Deep ultraviolet LED epitaxial wafer and epitaxial growth method thereof

Abstract

The invention provides a deep ultraviolet LED epitaxial wafer and an epitaxial growth method thereof.The deep ultraviolet LED epitaxial wafer comprises a substrate, a buffer layer, an intrinsic layer, an electron injection layer, a current expansion layer, a quantum well active layer, an electron blocking layer, a hole injection layer and an ohmic contact layer which are sequentially arranged in a stacked mode in the growth direction, an impurity absorption layer is further arranged between the quantum well active layer and the electron blocking layer, the impurity absorption layer is made of AlGaN, and at least one part of the impurity absorption layer is unintentionally doped; the N-type impurity concentration gradient is formed between the electron injection layer and the impurity absorption layer, and meanwhile, the P-type impurity concentration gradient is formed between the hole injection layer and the impurity absorption layer, so that the N-type impurities and the P-type impurities are promoted to diffuse into the impurity absorption layer, and the radiation recombination efficiency of the quantum well active layer is further improved; and finally, the luminous efficiency of the deep ultraviolet LED epitaxial wafer is improved.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronics, and in particular to a deep ultraviolet LED epitaxial wafer and an epitaxial growth method thereof. Background Art

[0002] In deep ultraviolet LED epitaxial wafers, SiH4 is usually used as an N-type dopant and bismuth magnesium is used as a P-type dopant. However, in the actual growth process, the Si element in the N-type doping layer and the quantum well active region tends to diffuse into the electron blocking layer, and the Mg element in the electron blocking layer or the p-type doping layer also diffuses into the quantum well active region. The impurities formed by this mutual diffusion will capture electron-hole pairs, thereby reducing the radiation recombination efficiency and further reducing the luminous efficiency of the deep ultraviolet LED epitaxial wafer.

[0003] Therefore, it is necessary to propose a new deep ultraviolet LED epitaxial wafer and its epitaxial growth method to solve the above-mentioned problems existing in the prior art. Summary of the invention

[0004] The object of the present invention is to provide a deep ultraviolet LED epitaxial wafer and an epitaxial growth method thereof, so as to improve the technical problem of low luminous efficiency of the deep ultraviolet LED epitaxial wafer in the prior art.

[0005] In order to solve the above technical problems, the present invention provides a deep ultraviolet LED epitaxial wafer, comprising a substrate, a buffer layer, an intrinsic layer, an electron injection layer, a current expansion layer, a quantum well active layer, an electron blocking layer, a hole injection layer and an ohmic contact layer which are sequentially stacked along a growth direction; An impurity absorption layer is arranged between the quantum well active layer and the electron blocking layer; the material of the impurity absorption layer is AlGaN, and at least a part of the impurity absorption layer is unintentionally doped.

[0006] Preferably, the impurity absorption layer is a single-layer AlGaN structure, the mass content of the Al component in the impurity absorption layer is 20% to 90%, and the thickness of the impurity absorption layer is 1 nm to 500 nm.

[0007] Preferably, the Al component content of the impurity absorption layer increases linearly along the growth direction; the Al component mass content at the contact interface between the impurity absorption layer and the quantum well active layer is 20% to 70%, and the Al component mass content at the contact interface between the impurity absorption layer and the electron blocking layer is 40% to 90%.

[0008] Preferably, the impurity absorption layer includes a plurality of periodic structures, each of which includes a first sublayer and a second sublayer stacked in sequence along the growth direction, and the material of the first sublayer is Al a Ga 1-a N, the material of the second sublayer is Al b Ga 1-bN, a is the mass content of Al component in the first sub-layer, b is the mass content of Al component in the second sub-layer, and a and b satisfy the following relationship: 20%≤b≤a≤90%; The thickness of the first sublayer is 1 nm to 20 nm, the thickness of the second sublayer is 2 nm to 20 nm, and the number of periods of the impurity absorption layer is 2 to 50.

[0009] Preferably, the impurity absorption layer is a whole layer that is not intentionally doped.

[0010] Preferably, the impurity absorption layer includes an N-type doped portion close to the quantum well active layer, a P-type doped portion close to the electron blocking layer, and an unintentionally doped portion between the N-type doped portion and the P-type doped portion; The doping concentration of the N-type doped part is 1E16cm -3 ~5E18cm -3 The doping concentration of the P-type doping part is 1E16cm -3 ~5E18cm -3 .

[0011] Preferably, the quantum well active layer comprises at least one potential well layer and at least two potential barrier layers which are alternately arranged, each potential well layer is inserted between two adjacent potential barrier layers, and the quantum well active layer comprises n potential well layers, where n≥1 and n is a positive integer; Among them, the P-type impurity concentration in the (n-1) potential well layers arranged along the growth direction of the quantum well active layer is lower than 5E17cm -3 ; The P-type impurity concentration in the nth potential well layer arranged along the growth direction of the quantum well active layer is lower than 1E18cm -3 .

