An epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs

Abstract

The present invention discloses an epitaxial growth method for improving the hole activation efficiency of a deep ultraviolet LED, comprising the following steps: S1, preparing a deep ultraviolet LED epitaxial wafer; S2, in a nitrogen atmosphere, performing in-situ annealing on the deep ultraviolet LED epitaxial wafer for several cycles; in a single in-situ annealing cycle of step S2, any process parameter in the cavity pressure or the nitrogen flow rate changes in a trend of first decreasing and then increasing. The present invention not only improves the activation efficiency of Mg by setting a periodic annealing stage and adjusting the nitrogen flow rate or the cavity pressure, but also can prompt the byproducts after H dissociation to be discharged from the reaction chamber in time, effectively preventing the secondary bonding of Mg and H, and improving the luminous efficiency of the deep ultraviolet LED device.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronics, and in particular to an epitaxial growth method for improving the hole activation efficiency of a deep ultraviolet LED. Background Art

[0002] At present, as an outstanding representative of wide bandgap semiconductor materials, group III nitrides have realized efficient blue-green light emitting diodes (LEDs), lasers and other solid-state light source devices, and have achieved great success in applications such as flat panel displays and white light illumination. In the past decade, people have hoped to apply this efficient luminescent material to the ultraviolet band to meet the growing demand for ultraviolet light sources.

[0003] For nitride LEDs, whether blue-green LEDs or ultraviolet LEDs, Mg is used as a P-type dopant. During the epitaxial production process, Mg will form a complex with H decomposed from ammonia or hydrogen used in the growth, so Mg doping needs to be activated to form carriers. The commonly used activation method is to pass nitrogen into the reaction chamber after the LED epitaxial structure growth is completed, so that the cavity forms a nitrogen atmosphere, and annealing in a nitrogen atmosphere can break the Mg-H bond to form holes. For deep ultraviolet LEDs, due to the increase in Al component, the activation energy of Mg in AlGaN will also increase, and the activation efficiency will also decrease. In addition, when the Mg-H bond is broken, the dissociated Mg and H may form a secondary bond. That is, under high Al component content, it is difficult to achieve full activation of Mg doping by using traditional nitrogen annealing methods, thereby inhibiting the carrier injection efficiency, and ultimately making it difficult to improve the luminous efficiency of LED devices. Therefore, it is necessary to provide a new deep ultraviolet LED preparation solution to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide an epitaxial growth method and a preparation method thereof for improving the hole activation efficiency of deep ultraviolet LEDs, so as to solve the problem in the prior art that the p-type doping efficiency in high Al component AlGaN materials is low, thereby making the luminous efficiency of the device low.

[0005] To solve the above technical problems, the present invention provides an epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs, comprising the following steps: S1, preparing a deep ultraviolet LED epitaxial wafer; S2, performing in-situ annealing on the deep ultraviolet LED epitaxial wafer for several cycles under a nitrogen atmosphere; in a single in-situ annealing cycle of step S2, any process parameter in the chamber pressure or the nitrogen flow rate shows a trend of first decreasing and then increasing.

[0006] Among them, step S2 includes four stages that are executed in sequence: a first constant annealing stage, a descending stage, a second constant annealing stage and an ascending stage; and it is satisfied that the chamber pressure in the first constant annealing stage is greater than the chamber pressure in the second constant annealing stage, or the nitrogen flow rate in the first constant annealing stage is greater than the nitrogen flow rate in the second constant annealing stage.

[0007] Preferably, in step S2, the annealing temperature is 800-950° C., and the annealing time is 1-40000 s.

[0008] Preferably, in step S2, the in-situ annealing is performed for a period of 1 to 10.

[0009] In one implementation mode, in a single in-situ annealing cycle of step S2, the nitrogen flow rate is constant, and the chamber pressure shows a trend of first decreasing and then increasing; the chamber pressure in the first constant annealing stage is greater than the chamber pressure in the second constant annealing stage, the chamber pressure in the descending stage decreases linearly from the chamber pressure in the first constant annealing stage to the chamber pressure in the second constant annealing stage, and the chamber pressure in the ascending stage increases linearly from the chamber pressure in the second constant annealing stage to the chamber pressure in the first constant annealing stage.

[0010] Furthermore, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 1:1:1:1; the chamber pressure of the first constant annealing stage is constant at 200-500 mbar, and the chamber pressure of the second constant annealing stage is constant at 50-190 mbar.

