An AlGaN-based UVB epitaxial wafer structure and a preparation method thereof

Abstract

The present invention belongs to the technical field of ultraviolet LED chips, and particularly relates to an AlGaN-based UVB epitaxial wafer structure and a preparation method thereof. The preparation method includes the following steps: preparing an AlN buffer layer with a thickness of 5 nm to 30 nm on the surface of a sapphire substrate; placing the sapphire substrate with the prepared AlN buffer layer in an MOCVD to grow a structure layer; growing a 3D AlGaN layer; growing a 2D AlGaN layer; growing an AlGaN layer with a composition of 50% to 60%; growing an nAlGaN layer doped with Si; growing a multi-quantum well active layer; growing an EBL layer; growing a hole injection layer; and growing a hole supply layer. By reasonably setting the composition gradient of the last two pairs of quantum wells, the present invention realizes the growth of a quantum well with a fixed single component, reduces the spatial separation of the electron and hole wave functions, improves the efficiency of carrier radiative recombination, and increases the proportion of the effective band integral area and the total spectral integral area.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultraviolet LED chips, and particularly relates to an AlGaN-based UVB epitaxial wafer structure and a preparation method thereof. Background Art

[0002] In traditional AlGaN-based UVB epitaxial structures, AlGaN materials are grown on the substrate material of an AlN template. The AlN template is the substrate material for the epitaxial growth of AlGaN-based deep ultraviolet LEDs. The crystallization quality of the template directly determines the crystal quality of the upper AlGaN. A high-quality AlN template can effectively reduce the threading dislocation density (TDDs) of AlGaN, improve the radiative recombination efficiency of electrons and holes in the LED structure grown on this material, and improve the reliability and lifespan of the LED.

[0003] Growing AlGaN-based materials on the surface of the AlN template is heteroepitaxial growth, and there is a lattice mismatch between the two. The magnitude of the lattice mismatch is related to the difference in material composition. The greater the composition difference, the greater the lattice mismatch. The lattice constants of AlN are a = 0.3112 nm and c = 0.4982 nm, and the lattice constants of GaN are a = 0.31896 nm and c = 0.51855 nm. The lattice mismatch between AlN and GaN is 2.5%. According to Vegard's law, for an Al x Ga 1-x N ternary compound with an Al component x (0 ≤ x ≤ 1), in a fully relaxed state, its lattice constant is a AlxGa1-xN = x * a AlN + (1 - x) * GaN . Therefore, for a certain composition of Al x Ga 1-x N (x < 1), its lattice constant is greater than that of AlN, and the lattice mismatch between the two depends on the component x. The larger x is, the greater the lattice mismatch between Al x Ga 1-x N and AlN, and the morphology and crystal quality of the Al x Ga 1-x N grown on the surface of the AlN template are worse.

[0004] In a UVB structure with an emission wavelength of 294 nm to 300 nm, the composition of the quantum well is 30% to 39%. In order to reduce the lattice mismatch between the quantum well layer and the nAl x Ga 1-x N template, it is necessary to grow an nAl x Ga 1-x N layer with a lower composition. However, the nAl x Ga 1-xThe N layer will have a greater lattice mismatch with the AlN template. Therefore, during the preparation process of the UVB epitaxial structure, the preparation of the nAl x Ga 1-x N template is relatively difficult. There is a large lattice mismatch between the nAl x Ga 1-x N layer and the AlN template layer, which will cause a large number of hexagonal protrusions with a height of 100 nm to 180 nm on the surface of the epitaxial layer, thus affecting the surface roughness, and further affecting the flatness of the interface between the quantum well layer and the barrier layer, and widening the half-wave width of the quantum well emission spectrum. At the same time, the large lattice mismatch will lead to the multiplication of dislocations, increasing the dislocation density of the nAlGaN layer, and then extending the dislocation density into the quantum well layer, thereby reducing the internal quantum efficiency.

[0005] In the traditional process of the UVB epitaxial structure, generally 3 to 10 pairs of quantum barrier / quantum well structures are used, and they are all periodic repetitive structures. The growth conditions in the growth process are also periodic repetitive.