[0012] Preferably, the N-type impurity concentration in the electron blocking layer is lower than 8E17cm -3 ; The N-type impurity concentration in the hole injection layer and the ohmic contact layer is less than 5E17cm -3 .

[0013] Accordingly, the present invention also provides an epitaxial growth method of the above deep ultraviolet LED epitaxial wafer, the epitaxial growth method comprising: S10, epitaxially growing a buffer layer, an intrinsic layer, an electron injection layer, a current spreading layer and a quantum well active layer on the substrate in sequence; S20, epitaxially growing an impurity absorption layer on the quantum well active layer, wherein the material of the impurity absorption layer is AlGaN, and at least a portion of the impurity absorption layer is unintentionally doped; S30, epitaxially growing an electron blocking layer, a hole injection layer and an ohmic contact layer in sequence on the impurity absorption layer.

[0014] Preferably, before performing step S20, the process also includes: introducing H2 into the growth furnace to anneal the quantum well active layer, the annealing temperature is 500°C~900°C, and the annealing time is 1min~60min; before performing step S30, the process also includes: introducing N2 into the growth furnace to anneal the impurity absorption layer, the annealing temperature is 500°C~900°C, and the annealing time is 1min~60min.

[0015] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a deep ultraviolet LED epitaxial wafer and an epitaxial growth method thereof, wherein the deep ultraviolet LED epitaxial wafer comprises a substrate, a buffer layer, an intrinsic layer, an electron injection layer, a current expansion layer, a quantum well active layer, an electron blocking layer, a hole injection layer and an ohmic contact layer which are sequentially stacked along a growth direction, wherein an impurity absorption layer is further arranged between the quantum well active layer and the electron blocking layer, the material of the impurity absorption layer is AlGaN, and at least a portion of the impurity absorption layer is unintentionally doped; the present invention achieves a deep ultraviolet LED epitaxial wafer and an epitaxial growth method thereof by stacking the substrate, a buffer layer, an intrinsic layer, an electron injection layer, a current expansion layer, a quantum well active layer, an electron blocking layer, a hole injection layer and an ohmic contact layer in sequence along a growth direction, wherein an impurity absorption layer is further arranged between the quantum well active layer and the electron blocking layer, the material of the impurity absorption layer is AlGaN, and at least a portion of the impurity absorption layer is unintentionally doped; An impurity absorption layer is arranged between the barrier layers, and at least a portion of the impurity absorption layer is unintentionally doped to form an N-type impurity concentration gradient between the electron injection layer and the impurity absorption layer, and at the same time form a P-type impurity concentration gradient between the hole injection layer and the impurity absorption layer. The above-mentioned N-type impurity concentration gradient and P-type impurity concentration gradient will generate a diffusion driving force, thereby promoting the diffusion of N-type impurities and P-type impurities into the impurity absorption layer, and then the impurity absorption layer can absorb N-type impurities and P-type impurities, further improve the radiation recombination efficiency of the quantum well active layer, and finally improve the luminescence efficiency of the deep ultraviolet LED epitaxial wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the cross-sectional structure of a deep ultraviolet LED epitaxial wafer provided in an embodiment of the present invention; Figure 2 A process flow chart of the epitaxial growth method of a deep ultraviolet LED epitaxial wafer provided in an embodiment of the present invention; Figure 3 A distribution diagram of element contents in each epitaxial layer near the quantum well active layer and the electron blocking layer in the deep ultraviolet LED epitaxial wafer provided in Example 1 of the present invention; Figure 4 The element content distribution diagram in each epitaxial layer near the quantum well active layer and the electron blocking layer in the deep ultraviolet LED epitaxial wafer provided for comparative example.

[0017] In the figure: 100 - deep ultraviolet LED epitaxial wafer; 101 - substrate; 102 - buffer layer; 103 - intrinsic layer; 104 - electron injection layer; 105 - current spreading layer; 106 - quantum well active layer; 107 - impurity absorption layer; 108 - electron blocking layer; 109 - hole injection layer; 110 - ohmic contact layer; 111 - N-type electrode; 112 - P-type electrode. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In view of the technical problem that the deep ultraviolet LED epitaxial wafer 100 in the prior art has low luminous efficiency, the present invention proposes a special deep ultraviolet LED epitaxial wafer 100. Through the epitaxial growth of the impurity absorption layer 107, the P-type impurity concentration in the quantum well active layer 106 and the epitaxial layer before it will be significantly reduced, and the N-type impurity concentration in the electron blocking layer 108 and the epitaxial layer after it will also be significantly reduced, thereby ultimately improving the luminous efficiency of the deep ultraviolet LED epitaxial wafer 100.