[0011] In one embodiment, in a single in-situ annealing cycle of step S2, the chamber pressure is constant, and the nitrogen flow rate shows a trend of first decreasing and then increasing; the nitrogen flow rate in the first constant annealing stage is greater than the nitrogen flow rate in the second constant annealing stage, the nitrogen flow rate in the descending stage linearly decreases from the nitrogen flow rate in the first constant annealing stage to the nitrogen flow rate in the second constant annealing stage, and the nitrogen flow rate in the ascending stage linearly increases from the nitrogen flow rate in the second constant annealing stage to the nitrogen flow rate in the first constant annealing stage.

[0012] Furthermore, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 4:1:2:1; the nitrogen flow rate of the first constant annealing stage is constant at 50-70slm, and the nitrogen flow rate of the second constant annealing stage is constant at 30-45slm.

[0013] In one embodiment, in a single in-situ annealing cycle of step S2, the chamber pressure and the nitrogen flow rate change synchronously with a trend of first decreasing and then increasing; the chamber pressure of the first constant annealing stage is greater than the chamber pressure of the second constant annealing stage, and the nitrogen flow rate of the first constant annealing stage is greater than the nitrogen flow rate of the second constant annealing stage; the chamber pressure in the descending stage linearly decreases from the chamber pressure of the first constant annealing stage to the chamber pressure of the second constant annealing stage, and at the same time, the nitrogen flow rate in the descending stage linearly decreases from the nitrogen flow rate of the first constant annealing stage to the nitrogen flow rate of the second constant annealing stage; the chamber pressure in the ascending stage linearly increases from the chamber pressure of the second constant annealing stage to the chamber pressure of the first constant annealing stage, and at the same time, the nitrogen flow rate in the ascending stage linearly increases from the nitrogen flow rate of the second constant annealing stage to the nitrogen flow rate of the first constant annealing stage.

[0014] Furthermore, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 2:1:2:1; the chamber pressure of the first constant annealing stage is constant at 200-500 mbar, and the nitrogen flow rate is constant at 50-70 slm; the chamber pressure of the second constant annealing stage is constant at 50-190 mbar, and the nitrogen flow rate is constant at 30-45 slm.

[0015] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides an epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs, which not only improves the activation efficiency of Mg but also promotes the timely discharge of byproducts after H dissociation from the reaction chamber, effectively preventing the secondary bonding of Mg and H, and improving the luminous efficiency of deep ultraviolet LED devices by setting a periodic annealing stage and adjusting the nitrogen flow rate or the cavity pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a process flow chart of an embodiment of an epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs in the present invention;

[0017] Figure 2 is a curve diagram of process parameter changes in a single in-situ annealing cycle in Example 1 of the present invention;

[0018] Figure 3 is a curve diagram of process parameter changes in a single in-situ annealing cycle in Example 2 of the present invention;

[0019] Figure 4 It is a curve diagram of process parameter changes in a single in-situ annealing cycle in Example 3 of the present invention. DETAILED DESCRIPTION

[0020] 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.

[0021] See also Figure 1 , Figure 1 The process flow chart of an embodiment of the epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs in the present invention is as follows:

[0022] S1, prepare deep ultraviolet LED epitaxial wafer. In this step, Al intrinsic layer, n-type AlGaN electron injection layer, current expansion layer, multi-quantum well active layer, electron blocking layer and p-type AlGaN hole injection layer are grown in sequence on the sapphire substrate to obtain deep ultraviolet LED epitaxial wafer; conventional MOCVD and other processes can be used to prepare the epitaxial wafer, and the specific steps are as follows:

[0023] S11, growing an AlN low-temperature buffer layer at 400°C to 800°C, with a thickness of 10nm to 50nm.

[0024] S12, raising the temperature to 1200°C to 1400°C to grow an AlN intrinsic layer with a thickness of 500nm to 4000nm.

[0025] S13, cooling to 800°C to 1200°C, growing an n-type AlGaN electron injection layer, wherein the Al component is 20% to 90% and the thickness is 500nm to 4000nm.

[0026] S14, cooling to 700°C-1100°C, and sequentially growing a current expansion layer and a quantum well active region; wherein the barrier Al component of the quantum well active region is 40%-90%, with a thickness of 1nm-30nm, and the potential well Al component is 30%-80%, with a thickness of 0.1nm-5nm.

[0027] S15, raising the temperature to 700°C to 1100°C to grow an electron blocking layer, wherein the electron blocking layer has an Al component of 50% to 100% and a thickness of 0.1nm to 200nm.