[0006] During the epitaxial growth process, the migration rate of Al atoms is relatively low. To increase the migration rate, a higher growth temperature is required. The growth temperature of the AlN template is 1130 - 1250 °C, which has high requirements for the high-temperature performance of the MOCVD equipment. At the same time, during the growth of AlN, the AlN thin film layer grown on the inner chamber, the upper cover, and the surface of the graphite disk will affect the growth temperature of the subsequent epitaxial layer, resulting in unstable epitaxial process growth and affecting the crystallization quality and morphology stability of the AlN template. Therefore, the yield of using a high-temperature MOCVD equipment to grow the AlN template is relatively low, and to improve the yield, it is necessary to clean the upper cover for each furnace to reduce the influence of the AlN thin film layer on the upper cover on temperature control. Therefore, using the AlN template as the substrate material in the traditional process has the disadvantages of high threshold, low yield, and high cost.

[0007] Using the AlN template as the substrate material to grow nAlGaN with a composition of 50% - 60% will, due to lattice mismatch, result in a relatively rough morphology and a high dislocation density of nAlGaN. To improve the morphology of nAlGaN and reduce the dislocation density of nAlGaN, generally a single-component Al x Ga 1-x N layer is used for transition or a superlattice insertion layer is used to control strain and block the expansion of dislocations. However, both of these methods have relatively high requirements for process regulation. For example, using an AlN / AlGaN superlattice layer requires increasing the composition difference between the AlN and AlGaN layers, which has relatively strict requirements for growth conditions and reduces the process repeatability. Although there are obvious effects, they only reduce the relaxation caused by lattice mismatch and the dislocation multiplication during the relaxation process through transition and stress regulation methods, and cannot fundamentally eliminate lattice mismatch.

[0008] In the traditional UVB epitaxial structure, the growth parameters of multiple pairs of quantum barriers / quantum wells in the active region are designed with periodic repetition and the growth conditions are also periodically repeated. However, the inventor found in the experiment that the thicknesses of the quantum wells measured by TEM after actual growth of the multiple quantum wells designed according to the repetitive conditions are not the same, and the components of the quantum wells measured by SIMS are not fixed components. This will result in a wider full width at half maximum of the actual emission spectrum and a lower ratio of the integrated intensity of the effective spectrum to the integrated intensity of all spectra.

[0009] The invention patent with the publication number CN103165777B provides an LED epitaxial wafer with an N-type insertion layer having a trapezoidal structure and a growth method thereof. Although it is mentioned in this solution that the N-type AlGaN insertion layer has a trapezoidal structure, the trapezoidal structure may cause uneven stress during the growth process, thereby affecting the crystal quality of the material and the reliability of the device.

[0010] The invention patent application with the publication number CN106920866A provides an epitaxial method for regulating the wavelength of an ultraviolet light-emitting diode epitaxial wafer. It is difficult to precisely control the carrier concentration in the undoped layer, and uneven carrier distribution easily occurs, which will result in uneven electric field and current distribution in the active region, making the light-emitting efficiency of the device inconsistent, affecting the uniformity and stability of light emission, and causing problems such as uneven display brightness in display applications. Summary of the Invention

[0011] Aiming at the disadvantages of high threshold, low yield and high cost in using an AlN template as the substrate material in the above traditional process, and the technical problem that the components of the quantum wells measured by SIMS in the traditional UVB epitaxial structure are not fixed components, the present invention provides an AlGaN-based UVB epitaxial wafer structure and a preparation method thereof.

[0012] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0013] A preparation method of an AlGaN-based UVB epitaxial wafer structure includes the following steps:

[0014] S1. Prepare an AlN buffer layer with a thickness of 5 nm to 30 nm on the surface of a sapphire substrate;

[0015] S2. Place the sapphire substrate with the AlN buffer layer prepared thereon in the MOCVD to grow the structural layer; S2.1. Grow a 300 nm - 400 nm 3D AlGaN layer on the AlN buffer layer; S2.2. Grow a 2D AlGaN layer on the 3D AlGaN layer; S2.3. Grow an AlGaN layer with an Al composition of 50% - 60% on the 2D AlGaN layer; S2.4. Grow an Si-doped n-AlGaN layer on the AlGaN layer; S2.5. Grow a multi-quantum well active layer on the Si-doped n-AlGaN layer; S2.6. Grow an EBL layer on the multi-quantum well active layer; S2.7. Grow a hole injection layer on the EBL layer; S2.8. Grow a hole supply layer on the hole injection layer.