[0020] See also Figure 1 , Figure 1 A schematic diagram of the cross-sectional structure of a deep ultraviolet LED epitaxial wafer 100 provided in an embodiment of the present invention; wherein the present invention first provides a deep ultraviolet LED epitaxial wafer 100, wherein the deep ultraviolet LED epitaxial wafer 100 comprises a substrate 101, a buffer layer 102, an intrinsic layer 103, an electron injection layer 104, a current spreading layer 105, a quantum well active layer 106, an electron blocking layer 108, a hole injection layer 109 and an ohmic contact layer 110 which are sequentially stacked along a growth direction; An impurity absorption layer 107 is further disposed between the quantum well active layer 106 and the electron blocking layer 108 . The material of the impurity absorption layer 107 is AlGaN, and at least a portion of the impurity absorption layer 107 is unintentionally doped.

[0021] In the embodiment of the present invention, the substrate 101 is made of sapphire material. Sapphire material has many advantages: first, the production technology of sapphire material is mature and the device quality is good; second, sapphire has good stability and can be used in high-temperature growth processes; finally, sapphire has high mechanical strength and is easy to handle and clean. Therefore, most processes generally use sapphire as the substrate 101.

[0022] In the embodiment of the present invention, the material of the buffer layer 102 is AlN, the growth temperature thereof is in the range of 400° C. to 800° C., and the thickness thereof is in the range of 10 nm to 50 nm.

[0023] In the embodiment of the present invention, the material of the intrinsic layer 103 is AlN, the growth temperature thereof is in the range of 1200° C. to 1400° C., and the thickness thereof is in the range of 500 nm to 4000 nm.

[0024] In an embodiment of the present invention, the material of the electron injection layer 104 is Si-doped AlGaN material, and the dopant is SiH4; wherein the mass content of the Al component of the electron injection layer 104 is between 20% and 90%, the thickness of the electron injection layer 104 is between 500nm and 4000nm, and the growth temperature of the electron injection layer 104103 is between 800°C and 1200°C.

[0025] In the embodiment of the present invention, the current spreading layer 105 is disposed on the electron injection layer 104, and the growth temperature of the current spreading layer 105 ranges from 700°C to 1100°C; specifically, the material of the current spreading layer 105 is AlGaN, the mass content of the Al component of the current spreading layer 105 is between 20% and 90%, and the thickness of the current spreading layer 105 ranges from 10nm to 300nm. The provision of the current spreading layer 105 can enhance the lateral expansion of the current inside the deep ultraviolet LED epitaxial wafer 100, thereby greatly improving the light extraction efficiency of the deep ultraviolet LED epitaxial wafer 100.

[0026] In the embodiment of the present invention, the quantum well active layer 106 is disposed on the current spreading layer 105, and the growth temperature of the quantum well active layer 106 is in the range of 700° C. to 1100° C. Specifically, the quantum well active layer 106 includes at least one potential well layer and at least two potential barrier layers that are alternately disposed, and each potential well layer is inserted between two adjacent potential barrier layers; wherein the potential well layer and the potential barrier layer both include AlGaN material, and the total content of aluminum components in each potential well layer is lower than the total content of aluminum components in each potential barrier layer, so as to ensure that the carriers in the quantum well active layer 106 are confined in the potential well layer.

[0027] Furthermore, the material of the potential well layer is Al x1 Ga y1 N, where 0<x1<80%, and x1+y1=1; the material of the barrier layer is Al x2 Ga y2 N, where 20%<x2<100%, and x2+y2=1.

[0028] Furthermore, the thickness of the potential well layer ranges from 0.1 nm to 5 nm, and the thickness of the barrier layer ranges from 5 nm to 30 nm; the period number of the quantum well active layer 106 is greater than or equal to 1 and less than or equal to 10, and the period number is a positive integer.

[0029] In an embodiment of the present invention, an impurity absorption layer 107 is disposed on the quantum well active layer 106, the material of the impurity absorption layer 107 is AlGaN, and at least a portion of the impurity absorption layer 107 is unintentionally doped; wherein, since at least a portion of the impurity absorption layer 107 is unintentionally doped, an N-type impurity concentration gradient is formed between the electron injection layer 104 and the impurity absorption layer 107, and a P-type impurity concentration gradient is formed between the hole injection layer 109 and the impurity absorption layer 107. The above-mentioned N-type impurity concentration gradient and P-type impurity concentration gradient will generate a diffusion driving force, thereby promoting N-type impurities and P-type impurities to diffuse into the impurity absorption layer 107, and then the impurity absorption layer 107 can absorb N-type impurities and P-type impurities, further improve the radiation recombination efficiency of the quantum well active layer 106, and finally improve the luminous efficiency of the deep ultraviolet LED epitaxial wafer 100.

[0030] In the first embodiment, the impurity absorption layer 107 is a single-layer AlGaN structure, the Al component mass content of the impurity absorption layer 107 is 20% to 90%, and the thickness of the impurity absorption layer 107 is 1 nm to 500 nm.

