A high hole injection efficiency epitaxial structure and preparation method thereof

Abstract

The present invention discloses an epitaxial structure with high hole injection efficiency and a preparation method thereof, relating to the technical field of semiconductor devices. The epitaxial structure of the present invention includes a buffer layer, a U-GaN layer, an N-GaN layer, a multi-quantum well light-emitting layer, a P-GaN composite layer and a P-type GaN layer; the P-GaN composite layer includes a first stepped composite layer, a second stepped composite layer and a third stepped composite layer; the first stepped composite layer includes a first InAlN layer and a first InGaN layer; the second stepped composite layer includes a second Mg-doped InAlN layer, a second AlN layer and a second MgN layer; the third stepped composite layer includes a third InAlN layer, a third AlN layer and a third InGaN layer. The present invention can improve the hole injection efficiency of the epitaxial structure and promote the recombination of electrons and holes, thereby improving the luminous efficiency of the chip at low operating current density.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to an epitaxial structure with high hole injection efficiency and a preparation method thereof. Background Art

[0002] As a next-generation display technology, Micro LED, with its advantages of self-luminescence, high brightness, high contrast, low power consumption, and fast response, demonstrates tremendous potential for application in fields such as display, lighting, and virtual reality. It has become a research hotspot and development direction in the optoelectronics field. As market requirements for Micro LED display device performance continue to increase, the luminous efficiency of its core component, the Micro LED chip, has become a key indicator of industry competitiveness.

[0003] At present, in the actual application of Micro LED chips, it is found that when the working current density is 0.01A / cm 2 ~0.5A / cm 2 In this current density range, the chip's luminous efficiency significantly decreases, failing to meet market demand for high-brightness, low-power display products. In-depth research has revealed that this problem is primarily due to the low hole injection efficiency and electron-hole recombination rate of the chip's epitaxial structure. Within this current density range, holes are difficult to effectively inject into the active region to recombine with electrons for emission, resulting in a large accumulation of carriers at the interface. This increases energy loss and reduces luminous efficiency, severely limiting the performance of Micro LED chips at low current densities. Furthermore, low luminous efficiency can cause problems such as chip overheating, further impacting device stability and lifespan.

[0004] Therefore, how to optimize the epitaxial structure of Micro LED chips, improve the hole injection efficiency, and thus improve the chip's performance at 0.01A / cm 2 ~0.5A / cm 2 The luminous efficiency in the current density range has become a key issue that needs to be urgently addressed in the field of Micro LED technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an epitaxial structure with high hole injection efficiency, which can improve the hole injection efficiency and promote the recombination of electrons and holes, thereby improving the luminous efficiency of the Micro LED chip at low operating current density.

[0006] In order to solve the above technical problems, the present invention provides an epitaxial structure with high hole injection efficiency, comprising a buffer layer, a U-GaN layer, an N-GaN layer, a multi-quantum well light-emitting layer, a P-GaN composite layer and a P-type GaN layer stacked in sequence;

[0007] The P-GaN composite layer includes a first stepped composite layer, a second stepped composite layer and a third stepped composite layer stacked in sequence;

[0008] The first stepped composite layer includes a first InAlN layer and a first InGaN layer that are periodically and alternately stacked in sequence;

[0009] The second stepped composite layer includes a second Mg-doped InAlN layer, a second AlN layer, and a second MgN layer that are periodically and alternately stacked in sequence;

[0010] The third stepped composite layer includes a third InAlN layer, a third AlN layer and a third InGaN layer which are periodically and alternately stacked in sequence.

[0011] As an improvement to the above technical solution, the thickness of the first InAlN layer and the first InGaN layer are 1 nm to 5 nm respectively;

[0012] The thicknesses of the second Mg-doped InAlN layer, the second AlN layer and the second MgN layer are 1 nm to 5 nm respectively;

[0013] The thicknesses of the third InAlN layer, the third AlN layer, and the third InGaN layer are 3 nm to 10 nm, respectively.

[0014] As an improvement to the above technical solution, the number of periods of the periodic alternating stacking of the first stepped composite layer is 1 to 3;

[0015] The number of periods of the periodic alternating stacking of the second stepped composite layer is 3 to 5;

[0016] The number of periods of the periodic alternating stacking of the third stepped composite layer is 3 to 5.

[0017] As an improvement to the above technical solution, the Mg doping concentration in the second Mg-doped InAlN layer is 5×10 18 atoms / cm 3 ~5×10 19 atoms / cm 3 , and along the growth direction of the second stepped composite layer, the Mg doping concentration decreases layer by layer.

[0018] As an improvement of the above technical solution, along the growth direction of the second stepped composite layer, the Mg doping concentration of the second Mg-doped InAlN layer in the nth period is C 1. The Mg doping concentration of the second Mg-doped InAlN layer in the n+1th period is C 2, where n is 1, 2, 3, or 4;

[0019] C 1 andC 2 satisfies the following formula: C 2=(0.68~0.85) C 1.

