitaxial structure according to claim 1 or 2, characterized in that: 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 Up to 2×10 18 / cm 3 .

4. The GaN-based LED epitaxial structure according to claim 1 or 2, characterized in that: The first Al 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.

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

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6. The GaN-based LED epitaxial structure according to claim 1 or 2, characterized in that: 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, characterized in that: 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 Al 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 Al a In b Ga c The Mg doping concentration in the N layer is 5×10 19 / cm 3 Up to 3×10 20 / cm 3 .

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

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

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