[0031] Specifically, the Al component content of the impurity absorption layer 107 increases linearly along the growth direction; the Al component mass content at the contact interface between the impurity absorption layer 107 and the quantum well active layer 106 is 20% to 70%, and the Al component mass content at the contact interface between the impurity absorption layer 107 and the electron blocking layer 108 is 40% to 90%.

[0032] Furthermore, the linearly increasing Al component in the impurity absorption layer 107 can form a gradually changing energy band structure, which helps to improve the electron and hole confinement ability. From the low Al component in contact with the quantum well active layer 106 to the high Al component in contact with the electron blocking layer 108, the energy band gradually increases, forming an effective electron and hole barrier, reducing the leakage of carriers; the linearly increasing Al component can gradually transition the lattice constant, reduce the lattice mismatch between the quantum well active layer 106 and the electron blocking layer 108, which helps to reduce the interface stress and defect density, improve the crystal quality of the material and the reliability of the device; with the increase of the Al component, the impurity absorption layer 107 may also enhance its absorption capacity for impurities. The linearly increasing Al component can provide different degrees of impurity absorption at different locations, optimizing the distribution and removal effect of impurities.

[0033] Furthermore, the mass content of the Al component at the interface between the impurity absorption layer 107 and the quantum well active layer 106 is 20% to 70%. This lower range helps to reduce the impact on the active area and maintain the luminescence efficiency of the quantum well active layer 106. At the same time, it can also provide a certain impurity absorption ability to prevent impurities from diffusing into the quantum well active layer 106; the mass content of the Al component at the interface between the impurity absorption layer 107 and the electron blocking layer 108 is 40% - 90%. A higher range can better cooperate with the electron blocking layer 108, enhance the blocking effect on electrons, reduce electron leakage, and improve the performance of the device.

[0034] In the second embodiment, the impurity absorption layer 107 includes a plurality of periodic structures, each of which includes a first sublayer and a second sublayer stacked in sequence along the growth direction. The material of the first sublayer is Al a Ga 1-a N, the material of the second sublayer is Al b Ga 1-b N, a is the mass content of Al component in the first sub-layer, b is the mass content of Al component in the second sub-layer, and a and b satisfy the following relationship: 20%≤b≤a≤90%; The thickness of the first sub-layer is 1 nm to 20 nm, the thickness of the second sub-layer is 2 nm to 20 nm, and the number of periods of the impurity absorption layer 107 is 2 to 50.

[0035] Furthermore, multiple periodic structures can achieve more precise control of the performance of the impurity absorption layer 107. By adjusting the material parameters and thickness of the first sublayer and the second sublayer in each period, the band structure, impurity absorption capacity, lattice matching and other characteristics can be accurately controlled; the combination of sublayers with different Al components can absorb impurities in different energy ranges, improve the efficiency and range of impurity absorption, each period can play a certain role in impurity capture, and the superposition of multiple periods further enhances the impurity absorption effect. The periodic structure can be designed to have a specific band arrangement, forming a quantum well or superlattice structure, which helps to improve the confinement capacity of electrons and holes and improve the transport and recombination efficiency of carriers.

[0036] Furthermore, the relationship of 20%≤b≤a≤90% ensures that the Al composition of the second sublayer does not exceed that of the first sublayer, forming a gradually changing Al composition distribution. This distribution can reduce lattice mismatch and interface stress, while providing a transition from low Al composition to high Al composition, which is beneficial to the absorption of impurities and the confinement of carriers.

[0037] Preferably, the impurity absorption layer 107 of the first embodiment and / or the second embodiment is a whole layer that is not intentionally doped.

[0038] Preferably, the impurity absorption layer 107 of the first embodiment and / or the second embodiment is segmented doped but contains at least a portion of unintentional doping; wherein the impurity absorption layer 107 includes an N-type doping portion close to the quantum well active layer 106, a P-type doping portion close to the electron blocking layer 108, and an unintentional doping portion between the N-type doping portion and the P-type doping portion; The doping concentration of the N-type doped part is 1E16cm -3 ~5E18cm -3 The doping concentration of the P-type doping part is 1E16cm -3 ~5E18cm -3 The above doping concentration range is relatively wide and can be adjusted according to specific device requirements. A lower doping concentration can avoid the degradation of crystal quality and increase of defects caused by excessive impurity concentration. A higher doping concentration can provide more carriers and improve device performance, but it is also necessary to avoid problems caused by over-doping.

