CN115411157A - Epitaxial growth method for improving deep ultraviolet LED hole activation efficiency - Google Patents
Epitaxial growth method for improving deep ultraviolet LED hole activation efficiency Download PDFInfo
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Abstract
The invention discloses an epitaxial growth method for improving the hole activation efficiency of a deep ultraviolet LED, which comprises the following steps: s1, preparing a deep ultraviolet LED epitaxial wafer; s2, carrying out in-situ annealing on the deep ultraviolet LED epitaxial wafer for a plurality of periods in a nitrogen atmosphere; in the single in-situ annealing period in the step S2, any process parameter of the cavity pressure or the nitrogen flow changes in a trend of firstly decreasing and then increasing. According to the invention, by setting a periodic annealing stage and adjusting the nitrogen flow or the cavity pressure, the Mg activation efficiency is improved, byproducts generated after H dissociation can be promoted to be discharged out of the reaction cavity in time, secondary bonding of Mg and H is effectively prevented, and the luminous efficiency of the deep ultraviolet LED device is improved.
Description
Technical Field
The invention relates to the field of semiconductor photoelectricity, in particular to an epitaxial growth method for improving the hole activation efficiency of a deep ultraviolet LED.
Background
At present, group iii nitrides have been used as an outstanding representative of wide bandgap semiconductor materials, and have achieved high-efficiency solid-state light source devices such as blue-green light emitting diodes (i.e., LEDs), lasers, and the like, which have achieved great success in applications such as flat panel displays, white light illumination, and the like. In the last decade, it has been desired to apply such efficient luminescent materials in the ultraviolet band to meet the increasing demand of ultraviolet light sources.
For nitride LEDs, both blue-green LEDs and ultraviolet LEDs, mg is used as the P-type dopant, and during epitaxial production, mg forms a complex with H decomposed from ammonia or hydrogen used in growth, so Mg doping needs to be activated to form carriers. The common activating means is that after the growth of the LED epitaxial structure is completed, nitrogen is introduced into the reaction cavity to form a nitrogen atmosphere in the cavity, and the Mg-H bond can be broken to form a cavity after annealing in the nitrogen atmosphere. For the deep ultraviolet LED, the activation energy of Mg in AlGaN is increased along with the increase of the Al component, the activation efficiency is also reduced, and the Mg-H bond is broken, so that secondary bonding of the dissociated Mg and H is possible. Namely, under the condition of high Al component content, the full activation of Mg doping is difficult to realize by adopting the traditional nitrogen annealing means, so that the injection efficiency of current carriers is inhibited, and finally the luminous efficiency of an LED device is difficult to improve. It is therefore desirable to provide a new deep ultraviolet LED fabrication solution to solve the above problems.
Disclosure of Invention
The invention aims to provide an epitaxial growth method for improving the hole activation efficiency of a deep ultraviolet LED and a preparation method thereof, which are used for solving the problem that in the prior art, the p-type doping efficiency of an AlGaN material with a high Al component is low, so that the luminous efficiency of a device is low.
In order to solve the technical problem, the invention provides an epitaxial growth method for improving the hole activation efficiency of a deep ultraviolet LED, which comprises the following steps: s1, preparing a deep ultraviolet LED epitaxial wafer; s2, carrying out in-situ annealing on the deep ultraviolet LED epitaxial wafer for a plurality of periods in a nitrogen atmosphere; in the single in-situ annealing period of the step S2, any process parameter of the cavity pressure or the nitrogen flow changes in a trend of firstly decreasing and then increasing.
Wherein, the step S2 comprises four stages which are successively executed: a first constant annealing stage, a descending stage, a second constant annealing stage and an ascending stage; and the pressure of the cavity in the first constant annealing stage is larger than that in the second constant annealing stage, or the nitrogen flow in the first constant annealing stage is larger than that in the second constant annealing stage.
Preferably, in the step S2, the annealing temperature is 800-950 ℃, and the annealing time is 1-40000S.
Preferably, in the step S2, the in-situ annealing is performed for a period of 1 to 10.