[0020] As an improvement of the above technical solution, the proportions of Al components in the first InAlN layer, the second Mg-doped InAlN layer and the third InAlN layer are respectively 0.1-0.8.

[0021] As an improvement of the above technical solution, the multi-quantum well light-emitting layer includes InGaN quantum well layers and AlGaN quantum barrier layers that are periodically and alternately stacked in sequence, and the number of alternating stacking periods is 5 to 20;

[0022] The InGaN quantum well layer has an In component ratio of 0.01 to 0.3 and a thickness of 2 nm to 5 nm.

[0023] The AlGaN quantum barrier layer has an Al component ratio of 0.01-0.1 and a thickness of 5 nm-15 nm.

[0024] As an improvement to the above technical solution, the P-type GaN layer is doped with Mg, and the Mg doping concentration is 1×10 19 atoms / cm 3 ~1×10 21 atoms / cm 3 ;

[0025] The thickness of the P-type GaN layer is 10 nm to 50 nm.

[0026] Accordingly, the present invention also provides a method for preparing an epitaxial structure with high hole injection efficiency, comprising the following steps:

[0027] (1) Growing a buffer layer on the substrate;

[0028] (2) Growing a U-GaN layer on the buffer layer;

[0029] (3) Growing an N-GaN layer on the U-GaN layer;

[0030] (4) Growing a multi-quantum well light-emitting layer on the N-GaN layer;

[0031] (5) Growing a P-GaN composite layer on the multi-quantum well light-emitting layer;

[0032] (6) Growing a P-type GaN layer on the P-GaN composite layer;

[0033] The P-GaN composite layer includes a first stepped composite layer, a second stepped composite layer and a third stepped composite layer stacked in sequence;

[0034] The first stepped composite layer includes a first InAlN layer and a first InGaN layer that are periodically and alternately stacked in sequence; the second stepped composite layer includes a second Mg-doped InAlN layer, a second AlN layer, and a second MgN layer that are periodically and alternately stacked in sequence; and the third stepped composite layer includes a third InAlN layer, a third AlN layer, and a third InGaN layer that are periodically and alternately stacked in sequence.

[0035] As an improvement of the above technical solution, in step (5), the growth temperature of the P-GaN composite layer is 600° C. to 1000° C., and the growth pressure is 100 torr to 500 torr.

[0036] The implementation of the present invention has the following beneficial effects:

[0037] The present invention improves the epitaxial structure by providing a P-GaN composite layer between the multi-quantum well light-emitting layer and the P-type GaN layer. On the one hand, the InAlN layer in the P-GaN composite layer (i.e., the first InAlN layer, the second Mg-doped InAlN layer, and the third InAlN layer) has a relatively high bandgap, which can effectively block electron mobility, thereby reducing the generation of leakage channels. At the same time, compared with the conventional electron blocking layer (p-AlGaN layer), the lattice mismatch is lower, which improves the subsequent crystal quality and reduces the influence of piezoelectric polarization, which is conducive to increasing the probability of radiative recombination and thus improving the luminous efficiency. On the other hand, while the second stepped composite layer blocks electron overflow, MgN and Mg doping will improve the hole injection efficiency. Mg doping can also reduce the height of the barrier peak that hinders hole injection generated in the valence band due to the influence of piezoelectric polarization, making it easier for holes to be injected into the multi-quantum well light-emitting layer, further improving the luminous efficiency. In addition, a two-dimensional electron gas is formed between the third InAlN layer, the third AlN layer and the third InGaN layer in the third-stage composite layer. The two-dimensional electron gas has a repulsive force on the electrons in the active layer (i.e., the multi-quantum well light-emitting layer), which can effectively confine the electrons in the active layer, promote the effective recombination efficiency between electrons and holes, and thus improve the luminous efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of the high hole injection efficiency epitaxial structure in Example 1 of the present invention;

[0039] Figure 2 yes Figure 1 Schematic diagram of the structure of the P-GaN composite layer in the high hole injection efficiency epitaxial structure shown;

[0040] Among them: substrate 1, buffer layer 2, U-GaN layer 3, N-GaN layer 4, multi-quantum well light-emitting layer 5, P-GaN composite layer 6, P-type GaN layer 7, first stepped composite layer 61, second stepped composite layer 62, third stepped composite layer 63, first InAlN layer 611, first InGaN layer 612, second Mg-doped InAlN layer 621, second AlN layer 622, second MgN layer 623, third InAlN layer 631, third AlN layer 632, third InGaN layer 633. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0042] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product instructions shall be followed.

[0043] like Figure 1 and Figure 2 As shown, this embodiment discloses a high hole injection efficiency epitaxial structure, including a buffer layer 2, a U-GaN layer 3, an N-GaN layer 4, a multi-quantum well light-emitting layer 5, a P-GaN composite layer 6 and a P-type GaN layer 7 stacked in sequence;

[0044] The P-GaN composite layer 6 includes a first stepped composite layer 61, a second stepped composite layer 62 and a third stepped composite layer 63 stacked in sequence;

[0045] The first stepped composite layer 61 includes a first InAlN layer 611 and a first InGaN layer 612 that are periodically and alternately stacked in sequence;

[0046] The second stepped composite layer 62 includes a second Mg-doped InAlN layer 621 , a second AlN layer 622 , and a second MgN layer 623 that are periodically and alternately stacked in sequence;

[0047] The third stepped composite layer 63 includes a third InAlN layer 631 , a third AlN layer 632 , and a third InGaN layer 633 that are periodically and alternately stacked in sequence.