[0039] Furthermore, the "segmented doping" design of the impurity absorption layer 107 can realize the control and management of different types of carriers; by performing specific types of doping in different regions, the electrical properties of the impurity absorption layer 107 can be optimized, and its absorption capacity for impurities and compatibility with adjacent layers can be improved; the N-type doping part is arranged near the quantum well active layer 106, which can promote the injection of electrons from the impurity absorption layer 107 to the quantum well active layer 106, and improve the luminous efficiency of the deep ultraviolet LED epitaxial wafer 100; the P-type doping part is arranged near the electron blocking layer 108, which can cooperate with the electron blocking layer 108 to improve the injection efficiency of holes and reduce electron leakage, thereby improving the performance of the deep ultraviolet LED epitaxial wafer 100; the unintentional doping part can maintain the intrinsic characteristics of the material and avoid excessive impurities from having an adverse effect on the device performance. At the same time, the unintentional doping part can also play a buffering role, reducing the interface effect between the N-type doping part and the P-type doping part.

[0040] In the embodiment of the present invention, the quantum well active layer 106 includes n potential well layers, where n≥1 and n is a positive integer; the P-type impurity concentration in the (n-1) potential well layers arranged along the growth direction of the quantum well active layer 106 is lower than 5E17cm -3 The P-type impurity concentration in the nth potential well layer arranged along the growth direction of the quantum well active layer 106 is lower than 1E18cm -3 Among them, a lower P-type impurity concentration can improve the stability and reliability of the deep ultraviolet LED epitaxial wafer 100. P-type impurities may cause material degradation and performance degradation. By controlling the P-type impurity concentration, this effect can be reduced and the service life of the deep ultraviolet LED epitaxial wafer 100 can be extended.

[0041] In the embodiment of the present invention, the electron blocking layer 108 is disposed on the impurity absorption layer 107, and the growth temperature of the electron blocking layer 108 ranges from 700°C to 1100°C; wherein the electron blocking layer 108 is a single-layer Mg-doped AlGaN structure, which uses bismuthocene magnesium as a dopant.

[0042] In an embodiment of the present invention, the hole injection layer 109 is arranged on the electron blocking layer 108, and the growth temperature range of the hole injection layer 109 is between 700°C and 1100°C; wherein, the material of the hole injection layer 109 is P-type doped AlGaN material, the percentage of the aluminum component content in the hole injection layer 109 is between 0 and 100%, the thickness range of the hole injection layer 109 is between 1nm and 50nm, and the hole injection layer 109 uses dicyclopentadienyl magnesium as a dopant.

[0043] Preferably, the hole injection layer 109 is a whole layer of Mg doped with a doping concentration of 1E17 cm -3 ~1E19cm -3 .

[0044] In an embodiment of the present invention, the ohmic contact layer 110 is disposed on the hole injection layer 109, and the growth temperature range of the ohmic contact layer 110 is between 650°C and 950°C; wherein, the material of the ohmic contact layer 110 is P-type doped GaN material, the percentage of the aluminum component content in the ohmic contact layer 110 is between 0 and 100%, the thickness range of the ohmic contact layer 110 is between 1nm and 20nm, and the ohmic contact layer 110 uses dicyclopentadienyl magnesium as a dopant.

[0045] Furthermore, in an embodiment of the present invention, the deep ultraviolet LED epitaxial wafer 100 also includes an N-type electrode 111 and a P-type electrode 112; wherein a step-like structure is formed between the current expansion layer 105 and the electron injection layer 104, and the area of ​​the current expansion layer 105 is smaller than the area of ​​the electron injection layer 104, the P-type electrode 112 is arranged on the ohmic contact layer 110, and the N-type electrode 111 is arranged at the step structure of the electron injection layer 104.

[0046] Accordingly, the embodiment of the present invention also provides a method for preparing a deep ultraviolet LED epitaxial wafer 100, which is performed in a MOCVD (Metal-organic Chemical Vapor Deposition) device. Figure 1 as well as Figure 2 , Figure 2 for Figure 2 The process flow chart of the epitaxial growth method of the deep ultraviolet LED epitaxial wafer 100 provided in the embodiment of the present invention; specifically, the epitaxial growth method includes: S10 , epitaxially growing a buffer layer 102 , an intrinsic layer 103 , an electron injection layer 104 , a current spreading layer 105 and a quantum well active layer 106 in sequence on a substrate 101 .

[0047] Specifically, step S10 also includes: First, a substrate 101 is provided, and the substrate 101 is made of sapphire material; Secondly, at a growth temperature of 400° C. to 800° C., an AlN buffer layer 102 is epitaxially grown on the substrate 101 , with a thickness of 10 nm to 50 nm; Then, the temperature is raised to 1200° C. to 1400° C., and an intrinsic layer 103 made of AlN is epitaxially grown on the buffer layer 102 , with a thickness of 500 nm to 4000 nm; Then, the temperature is lowered to 800° C. to 1200° C., and an electron injection layer 104 made of Si-doped AlGaN is epitaxially grown on the intrinsic layer 103 , wherein the Al component mass content is 20% to 90% and the thickness is 500 nm to 4000 nm; After that, the temperature is lowered to 700°C to 1100°C, and a current spreading layer 105 is epitaxially grown on the electron injection layer 104. The material of the current spreading layer 105 is non-intentionally doped AlGaN, the Al component mass content of which is 20% to 90%, and the thickness of which is 10nm to 300nm.