[0028] S16, cooling to 600-1100°C, growing a p-type AlGaN hole injection layer, wherein the Al component is 20%-60%, the thickness is 0.1nm-50nm. The dopant is Mg, and the doping concentration is 1E18-5E20 cm -3 .

[0029] S2, in a nitrogen atmosphere, the deep ultraviolet LED epitaxial wafer is subjected to several cycles of in-situ annealing; in a single in-situ annealing cycle of step S2, any process parameter of the chamber pressure or the nitrogen flow rate shows a trend of first decreasing and then increasing. Among them, the annealing temperature is 800-950°C, the annealing time is 1-40000s, and the execution cycle of the in-situ annealing is 1-10.

[0030] Specifically, in step S2, each in-situ annealing cycle includes four stages that are performed sequentially: a first constant annealing stage, a descending stage, a second constant annealing stage, and an ascending stage (corresponding to Figures 2 to 4 The chamber pressure of the first constant annealing stage is greater than the chamber pressure of the second constant annealing stage, or the nitrogen flow rate of the first constant annealing stage is greater than the nitrogen flow rate of the second constant annealing stage. The three settings are as follows:

[0031] 1) If Figure 2 As shown, in the single in-situ annealing cycle of step S2, the nitrogen flow rate is constant, and the chamber pressure shows a trend of first decreasing and then increasing; the chamber pressure in the first constant annealing stage is greater than the chamber pressure in the second constant annealing stage, the chamber pressure in the descending stage decreases linearly from the chamber pressure in the first constant annealing stage to the chamber pressure in the second constant annealing stage, and the chamber pressure in the ascending stage increases linearly from the chamber pressure in the second constant annealing stage to the chamber pressure in the first constant annealing stage. In this setting, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 1:1:1:1; the chamber pressure in the first constant annealing stage is constant at 200-500mbar, and the chamber pressure in the second constant annealing stage is constant at 50-190mbar.

[0032] 2) If Figure 3 As shown, in the single in-situ annealing cycle of step S2, the chamber pressure is constant, and the nitrogen flow rate shows a trend of first decreasing and then increasing; the nitrogen flow rate in the first constant annealing stage is greater than the nitrogen flow rate in the second constant annealing stage, the nitrogen flow rate in the descending stage linearly decreases from the nitrogen flow rate in the first constant annealing stage to the nitrogen flow rate in the second constant annealing stage, and the nitrogen flow rate in the ascending stage linearly increases from the nitrogen flow rate in the second constant annealing stage to the nitrogen flow rate in the first constant annealing stage. In this setting, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 4:1:2:1; the nitrogen flow rate in the first constant annealing stage is constant at 50-70slm, and the nitrogen flow rate in the second constant annealing stage is constant at 30-45slm.

[0033] 3) If Figure 4As shown, in the single in-situ annealing cycle of step S2, the chamber pressure and the nitrogen flow rate change synchronously with a trend of first decreasing and then increasing; the chamber pressure in the first constant annealing stage is greater than the chamber pressure in the second constant annealing stage, and the nitrogen flow rate in the first constant annealing stage is greater than the nitrogen flow rate in the second constant annealing stage; the chamber pressure in the descending stage decreases linearly from the chamber pressure in the first constant annealing stage to the chamber pressure in the second constant annealing stage, and at the same time, the nitrogen flow rate in the descending stage decreases linearly from the nitrogen flow rate in the first constant annealing stage to the nitrogen flow rate in the second constant annealing stage; the chamber pressure in the ascending stage increases linearly from the chamber pressure in the second constant annealing stage to the chamber pressure in the first constant annealing stage, and at the same time, the nitrogen flow rate in the ascending stage increases linearly from the nitrogen flow rate in the second constant annealing stage to the nitrogen flow rate in the first constant annealing stage. In this setting, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 2:1:2:1; the chamber pressure of the first constant annealing stage is constant at 200-500 mbar, and the nitrogen flow rate is constant at 50-70 slm; the chamber pressure of the second constant annealing stage is constant at 50-190 mbar, and the nitrogen flow rate is constant at 30-45 slm.