[0048] The present invention improves the epitaxial structure and sets a P-GaN composite layer 6 between the multi-quantum well light-emitting layer 5 and the P-type GaN layer 7. Through the coordinated effect of each layer in the P-GaN composite layer 6, the hole injection efficiency can be effectively improved and the effective recombination between electrons and holes can be promoted, thereby improving the luminous efficiency of the Micro LED chip at low operating current density.

[0049] Specifically, the InAlN layers (i.e., the first InAlN layer 611, the second Mg-doped InAlN layer 621, and the third InAlN layer 631) have a relatively high bandgap, between 2.8 and 4.2 eV. This effectively prevents electron migration, reduces electron mobility, and thus minimizes leakage channels. This allows injected carriers to recombine more efficiently in the active region (i.e., the multi-quantum well light-emitting layer 5), thereby improving the luminous efficiency of the Micro LED chip and increasing the device's light output power. Furthermore, compared to conventional electron-blocking layers (p-AlGaN layers), the InAlN layers have a lower lattice mismatch, which not only improves subsequent crystal quality but also mitigates the effects of piezoelectric polarization, reducing carrier separation, thereby increasing the probability of radiative recombination and boosting luminous efficiency. The second stepped recombination layer 62 not only blocks electron overflow, but the Mg doping and MgN material also enhance hole injection efficiency. Mg doping also reduces the height of the potential barrier peak in the valence band that impedes hole injection due to piezoelectric polarization, further improving hole injection efficiency. A two-dimensional electron gas is formed between the third InAlN layer 631, the third AlN layer 632 and the third InGaN layer 633 in the third stepped composite layer 63. The two-dimensional electron gas has a repulsive force on the electrons in the active layer, which can effectively confine the electrons in the active layer, thereby improving the effective recombination efficiency between electrons and holes, and thus improving the luminous efficiency.

[0050] In one embodiment, the thicknesses of the first InAlN layer 611 and the first InGaN layer 612 are 1 nm to 5 nm, respectively; the thicknesses of the second Mg-doped InAlN layer 621, the second AlN layer 622, and the second MgN layer 623 are 1 nm to 5 nm, respectively; and the thicknesses of the third InAlN layer 631, the third AlN layer 632, and the third InGaN layer 633 are 3 nm to 10 nm, respectively. By optimizing the thickness of each layer, electron overflow can be effectively blocked, leakage current density can be controlled to an extremely low level, and hole injection efficiency can be improved, so that the wave functions of electrons and holes are highly overlapped in the multi-quantum well light-emitting layer 5, thereby significantly increasing the probability of radiative recombination.

[0051] Specifically, the thicknesses of the first InAlN layer 611 and the first InGaN layer 612 are illustratively 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm, respectively, but are not limited thereto. The thicknesses of the second Mg-doped InAlN layer 621, the second AlN layer 622, and the second MgN layer 623 are illustratively 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm, respectively, but are not limited thereto. The thicknesses of the third InAlN layer 631, the third AlN layer 632, and the third InGaN layer 633 are illustratively 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm, respectively, but are not limited thereto.

[0052] In one embodiment, the number of periods of periodic alternating stacking of the first stepped composite layer 61 is 1 to 3; the number of periods of periodic alternating stacking of the second stepped composite layer 62 is 3 to 5; and the number of periods of periodic alternating stacking of the third stepped composite layer 63 is 3 to 5.

[0053] The first stepped composite layer 61 adopts a superlattice structure material formed by alternatingly stacking a first InAlN layer 611 and a first InGaN layer 612, with the number of alternating stacking periods being 1 to 3; the second stepped composite layer 62 adopts a superlattice structure material formed by alternatingly stacking a second Mg-doped InAlN layer 621, a second AlN layer 622, and a second MgN layer 623, with the number of alternating stacking periods being 3 to 5; the third stepped composite layer 63 adopts a superlattice structure material formed by alternatingly stacking a third InAlN layer 631, a third AlN layer 632, and a third InGaN layer 633, with the number of alternating stacking periods being 3 to 5, which can effectively improve the hole injection efficiency, thereby improving the luminous efficiency of the LED chip at low operating current density.

[0054] Specifically, the number of periods of the periodic alternating stacking of the first stepped composite layer 61 is exemplarily 1, 2 or 3;

[0055] The number of periods of the periodic alternating stacking of the second stepped composite layer 62 is exemplarily 3, 4 or 5;

[0056] The number of periods of the periodic alternating stacking of the third stepped composite layer 63 is exemplarily 3, 4 or 5.