[0048] Finally, the temperature is kept constant at 700°C to 1100°C, and a quantum well active layer 106 is epitaxially grown on the current spreading layer 105. The quantum well active layer 106 includes at least one potential well layer and at least two potential well layers that are alternately arranged. Each potential well layer is inserted between two adjacent potential barrier layers, and the materials of the potential well layer and the potential well layer are both AlGaN.

[0049] S20 , epitaxially growing an impurity absorption layer 107 on the quantum well active layer 106 , wherein the material of the impurity absorption layer 107 is AlGaN, and at least a portion of the impurity absorption layer 107 is unintentionally doped.

[0050] Specifically, step S20 also includes: S201, maintaining the temperature or cooling it to 500° C. to 900° C., stopping the introduction of nitrogen and ammonia, and retaining hydrogen for annealing, the annealing time is 1 min to 60 min; wherein, performing hydrogen annealing for 1 min to 60 min before the growth of the impurity absorption layer 107 can remove oxides and impurities on the surface of the material, improve the surface quality of the material, and hydrogen annealing can also promote the diffusion and recombination of atoms, and improve the crystal structure of the material; S202, keeping the temperature constant, epitaxially growing an impurity absorption layer 107 on the quantum well active layer 106; S203, maintaining the temperature or cooling it to 500°C~900°C, stopping the introduction of hydrogen and ammonia, retaining nitrogen for annealing, and the annealing time is 1min~60min; performing nitrogen annealing for 1min~60min after the growth of the impurity absorption layer 107 is completed can stabilize the structure of the material and reduce defects and stress; nitrogen is an inert gas and will not chemically react with the material, so the material can be annealed without introducing new impurities.

[0051] S30 , epitaxially growing the electron blocking layer 108 , the hole injection layer 109 and the ohmic contact layer 110 in sequence on the impurity absorption layer 107 .

[0052] Specifically, step S30 also includes: First, the temperature is raised to 700° C. to 1100° C., and an electron blocking layer 108 is epitaxially grown on the impurity absorption layer 107; Secondly, keeping the temperature constant, epitaxially grow the hole injection layer 109 on the electron blocking layer 108; Afterwards, the temperature is lowered to 650° C. to 950° C., and an ohmic contact layer 110 is epitaxially grown on the hole injection layer 109 .

[0053] Afterwards, an N-type electrode 111 is disposed at the step structure of the current spreading layer 105 , and the N-type electrode 111 is disposed opposite to and spaced from the current spreading layer 105 ; finally, a P-type electrode 112 is formed on the ohmic contact layer 110 .

[0054] The technical solution of the present application is now described in conjunction with specific embodiments.

[0055] Embodiment 1 of the present invention: The film structure of the deep ultraviolet LED epitaxial wafer 100 provided in Example 1 of the present invention is shown below in order along the growth direction: Substrate 101, made of sapphire material; The buffer layer 102 is made of AlN and has a thickness of 20 nm; The intrinsic layer 103 is made of AlN and has a thickness of 2000 nm; The electron injection layer 104 is made of Si-doped AlGaN material, with an Al component mass content of 60% and a thickness of 1500 nm; The current spreading layer 105 is made of non-intentionally doped AlGaN material, with an Al component mass content of 50% and a thickness of 100 nm; The quantum well active layer 106 includes at least one potential well layer and at least two potential barrier layers which are alternately arranged, each potential well layer is inserted between two adjacent potential barrier layers, and the number of cycles is 10; the material of the potential barrier layer is aluminum gallium nitride, the mass content of the Al component is 60%, and the thickness of the potential barrier layer is 10nm; the material of the potential well layer is aluminum gallium nitride, the mass content of the Al component is 45%, and the thickness of the potential well layer is 2nm; The impurity absorption layer 107 is an AlGaN layer with a gradient Al component and a thickness of 10 nm; wherein the impurity absorption layer 107 includes an N-type doped portion close to the quantum well active layer 106, a P-type doped portion close to the electron blocking layer 108, and an unintentionally doped portion between the N-type doped portion and the P-type doped portion; wherein the material of the N-type doped portion is Si-doped AlGaN material, the Al component mass content is 70%, the thickness is 4 nm, and the doping concentration is 1E18 cm -3 The material of the unintentionally doped part is an unintentionally doped AlGaN material, with an Al component mass content of 75% and a thickness of 4nm; the material of the P-type doped part is a Mg-doped AlGaN material, with an Al component mass content of 80%, a thickness of 2nm, and a doping concentration of 2E18cm -3 ; A 5-minute hydrogen annealing is performed before the growth of the impurity absorption layer 107, and a 10-minute nitrogen annealing is performed after the growth of the impurity absorption layer 107 is completed; The electron blocking layer 108 is a single-layer Mg-doped AlGaN structure with a thickness of 10 nm; The hole injection layer 109 is made of Mg-doped AlGaN material, with an Al component mass content of 40% and a thickness of 20 nm, and uses bis(cyclopentadienyl)magnesium as a P-type dopant; The ohmic contact layer 110 is made of Mg-doped GaN material and has a thickness of 10 nm.

