UVB epitaxial wafer and preparation method thereof
By employing a multilayer stress relief and transition layer structure in the UVB LED epitaxial wafer, the problems of lattice mismatch and crystal quality were solved, improving the light maintenance rate and LED lifespan, and optimizing the phototherapy effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ADVANCED ULTRAVIOLET OPTOELECTRONICS CO LTD
- Filing Date
- 2024-11-05
- Publication Date
- 2026-05-08
AI Technical Summary
Existing UVB LED epitaxial wafers have problems with lattice mismatch and crystal quality, which lead to dislocation extension and broadening of the emission spectrum half-width, affecting the phototherapy effect and LED lifespan.
The structure employs a multilayer stress relief and transition layer, including multiple thin layers with gradually increasing composition. By gradually reducing the composition of the AlN template layer, dislocation generation is reduced, lattice quality and flatness are improved, and the half-width of the quantum well emission spectrum is reduced.
It improves the light maintenance rate and crystal quality of UVB LEDs, extends the lifespan of LEDs, and optimizes the phototherapy effect.
Smart Images
Figure CN122002972A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of ultraviolet LED epitaxial wafer fabrication, and more particularly to a UVB epitaxial wafer and its preparation method. Background Technology
[0002] In the field of medical technology, UVB phototherapy utilizes UVB light in the 280-315nm band to treat various skin diseases, such as psoriasis, eczema, pruritus, vitiligo, lichen planus, and granulomatosis. Currently, there are three main types of UVB phototherapy for skin diseases: (1) Broadband UVB: Treatment using UVB rays of 280-315nm. Wavelengths below 300nm can cause erythema or severe burning and increase the risk of skin cancer; (2) Narrowband UVB: Treatment using 311nm UVB with a narrower and stronger wavelength. This is the most commonly used phototherapy today. Narrowband UVB is generated by special fluorescent tubes designed to produce very narrow wavelength UVB light. 311nm has been proven to be very effective and safe in suppressing skin inflammation. It is now the most widely used form of phototherapy; (3) 308nm excimer laser: Treatment using 308nm excimer light to effectively target affected skin without overexposing other areas. The treatment effect is better than other traditional phototherapy methods.
[0003] Fluorescent tubes produce UVB spectra with a narrow half-width at half-maximum (HWHM) (<5nm), but their irradiance is low, resulting in a slower onset of action and longer treatment courses for skin diseases. They also have a larger light source size, require high-voltage drive, and have a lifespan of only 1000-3000 hours. 308nm excimer lasers produce UVB spectra with a narrow HWHM (<5nm) and high irradiance, leading to faster onset of action for skin diseases. However, they also require high-voltage drive and have a short lifespan of only 200-600 hours. UVB LEDs produce spectra with a larger HWHM, generally between 12-15nm, with a typical HWHM of around 13.5nm. UVB irradiance can be precisely adjusted by regulating the current. UVB LEDs are also smaller, allowing for the creation of portable phototherapy devices. They have lower driving voltages, with a single LED driving voltage of 5-7V. Their lifespan is longer, exceeding 10,000 hours. Therefore, a bandpass filter is added at the front end of UVB LEDs during use, which results in approximately a 40% loss of UVB light.
[0004] Aluminum nitride (ANH) templates are the substrate materials for the epitaxial growth of aluminum gallium nitride (AlGaN)-based deep ultraviolet (DEUV) LEDs. The crystal quality of the template directly determines the crystal quality of the upper AlGaN layer. Growing AlGaN-based materials on the AlN template surface is a heterogeneous epitaxial growth process, resulting in a lattice mismatch between the two materials. The magnitude of this lattice mismatch is related to the difference in material composition; the greater the compositional difference, the greater the lattice mismatch. Therefore, for a given AlGaN composition... x Ga1-x N (x < 1) has a lattice constant greater than AlN, and the lattice mismatch between the two depends on the composition x; the larger x is, the greater the lattice mismatch between AlN and AlN. x Ga 1-x The greater the lattice mismatch between N and AlN, the more Al will grow on the AlN template surface. x Ga 1-x The worse the morphology and crystal quality of N, the worse it is.
[0005] Currently, there are two commonly used methods for adjusting stress. One is to grow a transition layer with gradually decreasing composition, achieving a transition in lattice constant through compositional gradient. However, this method uses a single-component Al. x Ga 1-x The transition through the N-layer cannot reduce the AlN-layer and lower component nAl. x Ga 1-x Lattice mismatch between N layers will extend dislocations into the quantum well layer, thereby reducing nonradiative recombination efficiency; at the same time, the AlN template layer with a small lattice constant will affect the nAl layer with a larger lattice constant. x Ga 1-x The N-layer generates significant compressive stress, thereby broadening the half-width of the quantum well's emission spectrum. Another approach is to grow an AlN / AlGaN superlattice layer between the AlN template and the n-type AlGaN. This method is more common, filtering dislocations through the superlattice while simultaneously releasing stress. However, the nAlGaN layer in the UVB structure has a lower composition and a greater mismatch with AlN. Using an AlN / AlGaN superlattice layer requires increasing the compositional difference between the AlN and AlGaN layers, which places stringent requirements on growth conditions and reduces the repeatability of the process. Summary of the Invention
[0006] To address the problems existing in the prior art, the present invention provides a UVB epitaxial wafer and its preparation method.