[0016] The growth process of preparing a 5 nm - 30 nm AlN buffer layer on the surface of the sapphire substrate in S1 is as follows: the temperature is 550 °C - 700 °C, the sputtering power is 1000 W - 4000 W, the nitrogen flow rate is 80 sccm - 200 sccm, the oxygen flow rate is 0.5 sccm - 5 sccm, the argon flow rate is 0.1 sccm - 40 sccm, and the deposition time is 16 s - 100 s.

[0017] The growth process of growing a 300 nm - 400 nm 3D AlGaN layer in S2.1 is as follows: the temperature gradually changes from 950 °C to 1000 °C, the pressure is 20 torr - 35 torr, the TMAl flow rate is 120 μmol / min - 150 μmol / min, the TMGa flow rate gradually changes from 480 μmol / min - 600 μmol / min to 610 μmol / min - 720 μmol / min, the NH3 flow rate is 2000 sccm - 6000 sccm, the carrier gas is a mixed gas of H2 and N2, the H2 carrier gas flow rate is 15 L / min - 30 L / min, the N2 carrier gas flow rate is 15 L / min - 30 L / min, and the growth thickness is 300 nm - 400 nm.

[0018] The growth process of growing a 2D AlGaN layer in S2.2 is as follows: the temperature gradually changes from 1150 °C to 1200 °C, the pressure is 20 torr - 35 torr, the TMAl flow rate is 120 μmol / min - 150 μmol / min, the TMGa flow rate gradually changes from 600 μmol / min - 750 μmol / min to 760 μmol / min - 900 μmol / min, the NH3 flow rate is 200 sccm - 600 sccm, pure N2 carrier gas is introduced, the carrier gas flow rate is 30 L / min - 60 L / min, and the growth thickness is 200 nm - 300 nm;

[0019] The growth process of the AlGaN layer with an Al composition of 50% - 60% in S2.3 is as follows: the temperature gradually changes from 1200 °C to 1100 °C, the pressure is 20 torr - 35 torr, the flow rate of TMAl is 120 μmol / min - 150 μmol / min, the flow rate of TMGa gradually changes from 720 μmol / min - 900 μmol / min to 540 μmol / min - 675 μmol / min, the flow rate of NH3 is 200 sccm - 600 sccm, pure N2 carrier gas is introduced, the carrier gas flow rate is 30 L / min - 60 L / min, and the growth thickness is 450 nm - 550 nm.

[0020] The growth process of the Si-doped nAlGaN layer in S2.4 is as follows: the temperature is 1100 °C, the pressure is 20 torr - 35 torr, the flow rate of TMAl is 120 μmol / min - 150 μmol / min, the flow rate of TMGa is 540 - 675 μmol / min, the flow rate of NH3 is 200 sccm - 600 sccm, pure N2 carrier gas is introduced, the carrier gas flow rate is 30 L / min - 60 L / min, the growth thickness is 3500 nm - 4500 nm, and the doping concentration of SiH4 is 3E17 cm -3 ~5E18 cm -3 .

[0021] The growth process of the multi-quantum well active layer in S2.5 is as follows: the number of periods is 3 pairs to 5 pairs, the temperature is 1000 °C to 1050 °C, the pressure is 35 torr to 100 torr, the flow rate of TMAl is 80 μmol / min to 100 μmol / min, and the flow rate of TMGa is 53 μmol / min to 66 μmol / min; the Al composition of the barrier layer is 60% to 65%, the thickness is 10 nm to 20 nm. The third to the first quantum wells from the bottom are fixed-composition quantum wells. The quantum wells are in the positive direction perpendicular to the epitaxial growth direction, the temperature is 1100 °C, the pressure is 35 torr to 100 torr, the flow rate of TMAl is 40 μmol / min to 50 μmol / min, the flow rate of TMGa is 160 μmol / min to 200 μmol / min, the set Al composition of the well layer is 20% to 25%, the actual composition is 40% to 45%, and the thickness is 1.1 nm to 2 nm; for the two quantum well layers near the p side, the temperature is 1100 °C, the pressure is 35 torr to 100 torr, the flow rate of TMGa is 160 μmol / min to 200 μmol / min, the flow rate of TMAl gradually changes from 17.8 μmol / min to 22.3 μmol / min to 8.45 μmol / min to 10.5 μmol / min, the set Al composition of the well layer gradually changes from 10% to 5%, the actual composition is 30% to 39%, and the thickness is 1.1 nm to 2 nm.