[0034] For deep ultraviolet LEDs with high Al components, the activation energy of Mg in AlGaN increases, and the activation efficiency also decreases. During the annealing process, not only the degree of Mg-H bond breaking needs to be considered, but also the secondary bonding needs to be considered. The principle of the present invention is that by controlling the nitrogen flow rate or cavity pressure to make specific periodic changes, on the one hand, nitrogen is introduced into the reaction chamber to form a nitrogen atmosphere in the cavity, and annealing in a nitrogen atmosphere can break the Mg-H bond and form a hole; on the other hand, the byproducts after H dissociation are urged to be promptly removed from the reaction chamber to reduce secondary bonding. The two effects improve the overall activation efficiency of Mg, thereby improving the luminous efficiency of deep ultraviolet LED devices.

[0035] The effect of the above-mentioned epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs is characterized by specific examples below.

[0036] Example 1

[0037] The specific steps of the epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs in this embodiment are as follows:

[0038] The specific preparation steps of deep ultraviolet LED epitaxial wafer are as follows:

[0039] (1) A low-temperature buffer layer in an AlN intrinsic layer is grown on a sapphire substrate at 600°C with a thickness of 30 nm.

[0040] (2) The temperature is raised to 1200° C. to grow an AlN intrinsic layer on the buffer layer in the AlN intrinsic layer. The total thickness of the AlN intrinsic layer is 2000 nm.

[0041] (3) The temperature is lowered to 800° C., and an n-type AlGaN electron injection layer is grown on the AlN intrinsic layer, wherein the Al component percentage is 60% and the thickness is 1000 nm.

[0042] (4) Cooling to 750° C., and sequentially growing a current spreading layer and a quantum well active layer on the n-type AlGaN electron injection layer. The potential barrier thickness of the quantum well active layer is 15 nm and the Al component percentage in the potential barrier is 75%. The potential well thickness is 2 nm and the Al component percentage in the potential well is 60%.

[0043] (5) The temperature is lowered to 700° C., and an electron blocking layer is grown on the quantum well active layer, wherein the Al component percentage is 65% and the thickness is 100 nm.

[0044] (6) A p-type AlGaN hole injection layer was grown on the electron blocking layer at 800°C, with an Al component percentage of 50% and a thickness of 20 nm. Mg was used as a p-type dopant with a doping concentration of 1E18 to 5E20 cm -3 , a deep ultraviolet LED epitaxial wafer is prepared.

[0045] The prepared deep ultraviolet LED epitaxial wafer is further subjected to several cycles of in-situ annealing treatment, and the specific steps are as follows:

[0046] (7) First constant annealing stage: the chamber pressure is maintained at 300 mbr for 60 s.

[0047] (8) Decreasing stage: the chamber pressure is linearly reduced from 300 mbr to 100 mbr, and the pressure change time is 60 s.

[0048] (9) Second constant annealing stage: the chamber pressure is maintained at 100 mbr for 60 s.

[0049] (10) Ascending stage: the chamber pressure is linearly increased from 100 mbr to 300 mbr, and the pressure change time is 60 s.

[0050] (11) The time proportion of the four stages in each cycle is 1:1:1:1, and steps (7) to (10) are repeated. The number of repeated cycles is 4, during which the nitrogen flow rate is constantly set to 50 slm. After the in-situ annealing treatment is completed, an annealed epitaxial wafer sample is obtained.

[0051] Example 2

[0052] This embodiment is based on the preparation steps of Example 1, and only the in-situ annealing step is adjusted, and the other steps are consistent with Example 1. In this embodiment, the prepared deep ultraviolet LED epitaxial wafer is further subjected to several cycles of in-situ annealing, and the specific steps are as follows:

[0053] (7) First constant annealing stage: the nitrogen flow rate is maintained at 60 slm for 120 s.

[0054] (8) Decreasing stage: the nitrogen flow rate is linearly reduced from 60 slm to 40 slm, and the flow rate change time is 30 s.

[0055] (9) Second constant annealing stage: the nitrogen flow rate is maintained at 40 slm for 60 s.

[0056] (10) Ascending stage: the nitrogen flow rate is linearly increased from 40 slm to 60 slm, and the pressure rise time is 30 s.

[0057] (11) The time ratio of the four stages in each cycle is 4:1:2:1. Steps (7) to (10) are repeated for 4 cycles. During this period, the chamber pressure is constantly set to 200 mbr. After the in-situ annealing treatment is completed, an annealed epitaxial wafer sample is obtained.

[0058] Example 3

[0059] This embodiment is based on the preparation steps of Example 1, and only the in-situ annealing step is adjusted, and the other steps are consistent with Example 1. In this embodiment, the prepared deep ultraviolet LED epitaxial wafer is further subjected to several cycles of in-situ annealing, and the specific steps are as follows:

[0060] (7) First constant annealing stage: the chamber pressure is maintained at 300 mbr, the nitrogen flow rate is maintained at 60 slm, and the maintenance time is 80 s.