[0056] Furthermore, a conventional method is used to set an N-type electrode 111 on the electron injection layer 104, and a P-type electrode 112 made of the same material as the N-type electrode 111 is set on the ohmic contact layer 110 to form a complete epitaxial chip structure, and the specific process is not described here. Among them, the N-type electrode 111 and the P-type electrode 112 are both multi-layer composite metal materials.

[0057] Comparative Example: The deep ultraviolet LED epitaxial wafer 100 prepared by conventional process, the film layer structure of the deep ultraviolet LED epitaxial wafer 100 provided in the comparative example is roughly the same as the structure and material of Example 1 of the present invention, the only difference is that: the impurity absorption layer 107 is not set between the quantum well active layer 106 and the electron blocking layer 108.

[0058] Furthermore, the optical power of the deep ultraviolet LED epitaxial wafer 100 prepared in Example 1 of the present invention and the voltage of the deep ultraviolet LED epitaxial wafer 100 prepared in the comparative example at a current of 100 mA and the test results are shown in Table 1 below: Table 1 Test results of Example 1 of the present invention and comparative example sample Optical power at 100mA Voltage at 100mA Example 1 34.8mW 5.98V Comparative Example 27.2mW 6.23V Specifically, it can be seen from Table 1 above that under the test condition of 100mA, the deep ultraviolet LED epitaxial wafer 100 prepared in Example 1 of the present invention has higher optical power and lower operating voltage than the control example, which proves that the introduction of the impurity absorption layer 107 is beneficial to the luminous efficiency of the deep ultraviolet LED epitaxial wafer 100.

[0059] See also Figure 3 as well as Figure 4 , Figure 3 The distribution diagram of element contents in each epitaxial layer near the quantum well active layer 106 and the electron blocking layer 108 in the deep ultraviolet LED epitaxial wafer 100 provided in Example 1 of the present invention; Figure 4 The element content distribution diagram of each epitaxial layer near the quantum well active layer 106 and the electron blocking layer 108 in the deep ultraviolet LED epitaxial wafer 100 provided as a comparative example; Figure 3 as well as Figure 4 By comparison, it can be seen that as the depth Depth of the deep ultraviolet LED epitaxial wafer 100 increases, the Si impurity concentration in the depth region of 100nm~110nm (the region where the electron blocking layer 108 is located) of Example 1 of the present invention is 1E16cm -3 ~1E17cm -3 , while the Si impurity concentration in the depth region of 100nm~110nm in the comparative example is 1E18cm -3 ~1E19cm -3 ; The Mg impurity concentration in the depth region of 140nm~150nm (the region where the quantum well active layer 106 is located) of Example 1 of the present invention is 1E16cm -3 ~1E17cm -3 , while the Mg impurity concentration in the depth region of 140nm~150nm in the comparative example is 1E17cm -3 ~1E18cm -3 .

[0060] The above comparison results show that the deep ultraviolet LED epitaxial wafer 100 provided in Example 1 of the present invention can hinder the mutual diffusion of Mg from the P-type epitaxial layer and Si from the N-type epitaxial layer by setting the impurity absorption layer 107 between the quantum well active layer 106 and the electron blocking layer 108, thereby improving the radiation recombination efficiency of the quantum well active layer 106 and ultimately improving the luminous efficiency of the deep ultraviolet LED epitaxial wafer 100.

[0061] In summary, different from the prior art, the present invention provides a deep ultraviolet LED epitaxial wafer 100 and an epitaxial growth method thereof, wherein the deep ultraviolet LED epitaxial wafer 100 comprises a substrate 101, a buffer layer 102, an intrinsic layer 103, an electron injection layer 104, a current expansion layer 105, a quantum well active layer 106, an electron blocking layer 108, a hole injection layer 109 and an ohmic contact layer 110 which are sequentially stacked along a growth direction, wherein an impurity absorption layer 107 is further arranged between the quantum well active layer 106 and the electron blocking layer 108, wherein the material of the impurity absorption layer 107 is AlGaN, and at least a portion of the impurity absorption layer 107 is unintentionally doped; An impurity absorption layer 107 is arranged between the electron injection layer 104 and the electron blocking layer 108, and at least a portion of the impurity absorption layer 107 is unintentionally doped to form an N-type impurity concentration gradient between the electron injection layer 104 and the impurity absorption layer 107, and a P-type impurity concentration gradient is formed between the hole injection layer 109 and the impurity absorption layer 107. The above-mentioned N-type impurity concentration gradient and P-type impurity concentration gradient will generate a diffusion driving force, thereby promoting the diffusion of N-type impurities and P-type impurities into the impurity absorption layer 107, and then the impurity absorption layer 107 can absorb N-type impurities and P-type impurities, further improve the radiation recombination efficiency of the quantum well active layer 106, and finally improve the luminous efficiency of the deep ultraviolet LED epitaxial wafer 100.