[0007] This invention provides a UVB epitaxial wafer, comprising: a substrate and a buffer layer on a first surface of the substrate; an AlN layer located on the buffer layer; and an Al layer with composition x. x Ga 1-xN layers, where 0.8 ≤ x ≤ 0.9; a superlattice layer comprising a stress relief layer and a transition layer, the stress relief layer comprising a first stress relief layer, a second stress relief layer and a third stress relief layer, each stress relief layer comprising several periods, each period having a thickness ranging from 5 to 10 nm; an electrode contact layer; a multi-quantum well active layer, the multi-quantum well active layer having an L-shaped structure comprising a first part and a second part, wherein the thickness of the first part is greater than the thickness of the second part; an electron blocking layer, a hole injection layer and a hole supply layer stacked sequentially, the electron blocking layer, the hole injection layer and the hole supply layer covering the first part of the multi-quantum well active layer; a first electrode layer located on the second part of the multi-quantum well active layer; and a second electrode layer located on the hole supply layer.
[0008] Optionally, the transition layer includes a first transition layer and a second transition layer, wherein the first transition layer is located between the first stress relief layer and the second stress relief layer, and the second transition layer is located between the second stress relief layer and the third stress relief layer.
[0009] Optionally, the material of the first transition layer includes Al with a composition of x-0.1. x-0.1 Ga 1.1-x N, the material of the second transition layer comprises Al with a composition of x-0.2. x-0.2 Ga 1.2-x N.
[0010] Optionally, the first stress relief layer includes n cycles, each cycle including 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first segment has a composition of x + 0.005*(n-1) - 0.2, the second segment has a composition of x + 0.0025n - 0.1525, the third segment has a composition of x - 0.1, the fourth segment has a composition of x - 0.0025n - 0.0475, and the fifth segment has a composition of x - 0.005n + 0.005.
[0011] Optionally, the first stress relief layer is a composition gradient layer comprising n periods, each period having a thickness ranging from 5 to 10 nm, wherein in the nth period, the composition gradually changes from x+0.005*(n-1)-0.2 to x-0.005n+0.005.
[0012] Optionally, the second stress relief layer includes n cycles, each cycle including 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first segment has a composition of x + 0.005*(n-1) - 0.3, the second segment has a composition of x + 0.0025n - 0.2525, the third segment has a composition of x - 0.2, the fourth segment has a composition of x - 0.0025n - 0.1475, and the fifth segment has a composition of x - 0.005n - 0.095.
[0013] Optionally, the second stress relief layer is a composition gradient layer comprising n periods, each period having a thickness ranging from 5 to 10 nm. In the nth period, the composition gradually changes from x+0.005*(n-1)-0.3 to x-0.005n-0.095.
[0014] Optionally, the third stress relief layer comprises n cycles, each cycle comprising 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first segment has a composition of x + 0.005*(n-1) - 0.4, the second segment has a composition of x + 0.0025n - 0.3525, the third segment has a composition of x - 0.3, the fourth segment has a composition of x - 0.0025n - 0.2475, and the fifth segment has a composition of x - 0.005n - 0.195.
[0015] Optionally, the third stress relief layer is a composition gradient layer comprising n periods, with each period having a thickness ranging from 5 to 10 nm. In the nth period, the composition gradually changes from x+0.005*(n-1)-0.4 to x-0.005n-0.195.
[0016] Optionally, the electrode contact layer comprises nAl with a composition of x-0.3. x-0.3 Ga 1.3-x N.
[0017] Optionally, the component x is Al x Ga 1-x The thickness of the N layer ranges from 50 to 200 nm, the thickness of the first transition layer ranges from 200 to 400 nm, the thickness of the second transition layer ranges from 200 to 400 nm, and the thickness of the electrode contact layer ranges from 200 to 1000 nm.
[0018] Optionally, the first electrode layer material includes at least one of chromium, titanium, aluminum, nickel, and gold, and the second electrode layer material includes at least one of nickel, rhodium, and titanium.
[0019] The present invention also provides a method for preparing a UVB epitaxial wafer, comprising the steps of: providing a substrate and forming a buffer layer on one side of a first surface of the substrate; forming an AlN layer on the surface of the buffer layer; and forming an Al layer with composition x on the AlN layer. x Ga 1-x N layers, where 0.8 ≤ x ≤ 0.9; in the Al x Ga 1-x A first stress-relief layer is formed on the surface of layer N, the first stress-relief layer comprising several periods, each period having a thickness ranging from 5 to 10 nm; a first transition layer is formed on the surface of the first stress-relief layer, the first transition layer being Al.x-0.1 Ga 1.1-x N; A second stress-relief layer is formed on the surface of the first transition layer, the second stress-relief layer comprising several periods, each period having a thickness ranging from 5 to 10 nm; A second transition layer is formed on the surface of the second stress-relief layer, the second transition layer being Al. x-0.2 Ga 1.2-x N; A third stress-relief layer is formed on the surface of the second transition layer, the third stress-relief layer comprising several periods, each period having a thickness ranging from 5 to 10 nm; an electrode contact layer is formed on the surface of the third stress-relief layer, the electrode contact layer being nAl x-0.3 Ga 1.3-x N; A multi-quantum-well active layer is formed on the electrode contact layer; An electron blocking layer, a hole injection layer, and a hole supply layer are sequentially formed on the multi-quantum-well active layer; Parts of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum-well active layer are etched until the electrode contact layer is exposed, and a mesa is formed on the electrode contact layer; A first electrode layer is formed on the mesa of the electrode contact layer; A second electrode layer is formed on the hole supply layer.
[0020] Optionally, forming a buffer layer on one side of the first surface of the substrate includes the step of: forming the buffer layer by a magnetron sputtering growth process, wherein the magnetron sputtering growth process conditions include: a temperature range of 550–700°C, a sputtering power range of 1000–4000W, a nitrogen flow rate range of 80–200 sccm, an oxygen flow rate range of 0.5–5 sccm, an argon flow rate range of 0.1–40 sccm, and a deposition time range of 16 s–100 s.