[0061] (8) Decreasing stage: the chamber pressure is linearly reduced from 300 mbr to 100 mbr, and the nitrogen flow rate is linearly reduced from 60 slm to 40 slm, with a flow rate change time of 40 s.

[0062] (9) Second constant annealing stage: the chamber pressure is maintained at 100 mbr, the nitrogen flow rate is maintained at 40 slm, and the maintenance time is 80 s.

[0063] (10) Rising stage: The chamber pressure is linearly increased from 100 mbr to 300 mbr, and the nitrogen flow rate is linearly increased from 40 slm to 60 slm, and the pressure rise time is 40 s.

[0064] (11) The time ratio of the four stages in each cycle is 2:1:2:1. Steps (7) to (10) are repeated for 4 cycles. During this period, the chamber pressure is constantly set to 200 slm. After the in-situ annealing treatment is completed, an annealed epitaxial wafer sample is obtained.

[0065] Comparative Example 1

[0066] This comparative example is based on the preparation steps of Example 1, and only the duration of each stage in the in-situ annealing step is adjusted, and the other steps are consistent with Example 1. Specifically, the duration of the four stages in each cycle is set to 60s, 60s, 120s, and 60s in sequence; that is, the time ratio of the four stages is 1:1:2:1.

[0067] Comparative Example 2

[0068] This comparative example is based on the preparation steps of Example 2, and only the duration of each stage in the in-situ annealing step is adjusted, and the other steps are consistent with Example 2. Specifically, the duration of the four stages in each cycle is set to 60s, 30s, 60s, and 30s in sequence; that is, the time ratio of the four stages is 2:1:2:1.

[0069] Comparative Example 3

[0070] This comparative example is based on the preparation steps of Example 3, and only the duration of each stage in the in-situ annealing step is adjusted, and the other steps are consistent with Example 3. Specifically, the duration of the four stages in each cycle is set to 40s, 40s, 40s, and 40s in sequence; that is, the time ratio of the four stages is 1:1:1:1.

[0071] Comparative Example 4

[0072] This comparative example is based on the preparation steps of Example 1, without the in-situ annealing treatment, and the other steps are consistent with Example 1.

[0073] The photoelectric performance test was performed on all samples of Examples 1 to 3 and Comparative Examples 1 to 4, and the in-situ annealing method and the photoelectric test data were statistically analyzed. The results are shown in Table 1.

[0074] Table 1

[0075]

[0076] By comparing the photoelectric performance test data of Examples 1 to 3 and Comparative Example 4 in Table 1, it can be seen that after the in-situ annealing treatment by the aforementioned three methods, the samples obtained in Examples 1 to 3 have higher light output powers than the samples without in-situ annealing treatment, and the operating voltage is also reduced. This proves that the present invention performs the aforementioned several cycles of in-situ annealing treatment after the epitaxial wafer is prepared, which is beneficial to improving the luminescence effect of the deep ultraviolet LED.

[0077] The three groups of in-situ annealing methods in Table 1, Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, are compared respectively. Each comparative example only adjusts the time proportion of each stage for the embodiment of the same in-situ annealing method, but the photoelectric test effects of the comparative examples after adjustment are not as good as those of the corresponding embodiments. When the time proportion of each stage or other process parameters change, it may lead to incomplete annealing, insufficient Mg-H bond breaking, or byproducts after H dissociation are not discharged in time, resulting in secondary bonding, etc., which ultimately leads to poor photoelectric effect of the sample. Therefore, it is explained that the time proportion of each stage in the in-situ annealing cycle of the present invention needs to be specifically set based on the selection of different in-situ annealing settings to obtain better photoelectric effect.

[0078] Different from the prior art, the present invention provides an epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs. By setting a periodic annealing stage and adjusting the nitrogen flow rate or cavity pressure, not only the activation efficiency of Mg is improved, but also the byproducts after H dissociation can be promptly discharged from the reaction chamber, effectively preventing the secondary bonding of Mg and H, and improving the luminous efficiency of deep ultraviolet LED devices.

[0079] The above-mentioned 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 variations 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 subject to the attached claims.