[0057] In one embodiment, the Mg doping concentration in the second Mg-doped InAlN layer 621 is 5×10 18 atoms / cm 3 ~5×10 19 atoms / cm 3, and the Mg doping concentration decreases layer by layer along the growth direction of the second stepped composite layer 62. Within this Mg doping concentration range, the local electric field caused by the acceptor impurity can partially offset the piezoelectric polarization field, reduce the height of the barrier peak, and make it easier for holes to be injected into the multi-quantum well light-emitting layer 5, thereby improving the hole injection efficiency. However, the Mg doping concentration in the second Mg-doped InAlN layer 621 should not exceed 5×10 19 atoms / cm 3 Excessive doping can introduce lattice stress, increase dislocation density, and damage the quality of the layer interface. Furthermore, by further optimizing the Mg doping concentration of each second Mg-doped InAlN layer 621 in the second stepped composite layer 62, the Mg doping concentration is reduced layer by layer during the deposition process, further improving the hole injection efficiency and thus the luminous efficiency of the Micro LED chip at low operating current density.

[0058] In one embodiment, along the growth direction of the second stepped composite layer 62, the Mg doping concentration of the second Mg-doped InAlN layer 621 in the nth period is C 1, the Mg doping concentration of the second Mg-doped InAlN layer 621 in the n+1th period is C 2, where n is 1, 2, 3, or 4;

[0059] C 1 and C 2 satisfies the following formula: C 2=(0.68~0.85) C 1. It is conducive to further improving the luminous efficiency of Micro LED chips at low operating current density.

[0060] In one embodiment, the Al content in the first InAlN layer 611, the second Mg-doped InAlN layer 621, and the third InAlN layer 631 is 0.1-0.8, respectively. This allows the first InAlN layer 611, the second Mg-doped InAlN layer 621, and the third InAlN layer 631 to have a relatively high bandgap, effectively reducing electron mobility and the influence of piezoelectric polarization. This increases the overlap of electron and hole wave functions, thereby improving the luminous efficiency of the LED device.

[0061] Specifically, the proportions of Al components in the first InAlN layer 611 , the second Mg-doped InAlN layer 621 , and the third InAlN layer 631 are exemplarily 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8, respectively.

[0062] In one embodiment, the multi-quantum well light-emitting layer 5 includes InGaN quantum well layers and AlGaN quantum barrier layers that are periodically and alternately stacked in sequence, and the number of alternating stacking periods is 5 to 20; specifically, the number of alternating stacking periods is exemplarily 5, 10, 12, 15, 18, and 20, but is not limited thereto;

[0063] The InGaN quantum well layer has an In component ratio of 0.01 to 0.3 and a thickness of 2 nm to 5 nm. Specifically, the In component ratio of the InGaN quantum well layer is 0.01, 0.1, 0.16, 0.23, and 0.3, and the thickness is 2 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, and 5 nm, but is not limited thereto.

[0064] The AlGaN quantum barrier layer has an Al content of 0.01 to 0.1 and a thickness of 5 nm to 15 nm. Specifically, the Al content of the AlGaN quantum barrier layer is 0.01, 0.05, 0.08, or 0.1, and the thickness is 5 nm, 8 nm, 9.8 nm, 11 nm, 13 nm, or 15 nm, but is not limited thereto.

[0065] The multi-quantum well light-emitting layer 5 is the area where electrons and holes recombine. Reasonable structural design can significantly increase the degree of overlap of electron and hole wave functions, thereby improving the luminous efficiency of the LED device.

[0066] In one embodiment, the P-type GaN layer 7 is doped with Mg, and the Mg doping concentration is 1×10 19 atoms / cm 3 ~1×10 21 atoms / cm 3 The hole concentration generated within this range is high and the crystal quality is good. If the Mg doping concentration is too high, the crystal quality will be damaged. If the Mg doping concentration is too low, the hole concentration generated will be low, which will in turn affect the luminous efficiency of the LED chip. Specifically, the Mg doping concentration in the P-type GaN layer 7 is exemplarily 1×10 19 atoms / cm 3 , 5×10 19 atoms / cm 3 , 2×10 20 atoms / cm 3 , 5×10 20 atoms / cm 3 , 1×10 21 atoms / cm 3 , but not limited to this.

[0067] In one embodiment, the thickness of the P-type GaN layer 7 is 10 nm to 50 nm, exemplified by 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, and 50 nm, but not limited thereto.

[0068] Preferably, the high hole injection efficiency epitaxial structure further includes a substrate 1, on which a buffer layer 2, a U-GaN layer 3, an N-GaN layer 4, a multi-quantum well light-emitting layer 5, a P-GaN composite layer 6 and a P-type GaN layer 7 are sequentially stacked.

[0069] Accordingly, this embodiment also discloses a method for preparing an epitaxial structure with high hole injection efficiency, comprising the following steps:

[0070] (1) Growing a buffer layer 2 on a substrate 1; preferably, the substrate 1 can be a (0001) sapphire substrate, an AlN substrate, a Si(111) substrate, a SiC(0001) substrate, etc. Specifically, the substrate is a sapphire substrate, which has the advantages of mature preparation technology, low price, easy cleaning and processing, and good stability at high temperatures.