[0021] Optionally, forming an AlN layer on the surface of the buffer layer includes the steps of: forming an AlN 3D layer on the buffer layer using a vapor phase epitaxial growth process; and forming an AlN 2D layer on the buffer layer using a vapor phase epitaxial growth process.
[0022] Optionally, the etching of a portion of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum well active layer includes the step of: etching a portion of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum well active layer using an ICP etching process.
[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:
[0024] This invention provides a UVB epitaxial wafer and its preparation method. By repeatedly growing thin layers with gradually increasing composition, the Al composition is reduced while maintaining a constant lattice constant. Through repeated application of this principle, the AlN template layer is gradually reduced to an even lower Al composition. x Ga 1-xN, and reduce the probability of dislocation generation during this process, thereby improving nAl x Ga 1-x Improving the crystal quality of the N-layer and enhancing surface smoothness reduces the half-width of the quantum well's emission spectrum, thereby increasing the LED light maintenance rate. Attached Figure Description
[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0026] Figure 1 This is a schematic diagram of the structure of a UVB epitaxial wafer according to an embodiment of the present disclosure;
[0027] Figure 2 This is a schematic flowchart of a method for preparing a UVB epitaxial wafer according to an embodiment of the present disclosure;
[0028] Figure 3 This is a graph showing the variation of different epitaxial layer compositions with thickness in the first embodiment of this disclosure;
[0029] Figure 4 This is a graph showing the variation trend of different epitaxial layer compositions with thickness in the second embodiment of this disclosure.
[0030] Figure 5 Microscopic images of UVB epitaxial wafers grown using a single-component transition layer in existing technologies;
[0031] Figure 6 A microscope image of the UVB epitaxial wafer according to the first embodiment of this disclosure;
[0032] Figure 7 A microscope image of the UVB epitaxial wafer according to the second embodiment of this disclosure;
[0033] Figure 8 A comparative schematic diagram of the emission spectra of three types of LED chips prepared using existing technology and the first and second embodiments of this disclosure, respectively.
[0034] Figure 9 This is a schematic diagram comparing the light maintenance rates of three types of LED chips prepared using existing technology and the first and second embodiments of this disclosure. Detailed Implementation
[0035] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.
[0036] In this invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower parts of the device in its normal operating state, while "inner" and "outer" refer to the parts relative to the outline of the device. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Since this invention pertains to electrical devices, connection and interconnection both refer to conductive interconnections. Because the accompanying drawings describe the same device, the same reference numerals denote the same components.
[0037] Currently, there are two common methods for adjusting stress in the fabrication of ultraviolet LED epitaxial wafers. One method is to grow a transition layer with gradually decreasing composition, achieving a transition in lattice constant through compositional gradient. However, this method is limited when using a single-component Al. x Ga 1-x The transition through the N-layer cannot reduce the AlN-layer and lower component nAl. x Ga 1-x Lattice mismatch between N layers will extend dislocations into the quantum well layer, thereby reducing nonradiative recombination efficiency; at the same time, the AlN template layer with a small lattice constant will affect the nAl layer with a larger lattice constant. x Ga 1- x The N-layer generates significant compressive stress, thereby broadening the half-width of the quantum well's emission spectrum. Another approach is to grow an AlN / AlGaN superlattice layer between the AlN template and the n-type AlGaN. This method is more common, filtering dislocations through the superlattice while simultaneously releasing stress. However, the nAlGaN layer in the UVB structure has a lower composition and a greater mismatch with AlN. Using an AlN / AlGaN superlattice layer requires increasing the compositional difference between the AlN and AlGaN layers, which places stringent requirements on growth conditions and reduces the repeatability of the process.
[0038] Therefore, this disclosure provides a UVB epitaxial wafer and its preparation method, which can effectively solve the above problems and improve the LED light maintenance rate.
[0039] This disclosure provides a UVB epitaxial wafer, comprising: a substrate and a buffer layer on a first surface of the substrate; an AlN layer located on the buffer layer; and an AlN layer with composition x. x Ga1-x N layers, where 0.8 ≤ x ≤ 0.9; a superlattice layer comprising a stress relief layer and a transition layer, the stress relief layer comprising a first stress relief layer, a second stress relief layer and a third stress relief layer, each stress relief layer comprising several periods, each period having a thickness ranging from 5 to 10 nm; an electrode contact layer; a multi-quantum well active layer, the multi-quantum well active layer having an L-shaped structure comprising a first part and a second part, wherein the thickness of the first part is greater than the thickness of the second part; an electron blocking layer, a hole injection layer and a hole supply layer stacked sequentially, the electron blocking layer, the hole injection layer and the hole supply layer covering the first part of the multi-quantum well active layer; a first electrode layer located on the second part of the multi-quantum well active layer; and a second electrode layer located on the hole supply layer.
[0040] Figure 1 A schematic diagram of the structure of a UVB epitaxial wafer according to an embodiment of the present disclosure is shown. Figure 2 A schematic flowchart illustrating a method for preparing a UVB epitaxial wafer according to an embodiment of this disclosure is shown. Specific examples of the invention will be further described in detail below with reference to the accompanying drawings. Note that substances not specifically listed in the embodiments are optional and can be any commercially available substance that achieves the corresponding function.
[0041] Combination Figure 1 and Figure 2 The method for preparing the UVB epitaxial wafer includes the following steps:
[0042] S1: Provide a substrate and form a buffer layer on one side of the first surface of the substrate.
[0043] In this embodiment of the disclosure, the substrate 10 is made of sapphire.