Claims

1. An epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs, characterized in that: The steps include: S1, preparing deep ultraviolet LED epitaxial wafer; S2, performing several cycles of in-situ annealing on the deep ultraviolet LED epitaxial wafer in a nitrogen atmosphere; In the single in-situ annealing cycle of step S2, any process parameter of the chamber pressure or the nitrogen flow rate shows a trend of first decreasing and then increasing; The step S2 includes four stages that are executed in sequence: a first constant annealing stage, a descending stage, a second constant annealing stage, and an ascending stage; and the chamber pressure in the first constant annealing stage is greater than the chamber pressure in the second constant annealing stage, or the nitrogen flow rate in the first constant annealing stage is greater than the nitrogen flow rate in the second constant annealing stage; In the single in-situ annealing cycle of step S2, any of the following methods is used for setting: A1, in the single in-situ annealing cycle of the step S2, the nitrogen flow rate is constant, and the chamber pressure shows a trend of first decreasing and then increasing; the chamber pressure in the first constant annealing stage is greater than the chamber pressure in the second constant annealing stage, the chamber pressure in the descending stage decreases linearly from the chamber pressure in the first constant annealing stage to the chamber pressure in the second constant annealing stage, and the chamber pressure in the ascending stage increases linearly from the chamber pressure in the second constant annealing stage to the chamber pressure in the first constant annealing stage; A2, in the single in-situ annealing cycle of the step S2, the chamber pressure is constant, and the nitrogen flow rate shows a trend of first decreasing and then increasing; the nitrogen flow rate in the first constant annealing stage is greater than the nitrogen flow rate in the second constant annealing stage, the nitrogen flow rate in the descending stage linearly decreases from the nitrogen flow rate in the first constant annealing stage to the nitrogen flow rate in the second constant annealing stage, and the nitrogen flow rate in the ascending stage linearly increases from the nitrogen flow rate in the second constant annealing stage to the nitrogen flow rate in the first constant annealing stage; A3, in the single in-situ annealing cycle of the S2 step, the chamber pressure and the nitrogen flow rate change synchronously with a trend of first decreasing and then increasing; the chamber pressure of the first constant annealing stage is greater than the chamber pressure of the second constant annealing stage, and the nitrogen flow rate of the first constant annealing stage is greater than the nitrogen flow rate of the second constant annealing stage; the chamber pressure of the descending stage decreases linearly from the chamber pressure of the first constant annealing stage to the chamber pressure of the second constant annealing stage, and at the same time, the nitrogen flow rate of the descending stage decreases linearly from the nitrogen flow rate of the first constant annealing stage to the nitrogen flow rate of the second constant annealing stage; the chamber pressure of the ascending stage increases linearly from the chamber pressure of the second constant annealing stage to the chamber pressure of the first constant annealing stage, and at the same time, the nitrogen flow rate of the ascending stage increases linearly from the nitrogen flow rate of the second constant annealing stage to the nitrogen flow rate of the first constant annealing stage.

2. The epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs according to claim 1, characterized in that: In the step S2, the annealing temperature is 800-950°C, and the annealing time is 1-40000 s.

3. The epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs according to claim 1, characterized in that: In the step S2, the execution cycle of the in-situ annealing is 1 to 10.

4. The epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs according to claim 1, characterized in that: In the single in-situ annealing cycle of step S2, when the nitrogen flow rate is constant and the chamber pressure shows a trend of first decreasing and then increasing, the time proportions of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage are 1:1:1:1; The chamber pressure in the first constant annealing stage is constant at 200-500 mbar, and the chamber pressure in the second constant annealing stage is constant at 50-190 mbar.

5. The epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs according to claim 1, characterized in that: In the single in-situ annealing cycle of step S2, when the chamber pressure is constant and the nitrogen flow rate shows a trend of first decreasing and then increasing, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 4:1:2:1; The nitrogen flow rate in the first constant annealing stage is constant at 50-70 slm, and the nitrogen flow rate in the second constant annealing stage is constant at 30-45 slm.

6. The epitaxial growth method for improving the hole activation efficiency of deep ultraviolet LEDs according to claim 1, characterized in that: In the single in-situ annealing cycle of step S2, when the chamber pressure and the nitrogen flow rate change synchronously in a trend of first decreasing and then increasing, the time proportions of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage are 2:1:2:1; The chamber pressure in the first constant annealing stage is constant at 200-500 mbar, and the nitrogen flow rate is constant at 50-70 slm; The chamber pressure in the second constant annealing stage is constant at 50-190 mbar, and the nitrogen flow rate is constant at 30-45 slm.

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