In one embodiment, in the single in-situ annealing cycle in the step S2, the nitrogen flow is constant, and the cavity pressure changes in a trend of decreasing first and then increasing; the cavity pressure of the first constant annealing stage is greater than that of the second constant annealing stage, the cavity pressure of the descending stage is linearly decreased from the cavity pressure of the first constant annealing stage to the cavity pressure of the second constant annealing stage, and the cavity pressure of the ascending stage is linearly increased from the cavity pressure of the second constant annealing stage to the cavity pressure of the first constant annealing stage.
Further, the time ratio of the first constant annealing phase, the descending phase, the second constant annealing phase and the ascending phase is 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.
In one embodiment, in the single in-situ annealing cycle of the step S2, the pressure of the cavity is constant, and the nitrogen flow rate is changed in a trend of decreasing first 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 decreases linearly 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 increases linearly from the nitrogen flow rate in the second constant annealing stage to the nitrogen flow rate in the first constant annealing stage.
Further, the time ratio of the first constant annealing phase, the descending phase, the second constant annealing phase and the ascending phase is 4; 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.
In one embodiment, in the single in-situ annealing cycle of the step S2, the chamber pressure and the nitrogen flow rate are changed synchronously in a trend of decreasing first and then increasing; the cavity pressure of the first constant annealing stage is greater than that of the second constant annealing stage, and the nitrogen flow rate of the first constant annealing stage is greater than that of the second constant annealing stage; the cavity pressure in the descending stage is linearly decreased from the cavity pressure in the first constant annealing stage to the cavity pressure in the second constant annealing stage, and meanwhile, the nitrogen flow in the descending stage is linearly decreased from the nitrogen flow in the first constant annealing stage to the nitrogen flow in the second constant annealing stage; the chamber pressure in the rising stage is linearly increased from the chamber pressure in the second constant annealing stage to the chamber pressure in the first constant annealing stage, and the nitrogen flow rate in the rising stage is linearly increased from the nitrogen flow rate in the second constant annealing stage to the nitrogen flow rate in the first constant annealing stage.
Further, the time ratio of the first constant annealing phase, the descending phase, the second constant annealing phase and the ascending phase is 2; the pressure of the cavity in the first constant annealing stage is constant at 200-500 mbar, and the flow of nitrogen is constant at 50-70 slm; the cavity pressure in the second constant annealing stage is constant at 50-190 mbar, and the nitrogen flow is constant at 30-45 slm.
The invention has the beneficial effects that: different from the condition of the prior art, the epitaxial growth method for improving the deep ultraviolet LED hole activation efficiency provided by the invention has the advantages that the periodic annealing stage is set, the nitrogen flow or the cavity pressure is adjusted, the Mg activation efficiency is improved, byproducts generated after H dissociation can be promoted to be discharged out of a reaction cavity in time, secondary bonding of Mg and H is effectively prevented, and the luminous efficiency of a deep ultraviolet LED device is improved.
Drawings
FIG. 1 is a process flow diagram of one embodiment of an epitaxial growth method for improving deep ultraviolet LED hole activation efficiency in accordance with the present invention;
FIG. 2 is a graph of the variation of process parameters for a single in-situ annealing cycle in example 1 of the present invention;
FIG. 3 is a graph of the variation of process parameters for a single in-situ annealing cycle in example 2 of the present invention;
FIG. 4 is a graph of the variation of process parameters for a single in-situ anneal cycle in example 3 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Referring to fig. 1, fig. 1 is a process flow diagram of an embodiment of an epitaxial growth method for improving hole activation efficiency of a deep ultraviolet LED according to the present invention. The epitaxial growth method for improving the hole activation efficiency of the deep ultraviolet LED comprises the following steps:
s1, preparing a deep ultraviolet LED epitaxial wafer. In the step, an Al intrinsic layer, an n-type AlGaN electron injection layer, a current expansion layer, a multi-quantum well active layer, an electron blocking layer and a p-type AlGaN hole injection layer are sequentially grown on a sapphire substrate to prepare a deep ultraviolet LED epitaxial wafer; the preparation of the epitaxial wafer can be carried out by adopting the conventional MOCVD and other processes, and the specific steps are as follows:
s11, growing an AlN low-temperature buffer layer with the thickness of 10nm to 50nm at the temperature of 400 ℃ to 800 ℃.