[0044] A buffer layer 20 of 5–30 nm was prepared on the surface of a 2-inch sapphire planar substrate 10 by magnetron sputtering. The magnetron sputtering growth conditions were as follows: temperature range of 550–700 °C, sputtering power of 1000–4000 W, nitrogen flow rate range of 80–200 sccm, oxygen flow rate range of 0.5–5 sccm, argon flow rate range of 0.1–40 sccm, and deposition time of 16–100 s.
[0045] S2: An AlN layer is formed on the surface of the buffer layer.
[0046] In this embodiment of the disclosure, an AlN layer 30 of 2-5 μm is grown. The step of forming the AlN layer 30 on the surface of the buffer layer 20 includes: forming an AlN 3D layer on the buffer layer using a vapor phase epitaxial growth process; and forming an AlN 2D layer on the buffer layer using a vapor phase epitaxial growth process.
[0047] Specifically, firstly, an AlN 3D layer is grown on the surface of buffer layer 20. The specific growth process is as follows: temperature 800–1000℃, pressure 20–35 torr, TMAl flow rate 240–300 μmol / min, NH3 flow rate 2000–6000 sccm, pure H2 carrier gas, carrier gas flow rate 30–60 L / min, and growth thickness 150–500 nm. Next, an AlN 2D layer is grown. The specific growth process is as follows: temperature 1100–1350℃, pressure 20–35 torr, TMAl flow rate 240–300 μmol / min, NH3 flow rate 100–300 sccm, pure H2 carrier gas, carrier gas flow rate 30–60 L / min, and growth thickness 1850–4500 nm.
[0048] S3: Forming an Al layer with composition x on top of the AlN layer. x Ga 1-x N layers, where 0.8≤x≤0.9.
[0049] In this embodiment of the disclosure, Al with a thickness of 50-200 nm and composition x is grown on AlN layer 30 by magnetron sputtering. x Ga 1-x N layers, 40, where 0.8 ≤ x ≤ 0.9. For example, in one specific embodiment, Al with a thickness of 50–200 nm and a composition of 0.8 is grown. 0.8 Ga 0.2 Nth floor, 40.
[0050] S4: In the Al x Ga 1-x A first stress relief layer is formed on the surface of the N layer. The first stress relief layer contains several periods, each with a thickness ranging from 5 to 10 nm.
[0051] In one embodiment of this disclosure, the first stress relief layer includes n periods, each period including 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth period, the first segment has a composition of x + 0.005*(n-1) - 0.2, the second segment has a composition of x + 0.0025n - 0.1525, the third segment has a composition of x - 0.1, the fourth segment has a composition of x - 0.0025n - 0.0475, and the fifth segment has a composition of x - 0.005n + 0.005.
[0052] Specifically, for example, in the first embodiment of this disclosure, in Al 0.8 Ga 0.2A first stress-relief layer 510 with a thickness of 100–200 nm is grown on the surface of layer N40 to reduce composition. The first stress-relief layer 510 comprises 20 cycles, each cycle containing 5 thin layers, each thin layer being 1–2 nm thick. Figure 3 As shown, the first component of the first cycle is 0.6, the second component is 0.65, the third component is 0.7, the fourth component is 0.75, and the fifth component is 0.8. Similarly, the first component of the tenth cycle is 0.645, the second component is 0.6725, the third component is 0.7, the fourth component is 0.7275, and the fifth component is 0.755. Likewise, the first component of the twentieth cycle is 0.695, the second component is 0.6975, the third component is 0.7, the fourth component is 0.7025, and the fifth component is 0.705.
[0053] In another embodiment of this disclosure, the first stress relief layer 510 is a component gradient layer comprising n periods, each period having a thickness ranging from 5 to 10 nm, wherein in the nth period, the component gradually changes from x+0.005*(n-1)-0.2 to x-0.005n+0.005.
[0054] Specifically, for example, in the second embodiment of this disclosure, in Al 0.8 Ga 0.2 A first stress-relief layer 510 with a thickness of 100–200 nm is grown on the surface of layer N40 to reduce composition. The first stress-relief layer 510 comprises 20 cycles of composition-gradient layers, each cycle having a thickness of 5–10 nm. For example… Figure 4 As shown, the thickness of the first period is 5–10 nm, and the composition gradually changes from 0.6 to 0.8. Similarly, the thickness of the 10th period is 5–10 nm, and the composition gradually changes from 0.645 to 0.755. And so on, the thickness of the 20th period is 5–10 nm, and the composition gradually changes from 0.695 to 0.705.
[0055] In some embodiments, a first stress relief layer 510 comprising a component gradient layer of 20 cycles is prepared. The growth process parameters for the component gradient layer can be: temperature 1000-1100℃, NH3 flow rate 8000-24000 sccm, pure H2 carrier gas with a flow rate of 30-60 L / min, and a total amount of Group III MO source of 300-600 μmol / min. During the component gradient process, the total amount of Group III MO source remains constant, and the flow rate of TMAl gradually changes from the flow rate of the corresponding initial component to the flow rate of the final component. For example, if the component gradually changes from 0.6 to 0.8, then the flow rate of TMAl gradually changes from the total amount of MO source * 0.6 to the total amount of MO source * 0.8, and the growth rate is 0.5-1 μm / h.
[0056] S5: A first transition layer is formed on the surface of the first stress relief layer, wherein the first transition layer is Al. x-0.1 Ga 1.1- x N.
[0057] In this embodiment, a first transition layer 610 with a thickness of 200–400 nm is grown on the first stress relief layer 510. The material of the first transition layer 610 includes Al with a composition of x–0.1. x-0.1 Ga 1.1-x N. For example, Al with a growth thickness of 200–400 nm and a composition of 0.7. 0.7 Ga 0.3 N serves as the first transition layer 610.