[0071] (2) growing a U-GaN layer 3 on the buffer layer 2;

[0072] (3) growing an N-GaN layer 4 on the U-GaN layer 3;

[0073] (4) growing a multi-quantum well light-emitting layer 5 on the N-GaN layer 4;

[0074] (5) growing a P-GaN composite layer 6 on the multi-quantum well light-emitting layer 5;

[0075] (6) growing a P-type GaN layer 7 on the P-GaN composite layer 6;

[0076] The P-GaN composite layer 6 includes a first stepped composite layer 61, a second stepped composite layer 62 and a third stepped composite layer 63 stacked in sequence;

[0077] The first stepped composite layer 61 includes a first InAlN layer 611 and a first InGaN layer 612 that are periodically and alternately stacked in sequence; the second stepped composite layer 62 includes a second Mg-doped InAlN layer 621, a second AlN layer 622, and a second MgN layer 623 that are periodically and alternately stacked in sequence; the third stepped composite layer 63 includes a third InAlN layer 631, a third AlN layer 632, and a third InGaN layer 633 that are periodically and alternately stacked in sequence.

[0078] In one embodiment, in step (5), the growth temperature of the P-GaN composite layer 6 is 600°C to 1000°C, and the growth pressure is 100 torr to 500 torr. Specifically, the growth temperature of the P-GaN composite layer 6 is exemplarily 600°C, 680°C, 700°C, 800°C, 880°C, 950°C, and 1000°C, but is not limited thereto. The growth pressure of the P-GaN composite layer 6 is exemplarily 100 torr, 120 torr, 150 torr, 180 torr, 200 torr, 250 torr, 300 torr, 350 torr, 380 torr, 400 torr, 420 torr, 480 torr, and 500 torr, but is not limited thereto.

[0079] In one embodiment, in step (1), the buffer layer 2 is an AlN buffer layer.

[0080] An AlN buffer layer is deposited in PVD. The thickness of the AlN buffer layer is 40-60 nm. The AlN buffer layer provides nucleation centers with the same orientation as the substrate 1, which is beneficial for providing a flat nucleation surface for the further growth of the subsequent epitaxial layer. The contact angle of its nucleation growth is reduced so that the island-like grown GaN grains can be connected into a surface within a smaller thickness, thereby transforming into two-dimensional epitaxial growth. This is beneficial for improving the crystal quality of the subsequently deposited U-GaN layer 3 and N-GaN layer 4, reducing the dislocation density, and improving the radiation recombination efficiency of the multi-quantum well light-emitting layer 5.

[0081] Preferably, in steps (2) to (6), MOCVD (Metal-organic Chemical Vapor Deposition, MOCVD for short) equipment is used, one of high-purity H (hydrogen), high-purity N2 (nitrogen), and a mixed gas of high-purity H2 and high-purity N2 is used as a carrier gas, high-purity NH3 is used as an N source, trimethylgallium (TMGa) and triethylgallium (TEGa) are used as gallium sources, trimethylaluminum (TMAl) is used as an aluminum source, silane (SiH4) is used as an N-type dopant, and bis(cyclopentadienyl)magnesium (CP2Mg) is used as a P-type dopant for epitaxial growth.

[0082] In one embodiment, in step (2), a U-GaN layer 3 (i.e., an unintentionally doped GaN layer) is deposited on the buffer layer 2 at a growth temperature of 1100°C to 1150°C, a growth pressure of 100 torr to 500 torr, and a thickness of 1 to 3 μm. The higher the growth temperature and lower the pressure, the better the quality of the GaN crystals produced.

[0083] Specifically, the growth temperature of the U-GaN layer 3 is exemplarily, but not limited to, 1100° C., 1120° C., 1130° C., 1140° C., or 1150° C. The growth pressure of the U-GaN layer 3 is exemplarily, but not limited to, 100 torr, 120 torr, 150 torr, 180 torr, 200 torr, 300 torr, 400 torr, or 500 torr. The thickness of the U-GaN layer 3 is exemplarily, but not limited to, 1 μm, 2 μm, or 3 μm.

[0084] In one embodiment, in step (3), an N-GaN layer 4 is grown on the U-GaN layer 3. Preferably, the N-GaN layer is an N-type GaN layer.

[0085] Preferably, the N-GaN layer 4 is doped with Si, and the Si doping concentration is 1×10 19 atoms / cm 3 ~5×10 20 atoms / cm 3 , with a thickness of 1μm to 5μm, a growth temperature of 1000℃ to 1300℃, and a growth pressure of 100torr to 500tor. First, the N-GaN layer 4 can provide sufficient electrons for recombination with holes for LED light emission; second, the resistivity of the N-GaN layer 4 is higher than that of the transparent electrode on the P-type GaN layer 7. Within a certain range of Si doping concentration, the resistivity of the N-GaN layer 4 can be effectively reduced; finally, within a certain range of thickness of the N-GaN layer 4, it can effectively release stress and improve the luminous efficiency of the light-emitting diode.