S12, heating to 1200-1400 ℃, and growing an AlN intrinsic layer with the thickness of 500-4000 nm.
S13, cooling to 800-1200 ℃, and growing an n-type AlGaN electron injection layer, wherein the Al component of the n-type AlGaN electron injection layer is 20-90%, and the thickness of the n-type AlGaN electron injection layer is 500-4000 nm.
S14, cooling to 700-1100 ℃, 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%, the thickness is 1-30 nm, the potential well Al component is 30-80%, and the thickness is 0.1-5 nm.
S15, heating to 700-1100 ℃, and growing an electron blocking layer and an electron blocking layer, wherein the Al component of the electron blocking layer is 50-100%, and the thickness of the electron blocking layer is 0.1-200 nm.
And S16, cooling to 600-1100 ℃, and growing a p-type AlGaN hole injection layer, wherein the Al component of the p-type AlGaN hole injection layer is 20-60%, and the thickness of the p-type AlGaN hole injection layer is 0.1-50 nm. The doping agent is Mg, the doping concentration is 1E 18-5E20 cm -3 。
S2, carrying out in-situ annealing on the deep ultraviolet LED epitaxial wafer for a plurality of periods in a nitrogen atmosphere; in the single in-situ annealing period in the step S2, any process parameter of the cavity pressure or the nitrogen flow changes in a trend of firstly decreasing and then increasing. Wherein the annealing temperature is 800-950 ℃, the annealing time is 1-40000 s, and the execution period of in-situ annealing is 1-10.
Specifically, in the step S2, each in-situ annealing cycle includes four stages that are successively performed in sequence: a first constant annealing stage, a descending stage, a second constant annealing stage and an ascending stage (corresponding to stages 1 to 4 in fig. 2 to 4 in sequence); and the pressure of the cavity in the first constant annealing stage is larger than that in the second constant annealing stage, or the nitrogen flow in the first constant annealing stage is larger than that in the second constant annealing stage. The method specifically comprises the following three setting modes:
1) As shown in fig. 2, in the single in-situ annealing cycle of the step S2, the nitrogen flow is constant, and the cavity pressure is changed in a trend of decreasing first and then increasing; the cavity pressure of the first constant annealing stage is greater than that of the second constant annealing stage, the cavity pressure of the descending stage is linearly decreased from the cavity pressure of the first constant annealing stage to the cavity pressure of the second constant annealing stage, and the cavity pressure of the ascending stage is linearly increased from the cavity pressure of the second constant annealing stage to the cavity pressure of the first constant annealing stage. In the setting mode, the time ratio of the first constant annealing stage, the descending stage, the second constant annealing stage and the ascending stage is 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.
2) As shown in fig. 3, in the single in-situ annealing cycle of the step S2, the chamber pressure is constant, and the nitrogen flow rate is changed in a trend of decreasing first 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 is linearly decreased 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 is linearly increased 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; 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.
3) As shown in fig. 4, in the single in-situ annealing cycle of the step S2, the chamber pressure and the nitrogen flow rate are changed in a synchronous manner in a trend of decreasing first and then increasing; the cavity pressure of the first constant annealing stage is greater than the cavity 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 cavity pressure in the descending stage is linearly decreased from the cavity pressure in the first constant annealing stage to the cavity pressure in the second constant annealing stage, and meanwhile, the nitrogen flow in the descending stage is linearly decreased from the nitrogen flow in the first constant annealing stage to the nitrogen flow in the second constant annealing stage; the chamber pressure in the rising stage is linearly increased from the chamber pressure in the second constant annealing stage to the chamber pressure in the first constant annealing stage, and the nitrogen flow rate in the rising stage is linearly increased 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; the pressure of the cavity in the first constant annealing stage is constant at 200-500 mbar, and the flow of nitrogen is constant at 50-70 slm; the cavity pressure in the second constant annealing stage is constant at 50-190 mbar, and the nitrogen flow is constant at 30-45 slm.