[0058] S6: A second stress relief layer is formed on the surface of the first transition layer. The second stress relief layer contains several periods, and the thickness of each period ranges from 5 to 10 nm.
[0059] In one embodiment of this disclosure, the second stress relief layer 520 includes n periods, each period including 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth period, the first thin layer has a composition of x + 0.005*(n-1) - 0.3, the second thin layer has a composition of x + 0.0025n - 0.2525, the third thin layer has a composition of x - 0.2, the fourth thin layer has a composition of x - 0.0025n - 0.1475, and the fifth thin layer has a composition of x - 0.005n - 0.095.
[0060] Specifically, for example, in the first embodiment of this disclosure, a second stress relief layer 520 with a thickness of 100-200 nm is grown on the surface of the first transition layer 610 to reduce composition. The second stress relief layer 520 comprises 20 cycles, each cycle comprising 5 thin layers, each thin layer having a thickness of 1-2 nm. Figure 3As shown, the first component of the first cycle is 0.5, the second component is 0.55, the third component is 0.6, the fourth component is 0.65, and the fifth component is 0.7. Similarly, the first component of the tenth cycle is 0.545, the second component is 0.5725, the third component is 0.6, the fourth component is 0.6275, and the fifth component is 0.655. Likewise, the first component of the twentieth cycle is 0.595, the second component is 0.5975, the third component is 0.6, the fourth component is 0.6025, and the fifth component is 0.605.
[0061] In another embodiment of this disclosure, the second stress relief layer 520 is a composition-gradient layer comprising n periods, each period having a thickness ranging from 5 to 10 nm. Specifically, in the nth period, the composition gradually changes from x + 0.005*(n-1) - 0.3 to x - 0.005n - 0.095.
[0062] Specifically, for example, in the second embodiment of this disclosure, a second stress-relief layer 520 with a thickness of 100-200 nm is grown on the surface of the first transition layer 610 to reduce composition. The second stress-relief layer 520 is a composition-gradient layer comprising 20 cycles, each cycle having a thickness of 5-10 nm. Figure 4 As shown, the thickness of the first period is 5–10 nm, and the composition gradually changes from 0.5 to 0.7. Similarly, the thickness of the 10th period is 5–10 nm, and the composition gradually changes from 0.545 to 0.655. And so on, the thickness of the 20th period is 5–10 nm, and the composition gradually changes from 0.595 to 0.605.
[0063] In some embodiments, the growth process parameters for preparing the second stress relief layer 520 comprising a component gradient layer with 20 cycles can be as follows: temperature 1000-1100℃, NH3 flow rate 8000-24000 sccm, pure H2 carrier gas with a flow rate of 30-60 L / min, total amount of Group III MO source 300-600 μmol / min, during the component gradient process, the total amount of Group III MO source remains constant, and the flow rate of TMAl gradually changes from the flow rate of the corresponding starting component to the flow rate of the ending component. For example, if the component gradually changes from 0.5 to 0.7, then the flow rate of TMAl gradually changes from the total amount of MO source * 0.5 to the total amount of MO source * 0.7, and the growth rate is 0.5-1 μm / h.
[0064] S7: A second transition layer is formed on the surface of the second stress-relieving layer, wherein the second transition layer is Al. x-0.2 Ga1.2- x N.
[0065] In this embodiment, a second transition layer 620 with a thickness of 200–400 nm is grown on the second stress relief layer 520. The material of the second transition layer 620 includes Al with a composition of x–0.2. x-0.2 Ga 1.2-x N. For example, Al with a growth thickness of 200–400 nm and a composition of 0.6. 0.6 Ga 0.4 N serves as the second transition layer 620.
[0066] S8: A third stress relief layer is formed on the surface of the second transition layer, the third stress relief layer comprising several periods, each period having a thickness ranging from 5 to 10 nm.
[0067] In one embodiment of this disclosure, the third stress relief layer includes n cycles, each cycle including 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first segment has a composition of x + 0.005*(n-1) - 0.4, the second segment has a composition of x + 0.0025n - 0.3525, the third segment has a composition of x - 0.3, the fourth segment has a composition of x - 0.0025n - 0.2475, and the fifth segment has a composition of x - 0.005n - 0.195.
[0068] For example, in the first embodiment of this disclosure, a third stress-relieving layer 530 with a thickness of 100-200 nm that can reduce composition is grown. The third stress-relieving layer 530 comprises 20 cycles, each cycle comprising 5 thin layers, each thin layer having a thickness of 1-2 nm. Figure 3 As shown, the first component of the first cycle is 0.4, the second component is 0.45, the third component is 0.5, the fourth component is 0.55, and the fifth component is 0.6. Similarly, the first component of the tenth cycle is 0.445, the second component is 0.4725, the third component is 0.5, the fourth component is 0.5275, and the fifth component is 0.555. Likewise, the first component of the twentieth cycle is 0.495, the second component is 0.4975, the third component is 0.5, the fourth component is 0.5025, and the fifth component is 0.505.
[0069] In another embodiment of this disclosure, the third stress relief layer is a composition gradient layer comprising n periods, each period having a thickness ranging from 5 to 10 nm, wherein in the nth period, the composition gradually changes from x+0.005*(n-1)-0.4 to x-0.005n-0.195.