[0086] Specifically, the Si doping concentration in the N-GaN layer 4 is exemplarily 1×10 19 atoms / cm 3 , 2.5×10 19 atoms / cm 3 , 5×10 19 atoms / cm 3 , 1×10 20 atoms / cm 3 , 2.5×10 20 atoms / cm 3 , 5×10 20 atoms / cm 3, but not limited thereto. The growth temperature of the N-GaN layer 4 is exemplarily 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, or 1300°C, but not limited thereto. The growth pressure of the N-GaN layer 4 is exemplarily 100 Torr, 200 Torr, 300 Torr, 400 Torr, or 500 Torr, but not limited thereto. The thickness of the N-GaN layer 4 is exemplarily 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, but not limited thereto.

[0087] In one embodiment, the multi-quantum well light-emitting layer 5 in step (4) includes InGaN quantum well layers and AlGaN quantum barrier layers that are periodically and alternately stacked in sequence, wherein the growth temperature of the InGaN quantum well layer is 760°C~810°C, and the growth pressure is 50torr~300torr; the growth temperature of the AlGaN quantum barrier layer is 800°C~900°C, and the growth pressure is 50torr~300torr.

[0088] Specifically, the growth temperature of the InGaN quantum well layer is exemplarily 760°C, 765°C, 780°C, 790°C, 800°C, and 810°C, and the growth pressure is exemplarily 50 Torr, 100 Torr, 150 Torr, 200 Torr, 250 Torr, and 300 Torr, but is not limited thereto. The growth temperature of the AlGaN quantum barrier layer is exemplarily 800°C, 820°C, 855°C, 880°C, and 900°C, and the growth pressure is exemplarily 50 Torr, 100 Torr, 150 Torr, 200 Torr, 250 Torr, and 300 Torr, but is not limited thereto.

[0089] In one embodiment, in step (6), the growth temperature of the P-type GaN layer 7 is 900° C. to 1050° C., and the growth pressure is 100 torr to 600 torr. A higher growth temperature of the P-type GaN layer 7 is conducive to obtaining an epitaxial structure with a smooth surface. Specifically, the growth temperature of the P-type GaN layer 7 is exemplarily 900° C., 950° C., 985° C., 1000° C., and 1050° C., and the growth pressure is exemplarily 100 torr, 200 torr, 300 torr, 400 torr, 500 torr, and 600 torr, but is not limited thereto.

[0090] The technical solution of the present invention is further described below through examples and comparative examples.

[0091] Example 1

[0092] This embodiment provides an epitaxial structure with high hole injection efficiency, comprising a substrate 1, and a buffer layer 2, a U-GaN layer 3, an N-GaN layer 4, a multi-quantum well light-emitting layer 5, a P-GaN composite layer 6, and a P-type GaN layer 7 stacked sequentially on the substrate 1;

[0093] The P-GaN composite layer 6 includes a first stepped composite layer 61, a second stepped composite layer 62 and a third stepped composite layer 63 stacked in sequence;

[0094] The first stepped composite layer 61 includes a first InAlN layer 611 and a first InGaN layer 612 that are periodically and alternately stacked, with one period. The thickness of the first InAlN layer 611 and the first InGaN layer 612 are both 3 nm. The proportion of Al in the first InAlN layer 611 is 0.2.

[0095] The second stepped composite layer 62 includes a second Mg-doped InAlN layer 621, a second AlN layer 622, and a second MgN layer 623 that are periodically and alternately stacked in sequence, with a period number of 3. The thicknesses of the second Mg-doped InAlN layer 621, the second AlN layer 622, and the second MgN layer 623 are 2 nm respectively. The proportion of Al component in the second Mg-doped InAlN layer 621 is 0.1. Along the growth direction of the second stepped composite layer 62, the Mg doping concentration in the second Mg-doped InAlN layer 621 in the first period is 2×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the second period is 1×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the third period is 5×10 18 atoms / cm 3 ;

[0096] The third stepped composite layer 63 includes a third InAlN layer 631, a third AlN layer 632 and a third InGaN layer 633 that are periodically and alternately stacked in sequence, with the number of periods being 3; the thicknesses of the third InAlN layer 631, the third AlN layer 632 and the third InGaN layer 633 are 5 nm, 4 nm and 5 nm respectively; the proportion of Al component in the third InAlN layer 631 is 0.1.

[0097] The multi-quantum well light-emitting layer 5 includes InGaN quantum well layers and AlGaN quantum barrier layers that are periodically stacked alternately, with the number of alternating stacking periods being 10. The InGaN quantum well layer has an In component ratio of 0.23 and a thickness of 3.5 nm. The AlGaN quantum barrier layer has an Al component ratio of 0.05 and a thickness of 9 nm. The P-type GaN layer 7 is doped with Mg, and the Mg doping concentration is 2×10 20 atoms / cm 3 ; The thickness of the P-type GaN layer 7 is 15nm.