[0022] The growth process of the EBL layer in S2.6 is as follows: the EBL layer adopts a multi-quantum well structure or a single-layer EBL. The number of periods of the multi-quantum well structure is 1 pair to 5 pairs, the Al composition of the barrier layer is 60% to 80%, the thickness is 6 nm to 20 nm, the Al composition of the well layer is 40% to 50%, and the thickness is 1.5 nm to 3.5 nm; the composition of the single-layer EBL is 60% to 80%, and the thickness is 30 nm to 70 nm.

[0023] The growth process of the hole injection layer in S2.7 is as follows: the hole injection layer is pAlGaN with a gradually changing composition, the Al composition gradually changes from 0.7 to 0.35, the thickness is 15 nm to 40 nm, and the Mg doping concentration is 1E19 cm -3 ~2E20 cm -3 。

[0024] The growth process of the hole supply layer in S2.8 is as follows: the hole supply layer is pGaN, the thickness is 1 nm to 10 nm, and the Mg doping concentration is 1E20 cm -3 ~2E21 cm -3 。

[0025] An AlGaN-based UVB epitaxial wafer structure includes a sapphire substrate, an AlN buffer layer, a 3D AlGaN layer, a 2D AlGaN layer, an AlGaN layer, an nAlGaN layer, a multi-quantum well active layer, an EBL layer, a hole injection layer, and a hole supply layer. The AlN buffer layer is grown on the sapphire substrate, the 3D AlGaN layer is grown on the AlN buffer layer, the 2D AlGaN layer is grown on the 3D AlGaN layer, the AlGaN layer is grown on the 2D AlGaN layer, the nAlGaN layer is grown on the AlGaN layer, the multi-quantum well active layer is grown on the nAlGaN layer, the EBL layer is grown on the multi-quantum well active layer, the hole injection layer is grown on the EBL layer, and the hole supply layer is grown on the hole injection layer.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. By reasonably using temperature gradient and the ratio change of TMAl and TMGa flow rates, the present invention realizes the two-step growth of AlGaN with a certain composition as a single alloy material with a fixed composition, eliminating the growth of the AlN template. This not only reduces the requirement for the high-temperature resistance performance of the equipment but also avoids the disadvantage of poor repeatability in the growth of the AlN template. At the same time, it also avoids the dislocation multiplication caused by the lattice mismatch between the AlN template and the subsequent AlGaN material, achieving high-quality growth of low-resistance AlGaN.

[0028] 2. By reasonably setting the composition gradient of the last two pairs of quantum wells, the present invention realizes the growth of a fixed single-component quantum well, reduces the spatial separation of the electron and hole wave functions, improves the efficiency of carrier radiation, and increases the proportion of the effective band integral area and the total spectral integral area.

[0029] 3. Using the nAlGaN template process and the composition-gradient quantum well growth process without the AlN template structure, the present invention prepares a UVB epitaxial structure with a flat interface, a low dislocation density, and a low QCSE effect, increasing the proportion of the effective spectrum for supplementing the VD3 light source, avoiding the use of a filter, and improving the light efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and those of ordinary skill in the art can also obtain other implementation drawings according to the provided drawings without creative efforts.

[0031] The structures, ratios, sizes, etc. shown in this specification are only used to match the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they do not have any substantial technical meaning. Any modification of the structure, change in the ratio relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0032] Figure 1 is a schematic structural diagram of the present invention;

[0033] Figure 2 is a growth process curve diagram of the present invention;

[0034] Figure 3 is a schematic diagram of the designed Al composition of the present invention;

[0035] Figure 4 is a schematic diagram of the actual Al composition of the present invention;

[0036] Figure 5 is the original process spectrum diagram;

[0037] Figure 6 is the process spectrum diagram of the present invention;

[0038] Figure 7 is the light maintenance rate diagram of the original process UVB epitaxial wafer for 168h;

[0039] Figure 8 is the light maintenance rate diagram of the process UVB epitaxial wafer of the present invention for 168h.