[0070] For example, in the second embodiment of this disclosure, a third stress-relieving layer 530 with a thickness of 100-200 nm is grown to reduce composition. The third stress-relieving layer 530 is a composition-gradient layer comprising 20 cycles, each cycle having a thickness of 5-10 nm. Figure 4 As shown, the thickness of the first cycle is 5–10 nm, and the composition gradually changes from 0.4 to 0.6. This pattern continues in the 10th cycle, where the thickness is 5–10 nm and the composition gradually changes from 0.445 to 0.555. Similarly, the thickness of the 20th cycle is 5–10 nm, and the composition gradually changes from 0.495 to 0.505. The growth process parameters for this compositional gradient include: temperature 1000–1100℃, NH3 flow rate 8000–24000 sccm, pure H2 carrier gas with a flow rate of 30–60 L / min, and a total amount of Group III MO source of 300–600 μmol / min. During the compositional gradient process, the total amount of Group III MO source remains constant. The flow rate of TMAl gradually changes from the flow rate of the corresponding initial composition to the flow rate of the final composition. For example, if the composition changes from 0.4 to 0.6, the flow rate of TMAl gradually changes from the total amount of MO source * 0.4 to the total amount of MO source * 0.6. The growth rate is 0.5–1 μm / h.
[0071] S9: An electrode contact layer is formed on the surface of the third stress relief layer, the electrode contact layer being nAl. x- 0.3 Ga 1.3-x N.
[0072] Specifically, the electrode contact layer 710 comprises nAl with a composition of x-0.3. x-0.3 Ga 1.3-x N. For example, in one specific embodiment, nAl with a thickness of 200–1000 nm and a composition of 0.5 is grown. 0.5 Ga 0.5 N serves as the electrode contact layer 710, which includes SiH4 doping, wherein the SiH4 doping concentration is 3E17 cm⁻¹ to 5E18 cm⁻¹.
[0073] S10: A multi-quantum-well active layer is formed on the electrode contact layer.
[0074] In the embodiments disclosed herein, a multi-quantum-well active layer 720 is grown with 1 to 5 pairs of periods. The barrier layer Al has a composition of 60% to 65% and a thickness of 10 to 20 nm, while the well layer Al has a composition of 20% to 40% and a thickness of 1.5 to 2.5 nm.
[0075] S11: An electron blocking layer, a hole injection layer, and a hole supply layer are sequentially formed on the multi-quantum-well active layer.
[0076] After forming the multi-quantum-well active layer 720, an electron blocking layer 730, a hole injection layer 740, and a hole supply layer 750 are sequentially formed on the multi-quantum-well active layer 720.
[0077] Specifically, firstly, an electron-blocking layer 730 is formed. In some embodiments, the electron-blocking layer (EBL) can be a multi-quantum-well structure with 1 to 5 pairs of periods. The barrier layer has an Al composition of 60% to 80% and a thickness of 6 to 20 nm, while the well layer has an Al composition of 40% to 50% and a thickness of 1.5 to 3.5 nm. In other embodiments, the EBL can also be a single-layer EBL with a composition of 60% to 80% and a thickness of 30 to 70 nm. Next, a hole injection layer 740 is formed on the electron-blocking layer 730. The hole injection layer 740 is a compositionally graded pAlGaN, wherein the Al composition gradually changes from 0.8 to 0.35, the thickness is 15 to 40 nm, and the Mg doping concentration is 1E19 cm⁻¹ to 2E20 cm⁻¹. Subsequently, a hole supply layer 750 is formed on the hole injection layer 740. The hole supply layer 750 is a pGaN with a compositional gradient, a thickness of 1 to 10 nm, and a Mg doping concentration of 1E20 cm-1 to 2E21 cm-1.
[0078] This disclosure embodiment uses nAl with a smooth surface and low composition. x Ga 1-x A multi-quantum-well active layer 720 and an electron blocking layer 730 are grown on the surface of the N-layer. By reducing the well width of the quantum wells and matching the electron blocking layer with appropriate composition and thickness, the spatial separation of the electron and hole wave functions can be reduced, thereby improving the efficiency of carrier radiative coincidence.
[0079] S12: Etch portions of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum-well active layer until the second region of the electrode contact layer is exposed.
[0080] Reference Figure 1After forming the hole supply layer 750, the epitaxial layer is etched to the electrode contact layer 710 using an inductively coupled plasma (ICP) etching process until the second region of the electrode contact layer 710 is exposed, that is, the electrode contact layer 710 is etched into an L-shaped structure.
[0081] S13: A first electrode layer is formed on the second region of the electrode contact layer.
[0082] Next, a first electrode layer 810 is formed on the surface of the second region of the electrode contact layer 710. In some embodiments, the material of the first electrode layer includes at least one selected from chromium, titanium, aluminum, nickel, and gold.
[0083] S14: A second electrode layer is formed on the hole supply layer.
[0084] like Figure 1 As shown, a second electrode layer 820 is formed on the surface of the hole supply layer 750. The second electrode layer 820 is a highly reflective electrode layer. In some embodiments, the material of the second electrode layer includes at least one of nickel, rhodium, and titanium.