[0098] The method for preparing an epitaxial structure with high hole injection efficiency in this embodiment includes the following steps:

[0099] (1) growing a buffer layer 2 on a substrate 1;

[0100] (2) growing a U-GaN layer 3 on the buffer layer 2;

[0101] (3) growing an N-GaN layer 4 on the U-GaN layer 3;

[0102] (4) growing a multi-quantum well light-emitting layer 5 on the N-GaN layer 4;

[0103] (5) growing a P-GaN composite layer 6 on the multi-quantum well light-emitting layer 5; wherein the growth temperature of the P-GaN composite layer 6 is 880° C. and the growth pressure is 150 Torr;

[0104] (6) A P-type GaN layer 7 is grown on the P-GaN composite layer 6.

[0105] Example 2

[0106] This embodiment provides an epitaxial structure with high hole injection efficiency, which is basically the same as the embodiment 1, except that: in the embodiment 2, the number of periods of the periodic alternating stacking of the second stepped composite layer 62 is 5; and along the growth direction of the second stepped composite layer 62, the Mg doping concentration in the second Mg-doped InAlN layer 621 of the first period is 2.5×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the second period is 1.875×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the third period is 1.4×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the fourth period is 1.05×10 19 atoms / cm 3The Mg doping concentration in the second Mg-doped InAlN layer 621 of the fifth period is 7.9×10 18 atoms / cm 3 ; That is, the Mg doping concentration of the second Mg-doped InAlN layer 621 in the n+1th period C 2 is the Mg doping concentration of the second Mg-doped InAlN layer 621 in the nth period C 0.75 times of 1, that is C 2=0.75 C 1.

[0107] Example 3

[0108] This embodiment provides an epitaxial structure with high hole injection efficiency, which is basically the same as Example 2, except that: in Example 3, the number of periods of the first stepped composite layer 61 is 3, the proportion of Al component in the first InAlN layer 611 is 0.7, the proportion of Al component in the second Mg-doped InAlN layer 621 is 0.6, and the proportion of Al component in the third InAlN layer 631 is 0.6.

[0109] Example 4

[0110] This embodiment provides an epitaxial structure with high hole injection efficiency, which is basically the same as the embodiment 1, except that: in the second stepped composite layer 62 of the embodiment 4, the Mg doping concentration in the second Mg-doped InAlN layer 621 of each period is 8×10 18 atoms / cm 3 .

[0111] Example 5

[0112] This embodiment provides an epitaxial structure with high hole injection efficiency, which is basically the same as the embodiment 2, except that: in the embodiment 5, the thickness of the second Mg-doped InAlN layer 621 and the second MgN layer 623 are both 5 nm; and along the growth direction of the second stepped composite layer 62, the Mg doping concentration in the second Mg-doped InAlN layer 621 of the first period is 3.8×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the second period is 3.04×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the third period is 2.432×10 19 atoms / cm 3 The Mg doping concentration in the second Mg-doped InAlN layer 621 of the fourth period is 1.95×10 19 atoms / cm 3The Mg doping concentration in the second Mg-doped InAlN layer 621 of the fifth period is 1.56×10 19 atoms / cm 3 ; That is, the Mg doping concentration of the second Mg-doped InAlN layer 621 in the n+1th period C 2 is the Mg doping concentration of the second Mg-doped InAlN layer 621 in the nth period C 0.8 times of 1, that is C 2=0.8 C 1.

[0113] Comparative Example 1

[0114] This comparative example provides a traditional epitaxial structure, including a substrate, and a buffer layer, a U-GaN layer, an N-GaN layer, a multi-quantum well light-emitting layer, an electron blocking layer (p-AlGaN layer) and a P-type GaN layer stacked in sequence on the substrate.

[0115] Comparative Example 2

[0116] This comparative example provides an epitaxial structure with high hole injection efficiency, which is basically the same as Example 1, except that the P-GaN composite layer in Comparative Example 2 is composed of a first stepped composite layer and a second stepped composite layer stacked in sequence, that is, the third stepped composite layer in Example 1 is removed in this comparative example.

[0117] Comparative Example 3

[0118] This comparative example provides an epitaxial structure with high hole injection efficiency, which is basically the same as Example 1, except that the P-GaN composite layer in Comparative Example 3 is composed of a first stepped composite layer and a third stepped composite layer stacked in sequence, that is, the second stepped composite layer in Example 1 is removed in this comparative example.

[0119] Performance testing:

[0120] The epitaxial structures obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were fabricated into 3 mil*5 mil Micro LED chips using the same chip process conditions. The luminous efficiency was tested at an operating current of 2 mA. Based on Comparative Example 1, the luminous efficiency improvement rate of each Example and Comparative Example was calculated:

[0121] Light efficiency improvement rate = (improved light efficiency - original light efficiency) / original light efficiency × 100%;

[0122] In the above calculation formula, the original light effect is the light effect of Comparative Example 1.

[0123] Specifically, the performance test results are shown in Table 1 below.