[0040] Among them: 1 is a sapphire substrate, 2 is an AlN buffer layer, 3 is a 3D AlGaN layer, 4 is a 2D AlGaN layer, 5 is an AlGaN layer, 6 is an nAlGaN layer, 7 is a multi-quantum well active layer, 8 is an EBL layer, 9 is a hole injection layer, and 10 is a hole supply layer. Detailed implementation manners

[0041] To make the purposes, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. These descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention; based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0042] The following will further describe in detail the specific embodiments of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0043] In the description of the present application, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations. Embodiment

[0044] A preparation method for an AlGaN-based UVB epitaxial wafer structure, as Figure 1-4 shown, includes the following steps:

[0045] Step 1: Prepare an AlN buffer layer 2 with a thickness of 5 nm to 30 nm on the surface of a 2-inch sapphire substrate 1. The magnetron sputtering growth process is as follows: the temperature is 550 °C to 700 °C, the sputtering power is 1000 W to 4000 W, the nitrogen flow rate is 80 sccm to 200 sccm, the oxygen flow rate is 0.5 sccm to 5 sccm, the argon flow rate is 0.1 sccm to 40 sccm, and the deposition time is 16 s to 100 s.

[0046] Step 2: Place the sapphire substrate 1 with the AlN buffer layer 2 prepared thereon in MOCVD to grow a structure layer:

[0047] Step 2.1: Grow a 3D AlGaN layer 3 with a thickness of 300 to 400 nm. The specific growth process at this stage is as follows: the temperature gradually changes from 950 °C to 1000 °C, the pressure is 20 torr to 35 torr, the TMAl flow rate is 120 μmol / min to 150 μmol / min, the TMGa flow rate gradually changes from 480 μmol / min to 600 μmol / min to 610 μmol / min to 720 μmol / min, the NH3 flow rate is 2000 sccm to 6000 sccm, the carrier gas is a mixed gas of H2 and N2, the H2 carrier gas flow rate is 15 L / min to 30 L / min, the N2 carrier gas flow rate is 15 L / min to 30 L / min, and the growth thickness is 300 nm to 400 nm.

[0048] Step 2.2: Grow the 2D AlGaN layer 4, with the temperature gradually changing from 1150 °C to 1200 °C, the pressure being 20 torr - 35 torr, the TMAl flow rate being 120 μmol / min - 150 μmol / min, the TMGa flow rate gradually changing from 600 μmol / min - 750 μmol / min to 760 μmol / min - 900 μmol / min, the NH3 flow rate being 200 sccm - 600 sccm, using pure N2 as the carrier gas with a carrier gas flow rate of 30 L / min - 60 L / min, and the growth thickness being 200 nm - 300 nm. This process ensures that the actual composition of the grown AlGaN layer 5 is a constant 50% - 60% by comprehensively using the processes of gradually increasing the temperature and gradually increasing the molar fraction of TMGa at a relatively high temperature. After increasing the temperature, the mobilities of both Al and Ga will increase, achieving a two-dimensional planar growth mode. However, the incorporation efficiency of Ga will decrease with the increase in temperature. By increasing the molar fraction of TMGa, it is ensured that the actual Al composition is consistent with that of the 3D AlGaN layer 3.

[0049] Step 2.3: Grow the AlGaN layer 5 on the 2D AlGaN layer 4 where island coalescence has been completed, with the temperature gradually changing from 1200 °C to 1100 °C, the pressure being 20 torr - 35 torr, the TMAl flow rate being 120 μmol / min - 150 μmol / min, the TMGa flow rate gradually changing from 720 μmol / min - 900 μmol / min to 540 μmol / min - 675 μmol / min, the NH3 flow rate being 200 sccm - 600 sccm, using pure N2 as the carrier gas with a carrier gas flow rate of 30 L / min - 60 L / min, and the growth thickness being 450 nm - 550 nm. This process ensures that the actual Al composition of the grown AlGaN layer 5 is a constant 50% - 60% by comprehensively using the processes of gradually decreasing the temperature and gradually decreasing the molar fraction of TMGa at a relatively high temperature.