For a deep ultraviolet LED with high Al component, the activation energy of Mg in AlGaN is increased, the activation efficiency is also reduced, and in the annealing treatment process, not only the fracture degree of Mg-H bonds but also secondary bonding needs to be considered. The principle of the invention is that specific periodic change is carried out by controlling the nitrogen flow or the cavity pressure, on one hand, nitrogen is introduced into the reaction cavity to form a nitrogen atmosphere in the cavity, and annealing is carried out in the nitrogen atmosphere, so that the Mg-H bond can be broken and a cavity is formed; on the other hand, by-products generated after H dissociation are promoted to be timely discharged from the reaction cavity, secondary bonding is reduced, and the activation efficiency of Mg is integrally improved under the two actions, so that the luminous efficiency of the deep ultraviolet LED device is improved.
The effect of the epitaxial growth method for improving the hole activation efficiency of the deep ultraviolet LED is characterized by the following specific embodiments.
Example 1
The specific steps of the epitaxial growth method for improving the hole activation efficiency of the deep ultraviolet LED in this embodiment are as follows:
the preparation method of the deep ultraviolet LED epitaxial wafer comprises the following specific steps:
(1) And growing a low-temperature buffer layer in the AlN intrinsic layer on the sapphire substrate at the temperature of 600 ℃, wherein the thickness of the low-temperature buffer layer is 30nm.
(2) And raising the temperature to 1200 ℃, and growing an AlN intrinsic layer on the buffer layer in the AlN intrinsic layer, wherein the total thickness of the AlN intrinsic layer is 2000nm.
(3) And cooling to 800 ℃, and growing an n-type AlGaN electron injection layer on the AlN intrinsic layer, wherein the Al component percentage is 60%, and the thickness is 1000nm.
(4) And cooling to 750 ℃, and sequentially growing a current expansion layer and a quantum well active layer on the n-type AlGaN electron injection layer, wherein the thickness of the potential barrier of the quantum well active layer is 15nm, the percentage of Al in the potential barrier is 75%, the thickness of the potential well is 2nm, and the percentage of Al in the potential well is 60%.
(5) And cooling to 700 ℃, and growing an electron barrier layer on the quantum well active layer, wherein the percentage of the Al component is 65%, and the thickness is 100nm.
(6) Growing a p-type AlGaN hole injection layer on the electron barrier layer at 800 ℃, wherein the Al component percentage is50 percent, 20nm in thickness, mg is adopted as a p-type dopant, and the doping concentration is 1E 18-5E20 cm -3 And preparing the deep ultraviolet LED epitaxial wafer.
Continuously carrying out in-situ annealing treatment on the prepared deep ultraviolet LED epitaxial wafer for a plurality of periods, and specifically comprising the following steps:
(7) A first constant annealing stage: the chamber pressure was maintained at 300mbr for 60s.
(8) A descending stage: the pressure of the cavity is linearly reduced from 300mbr to 100mbr, and the pressure changing time is 60s.
(9) A second constant annealing stage: the chamber pressure was maintained at 100mbr for 60s.
(10) And (3) a rising stage: the pressure of the cavity is increased linearly from 100mbr to 300mbr, and the pressure changing time is 60s.
(11) And (3) repeating the steps (7) to (10) at a time ratio of 1.
Example 2
This example was based on the preparation procedure of example 1, with only the steps of the in-situ annealing treatment being modified, and the other steps remaining the same as example 1. In this embodiment, the prepared deep ultraviolet LED epitaxial wafer is continuously subjected to in-situ annealing for several cycles, which specifically includes the following steps:
(7) A first constant annealing stage: the nitrogen flow was maintained at 60slm for 120s.
(8) A descending stage: the nitrogen flow was linearly reduced from 60slm to 40slm with a flow change time of 30s.
(9) A second constant annealing stage: the nitrogen flow was maintained at 40slm for 60s.
(10) And (3) a rising stage: the nitrogen flow was increased linearly from 40slm to 60slm with a 30s boost time.