[0085] Research and development experiments have revealed that in Al with component x x Ga 1-x Al with composition y is grown on the surface of layer N. y Ga 1-y N layer, Al y Ga 1-y The morphology and relaxation degree of layer N depend not only on the magnitude of the difference between x and y, but also on Al. y Ga 1-y The thickness of layer N, when Al y Ga 1-y When the N layer is extremely thin, Al y Ga 1-y Layer N still maintains its connection with Al. x Ga 1-x The N layers have the same lattice constant, only when Al y Ga 1-y When the thickness of layer N is greater than a certain thickness, Al y Ga 1-y Relaxation will only begin at layer N, and the system will gradually recover to Al. y Ga 1-y The lattice constant of the N-layer itself. Using Al x Ga 1-x The N-layer composition has a certain difference in Al y Ga 1-y N, and control Al y Ga 1-yThe thickness of the N layer, not exceeding a certain value, can maintain lattice uniformity and reduce the average composition. In Al with composition x... x Ga 1-x An Al layer of a certain thickness is grown on the surface of layer N. y Ga 1-y N, where y < x, Al y Ga 1-y The lattice constant of the N-layer and Al x Ga 1-x Layer N remains consistent, but Al y Ga 1-y N-layer Al received Al x Ga 1-x The compressive stress in layer N, and then in Al y Ga 1-y An Al layer of a certain thickness is grown on the surface of layer N. z Ga 1-z N, where y < z < x, then Al z Ga 1-z Layer N received Al x Ga 1-x N layer through Al y Ga 1-y The compressive stress on it after layer N, but due to the presence of lower-content Al in the middle. y Ga 1-y In layer N, the compressive stress is higher than that in Al. x Ga 1-x Al is directly grown on the N layer. z Ga 1-z The compressive stress generated by the N-layer is small. This process reduces the compressive stress of the high-concentration template layer on the low-concentration growth layer, achieving both composition reduction and lattice constant maintenance. The UVB epitaxial structure obtained by the above process is used in the fabrication of UVB LEDs, resulting in UVB LEDs with emission peak wavelengths in the range of 305 nm to 313 nm. By repeatedly applying the above principle, the AlN template layer can be gradually reduced to an even lower Al composition. x Ga 1-x N, and reduces the probability of dislocation generation during this process, thereby increasing nAl x Ga 1-x Improving the crystal quality of the N-layer and enhancing surface smoothness, thereby reducing the half-width of the quantum well emission spectrum. nAl x Ga 1-x Improving the crystal quality of the N-layer can also reduce the defect density of the quantum well layer, thereby improving the light maintenance efficiency of the LED.
[0086] The method for preparing UVB epitaxial wafers provided in this disclosure yields an nAlGaN layer with a composition of 50%. A UVB epitaxial wafer grown using a single-component transition layer is used as a control process. The UVB epitaxial wafer grown with a single-component transition layer on AlN is compared with the UVB epitaxial wafer grown using the preparation process in the first and second embodiments of this disclosure. Figure 5 To achieve the desired morphology of UVB epitaxial wafers grown using a single-component transition layer, the following methods were employed. Figure 5 There are about 30 white hexagonal protrusions, which are caused by the lattice mismatch between the AlN template and the 50% nAlGaN composition. Figure 6 and Figure 7 The absence of white hexagonal protrusions indicates that the transition through multi-period thin layers reduced the lattice mismatch between the AlN template and nAlGaN, thus decreasing the number of defects.
[0087] The UVB epitaxial wafers with a single-component transition layer, as well as the UVB epitaxial wafers obtained in the first and second embodiments of this disclosure, were respectively fabricated into chips with a size of 20mil*20mil. After packaging, the emission spectra of the three LED chips were tested, such as... Figure 8 As shown, compared to UVB epitaxial wafers grown using a single-component transition layer, the peak intensity of the emission spectrum of LED chips prepared using UVB epitaxial wafers in the first and second embodiments of this disclosure is improved, i.e. Figure 8 The implementation cases 1 and 2 are shown, and the half-width is reduced from 13.5nm to around 11nm. The three packaged chips were placed on the same aging rack for a room temperature and humidity aging test at a drive current of 100mA. The light retention results are as follows: Figure 9 As shown. By Figure 9 As can be seen, compared with UVB epitaxial wafers grown using a single-component transition layer, the light maintenance efficiency of LED chips prepared using UVB epitaxial wafers in the first and second embodiments of this disclosure is improved, increasing from 89.9% to 97.7% to 98.6%.
[0088] This invention provides a UVB epitaxial wafer and its preparation method. By repeatedly growing thin layers with gradually increasing composition, the Al composition is reduced while maintaining a constant lattice constant. Through repeated application of this principle, the AlN template layer is gradually reduced to an even lower Al composition. x Ga 1-x N, and reduces the probability of dislocation generation during this process, thereby increasing nAl x Ga 1-x Improving the crystal quality of the N-layer and enhancing surface smoothness reduces the half-width of the quantum well's emission spectrum, thereby increasing the LED light maintenance rate.
[0089] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, such as the combination of technical features between embodiments, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A UVB epitaxial wafer, characterized in that, include: The substrate and the buffer layer on the first surface of the substrate; An AlN layer located on the buffer layer; Al with component x x Ga 1-x N layers, where 0.8 ≤ x ≤ 0.9; A superlattice layer, the superlattice layer comprising a stress relief layer and a transition layer, the stress relief layer comprising a first stress relief layer, a second stress relief layer and a third stress relief layer, each stress relief layer comprising a plurality of periods, each period having a thickness ranging from 5 to 10 nm; Electrode contact layer; A multi-quantum-well active layer, wherein the multi-quantum-well active layer has an L-shaped structure, including a first region and a second region, wherein the thickness of the first region is greater than the thickness of the second region; An electron blocking layer, a hole injection layer, and a hole supply layer are stacked sequentially, wherein the electron blocking layer, the hole injection layer, and the hole supply layer cover the first region of the multi-quantum-well active layer; The first electrode layer is located on the second region of the multi-quantum-well active layer; The second electrode layer is located on the hole supply layer.
2. The UVB epitaxial wafer as described in claim 1, characterized in that, The transition layer includes a first transition layer and a second transition layer, wherein the first transition layer is located between the first stress relief layer and the second stress relief layer, and the second transition layer is located between the second stress relief layer and the third stress relief layer.
3. The UVB epitaxial wafer as described in claim 2, characterized in that, The material of the first transition layer comprises Al with a composition of x-0.
1. x-0.1 Ga 1.1-x N, the material of the second transition layer comprises Al with a composition of x-0.