[0050] Step 2.4: Homoepitaxially grow the Si-doped n-AlGaN layer 6 on the AlGaN layer 5 with an Al composition of 50% - 60% and a flat surface using fixed growth conditions. The temperature is 1100 °C, the pressure is 20 torr - 35 torr, the TMAl flow rate is 120 μmol / min - 150 μmol / min, the TMGa flow rate is 540 μmol / min - 675 μmol / min, the NH3 flow rate is 200 sccm - 600 sccm, using pure N2 as the carrier gas with a carrier gas flow rate of 30 L / min - 60 L / min, the growth thickness is 3500 nm - 4500 nm, and the SiH4 doping concentration is 3E17 cm -3 ~5E18 cm -3 。

[0051] Step 2.5: Grow the multi-quantum well active layer 7 with 3 to 5 periods, at a temperature of 1100 °C, a pressure of 35 torr to 100 torr, a TMAl flow rate of 80 μmol / min to 100 μmol / min, a TMGa flow rate of 53 μmol / min to 66 μmol / min, an Al composition in the barrier layer of 60% to 65%, a thickness of 10 nm to 20 nm. The third to the first quantum wells from the bottom are fixed-composition quantum wells, at a temperature of 1100 °C, a pressure of 35 torr to 100 torr, a TMAl flow rate of 40 μmol / min to 50 μmol / min, a TMGa flow rate of 160 μmol / min to 200 μmol / min, with the Al composition in the well layer set to 20% to 25% and the actual composition being 40% to 45%, and a thickness of 1.1 nm to 2 nm. For the two quantum well layers near the p side, at a temperature of 1100 °C, a pressure of 35 torr to 100 torr, a TMGa flow rate of 160 μmol / min to 200 μmol / min, the TMAl flow rate gradually changes from 17.8 μmol / min to 22.3 μmol / min to 8.45 μmol / min to 10.5 μmol / min, the Al composition in the well layer gradually changes from 10% to 5%, the actual composition is 30% to 39%, and the thickness is 1.1 nm to 2 nm.

[0052] Step 2.6: Grow the EBL layer 8. The EBL layer 8 can be a multi-quantum well structure with 1 to 5 periods, an Al composition in the barrier layer of 60% to 80%, a thickness of 6 nm to 20 nm, an Al composition in the well layer of 40% to 50%, and a thickness of 1.5 nm to 3.5 nm; or it can be a single-layer EBL with a composition of 60% to 80% and a thickness of 30 nm to 70 nm.

[0053] Step 2.7: Grow the hole injection layer 9, which is a pAlGaN with a gradually changing composition. The Al composition of the hole injection layer 9 gradually changes from 0.7 to 0.35, the thickness of the hole injection layer 9 is 15 nm to 40 nm, and the Mg doping concentration is 1E19 cm -3 ~2E20 cm -3 .

[0054] Step 2.8: Grow the hole supply layer 10, which is pGaN with a thickness of 1 nm to 10 nm and a Mg doping concentration of 1E20 cm -3 ~2E21 cm -3 . Example

[0055] An AlGaN-based UVB epitaxial wafer structure, as Figure 1As shown in the figure, it includes a sapphire substrate 1, an AlN buffer layer 2, a 3D AlGaN layer 3, a 2D AlGaN layer 4, an AlGaN layer 5, an nAlGaN layer 6, a multi-quantum well active layer 7, an EBL layer 8, a hole injection layer 9, and a hole supply layer 10. The AlN buffer layer 2 is grown on the sapphire substrate 1, the 3D AlGaN layer 3 is grown on the AlN buffer layer 2, the 2D AlGaN layer 4 is grown on the 3D AlGaN layer 3, the AlGaN layer 5 is grown on the 2D AlGaN layer 4, the nAlGaN layer 6 is grown on the AlGaN layer 5, the multi-quantum well active layer 7 is grown on the nAlGaN layer 6, the EBL layer 8 is grown on the multi-quantum well active layer 7, the hole injection layer 9 is grown on the EBL layer 8, and the hole supply layer 10 is grown on the hole injection layer 9.