(11) And (3) repeating the steps (7) to (10) at a time ratio of four stages in each period of 4.
Example 3
This example was based on the preparation procedure of example 1, with only the steps of the in-situ annealing treatment being modified, and the other steps remaining the same as example 1. In this embodiment, the prepared deep ultraviolet LED epitaxial wafer is continuously subjected to in-situ annealing for several cycles, which specifically includes the following steps:
(7) A first constant annealing stage: the chamber pressure was maintained at 300mbr, the nitrogen flow was maintained at 60slm, and the hold time was 80s.
(8) A descending stage: the chamber pressure was linearly reduced from 300 to 100mbr while the nitrogen flow was linearly reduced from 60 to 40slm with a flow change time of 40s.
(9) A second constant annealing stage: the chamber pressure was maintained at 100mbr, the nitrogen flow was maintained at 40slm, and the hold time was 80s.
(10) And (3) a rising stage: the chamber pressure was ramped from 100 to 300mbr, while the nitrogen flow was ramped from 40 to 60slm with a 40s boost time.
(11) And (3) repeating the steps (7) to (10) according to the time ratio of four stages in each period of 2.
Comparative example 1
This comparative example was based on the preparation procedure of example 1, and only the time length of each stage in the in-situ annealing treatment step was adjusted, and the other steps were kept consistent with example 1. Specifically, the time of four phases in each cycle is sequentially set to 60s, 120s, 60s; namely, the time ratio of the four phases is 1.
Comparative example 2
This comparative example was based on the preparation procedure of example 2, and only the time length of each stage in the step of in-situ annealing treatment was adjusted, and the other steps were kept consistent with example 2. Specifically, the time of four phases in each cycle is sequentially set to 60s, 30s, 60s, and 30s; namely, the time ratio of the four stages is 2.
Comparative example 3
This comparative example was based on the preparation procedure of example 3, and only the time duration of each stage in the in-situ annealing step was adjusted, and the other steps were kept the same as example 3. Specifically, the time of four phases in each cycle is set to 40s, 40s in sequence; namely, the time ratio of the four stages is 1.
Comparative example 4
This comparative example is based on the preparation procedure of example 1, without in situ annealing treatment, the other steps remaining identical to example 1.
All samples of examples 1 to 3 and comparative examples 1 to 4 were subjected to the photoelectric property test, and the in-situ annealing manner and the photoelectric test data were counted, and the results are shown in table 1.
TABLE 1
Comparing the photoelectric property test data of examples 1 to 3 in table 1 with that of comparative example 4, it can be seen that after the three in-situ annealing treatments, the light output power of the samples obtained in examples 1 to 3 is higher than that of the samples without in-situ annealing treatment, and the working voltage is also reduced.
The three groups of in-situ annealing modes of example 1 and comparative example 1, example 2 and comparative example 2, and example 3 and comparative example 3 in table 1 are respectively compared, each comparative example only adjusts the time ratio of each stage for the example of the same in-situ annealing mode, but the photoelectric test effect of the adjusted comparative example is not as good as that of the corresponding example, when the time ratio of each stage or other process parameters are changed, incomplete annealing, insufficient breaking of Mg-H bonds, or secondary bonding and the like are caused because byproducts after H dissociation are not discharged in time, and finally the photoelectric effect of the sample is poor. Therefore, the time ratio of each stage in the in-situ annealing cycle of the invention needs to be specifically set based on the selection of different in-situ annealing setting modes, so that a better photoelectric effect can be obtained.
Different from the condition of the prior art, the epitaxial growth method for improving the deep ultraviolet LED hole activation efficiency provided by the invention has the advantages that the periodic annealing stage is set, the nitrogen flow or the cavity pressure is adjusted, the Mg activation efficiency is improved, byproducts generated after H dissociation can be promoted to be discharged out of a reaction cavity in time, secondary bonding of Mg and H is effectively prevented, and the luminous efficiency of a deep ultraviolet LED device is improved.