[0124] Table 1 Performance test results

[0125]

[0126] It can be seen from the above experimental data that Examples 1 to 5 improve the epitaxial structure by setting a P-GaN composite layer between the multi-quantum well light-emitting layer and the P-type GaN layer. Through the coordinated effect of each layer in the P-GaN composite layer, the hole injection efficiency can be effectively improved and the effective recombination between electrons and holes can be promoted, thereby improving the luminous efficiency of the Micro LED chip at low operating current density.

[0127] The above disclosure is only a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A high hole injection efficiency epitaxial structure, characterized in that: It includes a buffer layer, a U-GaN layer, an N-GaN layer, a multi-quantum well light-emitting layer, a P-GaN composite layer and a P-type GaN layer stacked in sequence; The P-GaN composite layer includes a first stepped composite layer, a second stepped composite layer and a third stepped composite layer stacked in sequence; The first stepped composite layer includes a first InAlN layer and a first InGaN layer that are periodically and alternately stacked in sequence; The second stepped composite layer includes a second Mg-doped InAlN layer, a second AlN layer, and a second MgN layer that are periodically and alternately stacked in sequence; The third stepped composite layer includes a third InAlN layer, a third AlN layer and a third InGaN layer which are periodically and alternately stacked in sequence; The Mg doping concentration in the second Mg-doped InAlN layer is 5×10 18 atoms / cm 3 ~5×10 19 atoms / cm 3 , and along the growth direction of the second stepped composite layer, the Mg doping concentration decreases layer by layer.

2. The high hole injection efficiency epitaxial structure according to claim 1, characterized in that: The thicknesses of the first InAlN layer and the first InGaN layer are 1 nm to 5 nm respectively; The thicknesses of the second Mg-doped InAlN layer, the second AlN layer and the second MgN layer are 1 nm to 5 nm respectively; The thicknesses of the third InAlN layer, the third AlN layer, and the third InGaN layer are 3 nm to 10 nm, respectively.

3. The high hole injection efficiency epitaxial structure according to claim 2, characterized in that: The number of periods of the periodic alternating stacking of the first stepped composite layer is 1 to 3; The number of periods of the periodic alternating stacking of the second stepped composite layer is 3 to 5; The number of periods of the periodic alternating stacking of the third stepped composite layer is 3 to 5.

4. The high hole injection efficiency epitaxial structure according to claim 1, wherein: Along the growth direction of the second stepped composite layer, the Mg doping concentration of the second Mg-doped InAlN layer in the nth period is C 1. The Mg doping concentration of the second Mg-doped InAlN layer in the n+1th period is C 2, where n is 1, 2, 3, or 4; C 1 and C 2 satisfies the following formula: C 2=(0.68~0.85) C 1.

5. The high hole injection efficiency epitaxial structure according to claim 1, wherein: The proportions of Al components in the first InAlN layer, the second Mg-doped InAlN layer, and the third InAlN layer are 0.1-0.8, respectively.

6. The high hole injection efficiency epitaxial structure according to claim 1, characterized in that: The multi-quantum well light-emitting layer includes InGaN quantum well layers and AlGaN quantum barrier layers that are periodically and alternately stacked in sequence, and the number of cycles of the alternating stacking is 5 to 20; The InGaN quantum well layer has an In component ratio of 0.01 to 0.3 and a thickness of 2 nm to 5 nm. The AlGaN quantum barrier layer has an Al component ratio of 0.01-0.1 and a thickness of 5 nm-15 nm.

7. The high hole injection efficiency epitaxial structure according to claim 1, characterized in that: The P-type GaN layer is doped with Mg, and the Mg doping concentration is 1×10 19 atoms / cm 3 ~1×10 21 atoms / cm 3 ; The thickness of the P-type GaN layer is 10 nm to 50 nm.

8. A method for preparing an epitaxial structure with high hole injection efficiency, characterized in that: The method for preparing the epitaxial structure with high hole injection efficiency according to any one of claims 1 to 7 comprises the following steps: (1) Growing a buffer layer on the substrate; (2) Growing a U-GaN layer on the buffer layer; (3) Growing an N-GaN layer on the U-GaN layer; (4) Growing a multi-quantum well light-emitting layer on the N-GaN layer; (5) Growing a P-GaN composite layer on the multi-quantum well light-emitting layer; (6) Growing a P-type GaN layer on the P-GaN composite layer; The P-GaN composite layer includes a first stepped composite layer, a second stepped composite layer and a third stepped composite layer stacked in sequence; The first stepped composite layer includes a first InAlN layer and a first InGaN layer that are periodically and alternately stacked in sequence; the second stepped composite layer includes a second Mg-doped InAlN layer, a second AlN layer, and a second MgN layer that are periodically and alternately stacked in sequence; and the third stepped composite layer includes a third InAlN layer, a third AlN layer, and a third InGaN layer that are periodically and alternately stacked in sequence.

9. The method for preparing an epitaxial structure with high hole injection efficiency according to claim 8, characterized in that: In step (5), the growth temperature of the P-GaN composite layer is 600° C. to 1000° C., and the growth pressure is 100 torr to 500 torr.

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