[0056] For the UVB LED prepared by the above process, the peak emission wavelength of the LED is in the range of 295 nm to 299 nm. The original process UVB epitaxial wafer uses AlN as the template material to grow nAlGaN with a composition of 55%, and the quantum well setting condition is a UVB epitaxial wafer with 5 pairs of quantum wells repeated. The UVB epitaxial wafer of the process of the present invention uses nAlGaN with a composition of 55% prepared in Example 1 of the present invention, and the last two quantum wells in the quantum well are quantum wells with gradually decreasing composition, and other structures are the same as those of the original process UVB epitaxial wafer. The epitaxial wafers grown by the two processes are respectively made into 20 mil × 20 mil chips, and the spectra and light maintenance rates of the two chips are tested under the condition of 10 mA. The results are as follows:

[0057] 1) Comparison of the integral area ratio of 281 nm - 306 nm: From Figure 5 and Figure 6 it can be seen that after using the process of the present invention, the full width at half maximum is reduced from 14 nm to 11.8 nm, and the ratio of the integral area of the 281 nm - 306 nm band to the total spectral integral area is increased from 85.2% to 90.6%.

[0058] 2) Comparison of the light maintenance rate: From Figure 7 and Figure 8 it can be seen that after using the process of the present invention, the 168-hour light maintenance rate is increased from 91% - 93% of the original process to more than 100%.

[0059] Only the preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A preparation method of an AlGaN-based UVB epitaxial wafer structure, characterized in that It includes the following steps: S1. Prepare an AlN buffer layer (2) with a thickness of 5 nm to 30 nm on the surface of a sapphire substrate (1) at a temperature of 550 °C to 700 °C, a sputtering power of 1000 W to 4000 W, a nitrogen flow rate of 80 sccm to 200 sccm, an oxygen flow rate of 0.5 sccm to 5 sccm, an argon flow rate of 0.1 sccm to 40 sccm, and a deposition time of 16 s to 100 s; S2. Place the sapphire substrate (1) with the prepared AlN buffer layer (2) in MOCVD to grow a structure layer; S2.

1. Grow a 3D AlGaN layer (3) with a thickness of 300 nm to 400 nm on the AlN buffer layer (2), with the temperature gradually changing from 950 °C to 1000 °C, a pressure of 20 torr to 35 torr, a TMAl flow rate of 120 μmol / min to 150 μmol / min, a TMGa flow rate gradually changing from 480 μmol / min to 600 μmol / min to 610 μmol / min to 720 μmol / min, an NH3 flow rate of 2000 sccm to 6000 sccm, a carrier gas being a mixed gas of H2 and N2, an H2 carrier gas flow rate of 15 L / min to 30 L / min, an N2 carrier gas flow rate of 15 L / min to 30 L / min, and a growth thickness of 300 nm to 400 nm; S2.

2. Grow a 2D AlGaN layer (4) on the 3D AlGaN layer (3), with the temperature gradually changing from 1150 °C to 1200 °C, a pressure of 20 torr to 35 torr, a TMAl flow rate of 120 μmol / min to 150 μmol / min, a TMGa flow rate gradually changing from 600 μmol / min to 750 μmol / min to 760 μmol / min to 900 μmol / min, an NH3 flow rate of 200 sccm to 600 sccm, introducing pure N2 as the carrier gas, a carrier gas flow rate of 30 L / min to 60 L / min, and a growth thickness of 200 nm to 300 nm; S2.

3. Grow an AlGaN layer (5) with an Al composition of 50% to 60% on the 2D AlGaN layer (4), with the temperature gradually changing from 1200 °C to 1100 °C, a pressure of 20 torr to 35 torr, a TMAl flow rate of 120 μmol / min to 150 μmol / min, a TMGa flow rate gradually changing from 720 μmol / min to 900 μmol / min to 540 μmol / min to 675 μmol / min, an NH3 flow rate of 200 sccm to 600 sccm, introducing pure N2 as the carrier gas, a carrier gas flow rate of 30 L / min to 60 L / min, and a growth thickness of 450 nm to 550 nm; S2.