The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. An epitaxial growth method for improving hole activation efficiency of a deep ultraviolet LED, comprising the steps of:
s1, preparing a deep ultraviolet LED epitaxial wafer;
s2, carrying out in-situ annealing on the deep ultraviolet LED epitaxial wafer for a plurality of periods in a nitrogen atmosphere;
in the single in-situ annealing period of the step S2, any process parameter of the cavity pressure or the nitrogen flow changes in a trend of firstly decreasing and then increasing.
2. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED according to claim 1, wherein the S2 step comprises four stages performed successively in sequence: a first constant annealing stage, a descending stage, a second constant annealing stage and an ascending stage;
and 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.
3. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED according to claim 1, wherein in the step S2, the annealing temperature is 800 to 950 ℃ and the annealing time is 1 to 40000S.
4. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED according to claim 1, wherein in the step S2, the in-situ annealing is performed for a period of 1 to 10.
5. The epitaxial growth method for improving hole activation efficiency of a deep ultraviolet LED according to claim 2, wherein in the single in-situ annealing cycle of the S2 step, the nitrogen flow is constant, and the cavity pressure is changed with a trend of decreasing first and then increasing;
the cavity pressure of the first constant annealing stage is greater than the cavity pressure of the second constant annealing stage, the cavity pressure of the descending stage is linearly decreased from the cavity pressure of the first constant annealing stage to the cavity pressure of the second constant annealing stage, and the cavity pressure of the ascending stage is linearly increased from the cavity pressure of the second constant annealing stage to the cavity pressure of the first constant annealing stage.
6. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED's according to claim 5, wherein the first constant annealing phase, the falling phase, the second constant annealing phase and the rising phase have a time ratio of 1;
the cavity pressure in the first constant annealing stage is constant at 200-500 mbar, and the cavity pressure in the second constant annealing stage is constant at 50-190 mbar.
7. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED according to claim 2, characterized in that in the single in-situ annealing cycle of the step S2, the cavity pressure is constant, and the nitrogen flow rate is changed with a trend of decreasing first and then increasing;
the nitrogen flow rate of the first constant annealing stage is greater than the nitrogen flow rate of the second constant annealing stage, the nitrogen flow rate of the descending stage is linearly decreased from the nitrogen flow rate of the first constant annealing stage to the nitrogen flow rate of the second constant annealing stage, and the nitrogen flow rate of the ascending stage is linearly increased from the nitrogen flow rate of the second constant annealing stage to the nitrogen flow rate of the first constant annealing stage.
8. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED's according to claim 7, wherein the first constant annealing phase, the falling phase, the second constant annealing phase and the rising phase have a time ratio of 4;
the nitrogen flow rate of the first constant annealing stage is constant and is 50-70 slm, and the nitrogen flow rate of the second constant annealing stage is constant and is 30-45 slm.
9. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED of claim 2, wherein in the single in-situ annealing cycle of the step S2, the cavity pressure and the nitrogen flow rate are changed synchronously with the trend of decreasing and then increasing;
the cavity pressure of the first constant annealing stage is greater than the cavity 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 decreasing stage is linearly decreased from the chamber pressure of the first constant annealing stage to the chamber pressure of the second constant annealing stage, and simultaneously, the nitrogen flow rate of the decreasing stage is linearly decreased 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 ramp-up stage is linearly increased from the chamber pressure of the second constant annealing stage to the chamber pressure of the first constant annealing stage, and simultaneously, the nitrogen flow rate of the ramp-up stage is linearly increased from the nitrogen flow rate of the second constant annealing stage to the nitrogen flow rate of the first constant annealing stage.
10. The epitaxial growth method for improving hole activation efficiency of deep ultraviolet LED's according to claim 9, wherein the first constant annealing phase, the falling phase, the second constant annealing phase and the rising phase have a time ratio of 2;
the pressure of the cavity in the first constant annealing stage is constant at 200-500 mbar, and the flow of nitrogen is constant at 50-70 slm;
the cavity pressure in the second constant annealing stage is constant at 50-190 mbar, and the nitrogen flow is constant at 30-45 slm.
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