2. x-0.2 Ga 1.2-x N.
4. The UVB epitaxial wafer as described in claim 1, characterized in that, The first stress relief layer comprises n cycles, each cycle comprising 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first thin layer has a composition of x + 0.005*(n-1) - 0.2, the second thin layer has a composition of x + 0.0025n - 0.1525, the third thin layer has a composition of x - 0.1, the fourth thin layer has a composition of x - 0.0025n - 0.0475, and the fifth thin layer has a composition of x - 0.005n + 0.
005.
5. The UVB epitaxial wafer as described in claim 1, characterized in that, The first stress relief layer is a composition gradient layer comprising n periods, with each period having a thickness ranging from 5 to 10 nm. In the nth period, the composition gradually changes from x+0.005*(n-1)-0.2 to x-0.005n+0.
005.
6. The UVB epitaxial wafer as described in claim 1, characterized in that, The second stress relief layer comprises n cycles, each cycle comprising 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first thin layer has a composition of x + 0.005*(n-1) - 0.3, the second thin layer has a composition of x + 0.0025n - 0.2525, the third thin layer has a composition of x - 0.2, the fourth thin layer has a composition of x - 0.0025n - 0.1475, and the fifth thin layer has a composition of x - 0.005n - 0.
095.
7. The UVB epitaxial wafer as described in claim 1, characterized in that, The second stress relief layer is a composition gradient layer comprising n cycles, with each cycle having a thickness ranging from 5 to 10 nm. In the nth cycle, the composition gradually changes from x+0.005*(n-1)-0.3 to x-0.005n-0.
095.
8. The UVB epitaxial wafer as described in claim 1, characterized in that, The third stress relief layer comprises n cycles, each cycle comprising 5 thin layers, each thin layer having a thickness ranging from 1 to 2 nm. In the nth cycle, the first thin layer has a component of x + 0.005*(n-1) - 0.4, the second thin layer has a component of x + 0.0025n - 0.3525, the third thin layer has a component of x - 0.3, the fourth thin layer has a component of x - 0.0025n - 0.2475, and the fifth thin layer has a component of x - 0.005n - 0.
195.
9. The UVB epitaxial wafer as described in claim 1, characterized in that, The third stress relief layer is a composition gradient layer comprising n cycles, with each cycle having a thickness ranging from 5 to 10 nm. In the nth cycle, the composition gradually changes from x+0.005*(n-1)-0.4 to x-0.005n-0.
195.
10. The UVB epitaxial wafer as described in claim 1, characterized in that, The electrode contact layer comprises nAl with a composition of x-0.
3. x-0.3 Ga 1.3-x N.
11. The UVB epitaxial wafer as described in claim 1, characterized in that, The Al with component x x Ga 1-x The thickness of the N layer ranges from 50 to 200 nm, the thickness of the first transition layer ranges from 200 to 400 nm, the thickness of the second transition layer ranges from 200 to 400 nm, and the thickness of the electrode contact layer ranges from 200 to 1000 nm.
12. A method for preparing a UVB epitaxial wafer according to any one of claims 1-11, characterized in that, Including the following steps: A substrate is provided, and a buffer layer is formed on one side of the first surface of the substrate; An AlN layer is formed on the surface of the buffer layer; An Al with composition x is formed on the AlN layer. x Ga 1-x N layers, where 0.8 ≤ x ≤ 0.9; In the Al x Ga 1-x A first stress relief layer is formed on the surface of the N layer. The first stress relief layer contains several periods, and the thickness of each period ranges from 5 to 10 nm. A first transition layer is formed on the surface of the first stress relief layer, wherein the first transition layer is Al. x-0.1 Ga 1.1-x N; A second stress relief layer is formed on the surface of the first transition layer. The second stress relief layer contains several periods, and the thickness of each period ranges from 5 to 10 nm. A second transition layer is formed on the surface of the second stress relief layer, and the second transition layer is Al. x-0.2 Ga 1.2-x N; A third stress relief layer is formed on the surface of the second transition layer. The third stress relief layer contains several periods, and the thickness of each period ranges from 5 to 10 nm. An electrode contact layer is formed on the surface of the third stress relief layer, and the electrode contact layer is nAl. x-0.3 Ga 1.3-x N; A multi-quantum-well active layer is formed on the electrode contact layer; An electron blocking layer, a hole injection layer, and a hole supply layer are sequentially formed on the multi-quantum-well active layer. Etch portions of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum-well active layer until the second region of the electrode contact layer is exposed; A first electrode layer is formed on the second region of the electrode contact layer; A second electrode layer is formed on the hole supply layer.
13. The method for preparing a UVB epitaxial wafer as described in claim 12, characterized in that, The step of forming a buffer layer on one side of the first surface of the substrate includes the following steps: forming the buffer layer by a magnetron sputtering growth process, wherein the magnetron sputtering growth process conditions include: a temperature range of 550–700°C, a sputtering power range of 1000–4000W, a nitrogen flow rate range of 80–200 sccm, an oxygen flow rate range of 0.5–5 sccm, an argon flow rate range of 0.1–40 sccm, and a deposition time range of 16–100 s.
14. The method for preparing a UVB epitaxial wafer as described in claim 12, characterized in that, The step of forming an AlN layer on the surface of the buffer layer includes: An AlN 3D layer was formed on the buffer layer using a vapor phase epitaxial growth process. An AlN 2D layer was formed on the buffer layer using a vapor phase epitaxial growth process.
15. The method for preparing a UVB epitaxial wafer as described in claim 12, characterized in that, The etching of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum-well active layer includes the following steps: ICP etching was used to etch part of the hole supply layer, hole injection layer, electron blocking layer, and multi-quantum well active layer.