[0062] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0063] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A deep ultraviolet LED epitaxial wafer, characterized in that: It includes a substrate, a buffer layer, an intrinsic layer, an electron injection layer, a current expansion layer, a quantum well active layer, an electron blocking layer, a hole injection layer and an ohmic contact layer which are sequentially stacked along a growth direction; Wherein, an impurity absorption layer is further arranged between the quantum well active layer and the electron blocking layer; the material of the impurity absorption layer is AlGaN, and at least a part of the impurity absorption layer is unintentionally doped.

2. The deep ultraviolet LED epitaxial wafer according to claim 1, characterized in that: The impurity absorption layer is a single-layer AlGaN structure, the Al component mass content of the impurity absorption layer is 20% to 90%, and the thickness of the impurity absorption layer is 1nm to 500nm.

3. The deep ultraviolet LED epitaxial wafer according to claim 2, characterized in that: The Al component content of the impurity absorption layer increases linearly along the growth direction; the Al component mass content at the contact interface between the impurity absorption layer and the quantum well active layer is 20% to 70%, and the Al component mass content at the contact interface between the impurity absorption layer and the electron blocking layer is 40% to 90%.

4. The deep ultraviolet LED epitaxial wafer according to claim 1, characterized in that: The impurity absorption layer includes a plurality of periodic structures, each of which includes a first sublayer and a second sublayer stacked in sequence along the growth direction, and the material of the first sublayer is Al a Ga 1-a N, the material of the second sublayer is Al b Ga 1-b N, a is the Al component mass content of the first sub-layer, b is the Al component mass content of the second sub-layer, and a and b satisfy the following relationship: 20%≤b≤a≤90%; The thickness of the first sub-layer is 1 nm to 20 nm, the thickness of the second sub-layer is 2 nm to 20 nm, and the number of periods of the impurity absorption layer is 2 to 50.

5. The deep ultraviolet LED epitaxial wafer according to any one of claims 2 to 4, characterized in that: The impurity absorption layer is a whole layer that is not intentionally doped.

6. The deep ultraviolet LED epitaxial wafer according to any one of claims 2 to 4, characterized in that: The impurity absorption layer includes an N-type doped portion close to the quantum well active layer, a P-type doped portion close to the electron blocking layer, and an unintentionally doped portion between the N-type doped portion and the P-type doped portion; Wherein, the doping concentration of the N-type doping part is 1E16cm -3 ~5E18cm -3 The doping concentration of the P-type doping part is 1E16cm -3 ~5E18cm -3 .

7. The deep ultraviolet LED epitaxial wafer according to claim 1, characterized in that: The quantum well active layer includes at least one potential well layer and at least two potential barrier layers which are alternately arranged, each potential well layer is inserted between two adjacent potential barrier layers, and the quantum well active layer includes n potential well layers, where n≥1 and n is a positive integer; The concentration of P-type impurities in the (n-1) potential well layers arranged along the growth direction of the quantum well active layer is lower than 5E17cm -3 The P-type impurity concentration in the nth potential well layer arranged along the growth direction of the quantum well active layer is lower than 1E18cm -3 .

8. The deep ultraviolet LED epitaxial wafer according to claim 1, characterized in that: The N-type impurity concentration in the electron blocking layer is lower than 8E17cm -3 The N-type impurity concentration in the hole injection layer and the ohmic contact layer is lower than 5E17cm -3 .

9. An epitaxial growth method for a deep ultraviolet LED epitaxial wafer as claimed in claim 1, characterized in that: The epitaxial growth method comprises: S10, epitaxially growing the buffer layer, the intrinsic layer, the electron injection layer, the current spreading layer and the quantum well active layer in sequence on the substrate; S20, epitaxially growing the impurity absorption layer on the quantum well active layer, wherein the material of the impurity absorption layer is AlGaN, and at least a portion of the impurity absorption layer is unintentionally doped; S30, epitaxially growing the electron blocking layer, the hole injection layer and the ohmic contact layer in sequence on the impurity absorption layer.

10. The epitaxial growth method of a deep ultraviolet LED epitaxial wafer according to claim 9, characterized in that: Before performing the S20 step, the method also includes: introducing H2 into the growth furnace to anneal the quantum well active layer, the annealing temperature is 500°C~900°C, and the annealing time is 1min~60min; before performing the S30 step, the method also includes: introducing N2 into the growth furnace to anneal the impurity absorption layer, the annealing temperature is 500°C~900°C, and the annealing time is 1min~60min.

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