4. Grow a Si-doped nAlGaN layer (6) on the AlGaN layer (5); S2.

5. Grow a multi - quantum - well active layer (7) on the Si - doped nAlGaN layer (6). The number of periods is 5 pairs, the temperature is 1000 °C to 1050 °C, the pressure is 35 torr to 100 torr, the TMAl flow rate is 80 μmol / min to 100 μmol / min, and the TMGa flow rate is 53 μmol / min to 66 μmol / min. The Al composition of the barrier layer is 60% to 65%, and the thickness is 10 nm to 20 nm. Prepare the third - last to the first quantum wells as fixed - composition quantum wells. The quantum wells are positive along the direction perpendicular to the epitaxial growth direction, the temperature is 1100 °C, the pressure is 35 torr to 100 torr, the TMAl flow rate is 40 μmol / min to 50 μmol / min, and the TMGa flow rate is 160 μmol / min to 200 μmol / min. The Al composition set for the well layer is 20% to 25%, the actual composition is 40% to 45%, and the thickness is 1.1 nm to 2 nm. Prepare the two quantum - well layers near the p - side. The temperature is 1100 °C, the pressure is 35 torr to 100 torr, the TMGa flow rate is 160 μmol / min to 200 μmol / min, the TMAl flow rate gradually changes from 17.8 μmol / min to 22.3 μmol / min to 8.45 μmol / min to 10.5 μmol / min, the Al composition set for the well layer gradually changes from 10% to 5%, the actual composition is 30% to 39%, and the thickness is 1.1 nm to 2 nm. S2.

6. Grow an EBL layer (8) on the multi - quantum - well active layer (7); S2.

7. Grow a hole - injection layer (9) on the EBL layer (8); S2.

8. Grow a hole - supply layer (10) on the hole - injection layer (9).

2. The preparation method of an AlGaN-based UVB epitaxial wafer structure according to claim 1, wherein, The growth process of the Si-doped nAlGaN layer (6) in S2.4 is as follows: the temperature is 1100 °C, the pressure is 20 torr to 35 torr, the flow rate of TMAl is 120 μmol / min to 150 μmol / min, the flow rate of TMGa is 540 to 675 μmol / min, the flow rate of NH3 is 200 sccm to 600 sccm, pure N2 carrier gas is introduced, the flow rate of the carrier gas is 30 L / min to 60 L / min, the growth thickness is 3500 nm to 4500 nm, and the doping concentration of SiH4 is 3E17 cm -3 ~5E18 cm -3 .

3. The preparation method of an AlGaN-based UVB epitaxial wafer structure according to claim 1, characterized in that, The growth process of growing the EBL layer (8) in S2.6 is as follows: The EBL layer (8) adopts a multi - quantum - well structure or a single - layer EBL. The number of periods of the multi - quantum - well structure is 1 pair to 5 pairs, the Al composition of the barrier layer is 60% to 80%, the thickness is 6 nm to 20 nm, the Al composition of the well layer is 40% to 50%, and the thickness is 1.5 nm to 3.5 nm. The composition of the single - layer EBL is 60% to 80%, and the thickness is 30 nm to 70 nm.

4. The preparation method of an AlGaN-based UVB epitaxial wafer structure according to claim 1, characterized in that, The growth process of the hole injection layer (9) in S2.7 is as follows: The hole injection layer (9) is a pAlGaN with a gradually changing composition, the Al component gradually changes from 0.7 to 0.35, the thickness is 15 nm to 40 nm, and the Mg doping concentration is 1E19 cm -3 ~2E20 cm -3 .

5. The preparation method of an AlGaN-based UVB epitaxial wafer structure according to claim 1, characterized in that, The growth process of the hole supply layer (10) in S2.8 is as follows: The hole supply layer (10) is pGaN, with a thickness of 1 nm to 10 nm and an Mg doping concentration of 1E20 cm -3 ~2E21 cm -3 .

6. An AlGaN-based UVB epitaxial wafer structure prepared by the preparation method of an AlGaN-based UVB epitaxial wafer structure according to any one of claims 1-5, characterized in that: It includes a sapphire substrate (1), an AlN buffer layer (2), a 3D AlGaN layer (3), a 2D AlGaN layer (4), an AlGaN layer (5), an nAlGaN layer (6), a multi-quantum well active layer (7), an EBL layer (8), a hole injection layer (9) and a hole supply layer (10). The AlN buffer layer (2) is grown on the sapphire substrate (1), the 3D AlGaN layer (3) is grown on the AlN buffer layer (2), the 2D AlGaN layer (4) is grown on the 3D AlGaN layer (3), the AlGaN layer (5) is grown on the 2D AlGaN layer (4), the nAlGaN layer (6) is grown on the AlGaN layer (5), the multi-quantum well active layer (7) is grown on the nAlGaN layer (6), the EBL layer (8) is grown on the multi-quantum well active layer (7), the hole injection layer (9) is grown on the EBL layer (8), and the hole supply layer (10) is grown on the hole injection layer (9).

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