Ultraviolet laser epitaxial wafer and preparation method thereof

Abstract

The present invention discloses an ultraviolet laser epitaxial wafer and a preparation method thereof. The preparation method comprises: preparing a first AlGaN confinement layer on an n-type GaN layer, wherein the Al component concentration of the first AlGaN confinement layer increases along a first direction, the first direction being a direction from the n-type GaN layer toward the first AlGaN confinement layer; preparing a first waveguide layer on the first AlGaN confinement layer; preparing a quantum well light-emitting layer on the first waveguide layer, wherein the light emission wavelength range of the quantum well light-emitting layer includes 330nm to 390nm; preparing a second waveguide layer on the quantum well light-emitting layer; and preparing a second AlGaN confinement layer on the second waveguide layer, wherein the Al component concentration of the second AlGaN confinement layer decreases along the first direction.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, in particular to an ultraviolet laser epitaxial wafer and a preparation method thereof. Background Art

[0002] GaN-based materials are also called III-nitride materials (including InN, GaN, AlN, InGaN, AlGaN, etc., with a bandgap width ranging from 0.7 to 6.2 eV). Their spectrum covers the near-infrared to deep ultraviolet bands. They are considered to be the third generation of semiconductors after Si and GaAs, and have important application value in the field of optoelectronics. Compared with blue-green lasers, ultraviolet lasers are more difficult. So far, only Nichia Corporation of Japan can grow 375nm ultraviolet laser products, but the price of a single tube core is as high as tens of thousands of yuan. Internationally, there are only a few research institutes in Japan, the United States and China that can achieve ultraviolet lasing. Summary of the Invention

[0003] In view of this, the present invention provides an ultraviolet laser epitaxial wafer and a method for preparing the same, in order to at least partially solve at least one of the above technical problems.

[0004] As one aspect of the present invention, a method for preparing an ultraviolet laser epitaxial wafer is disclosed, comprising:

[0005] forming a first AlGaN confinement layer on the n-type GaN layer, wherein the Al component concentration of the first AlGaN confinement layer increases along a first direction, the first direction being a direction from the n-type GaN layer toward the first AlGaN confinement layer;

[0006] forming a first waveguide layer on the first AlGaN confinement layer;

[0007] A quantum well light-emitting layer is prepared on the first waveguide layer 3, wherein the light-emitting wavelength range of the quantum well light-emitting layer includes 330nm to 390nm;

[0008] preparing a second waveguide layer on the quantum well light-emitting layer; and

[0009] A second AlGaN confinement layer is formed on the second waveguide layer, wherein the Al composition concentration of the second AlGaN confinement layer decreases along the first direction.

[0010] As another aspect of the present invention, an ultraviolet laser epitaxial wafer is also disclosed, comprising:

[0011] n-type GaN layer 1;

[0012] a first AlGaN confinement layer 2 disposed on the n-type GaN layer 1, wherein the Al component concentration of the first AlGaN confinement layer 2 increases along a first direction, where the first direction is from the n-type GaN layer 1 toward the first AlGaN confinement layer 2;

[0013] A first waveguide layer 3, provided on the first AlGaN confinement layer 2;

[0014] A quantum well light-emitting layer 4 is provided on the first waveguide layer 3, wherein the light-emitting wavelength range of the quantum well light-emitting layer 4 is 330 nm to 390 nm;

[0015] A second waveguide layer 5 is provided on the quantum well light-emitting layer 4; and

[0016] a second AlGaN confinement layer 6, disposed on the second waveguide layer 5, wherein the Al composition concentration of the second AlGaN confinement layer 6 decreases along the first direction;

[0017] The first AlGaN confinement layer 2 and the second AlGaN confinement layer 6 are used to prevent carrier leakage.

[0018] Based on the above technical solution, the ultraviolet laser epitaxial wafer and the preparation method thereof of the present invention have at least one of the following beneficial effects:

[0019] The ultraviolet laser epitaxial wafer and preparation method provided by the present invention replace upper and lower AlGaN confinement layers with uniform composition or superlattice structure with confinement layers with gradient Al composition (i.e., first AlGaN confinement layer and second AlGaN confinement layer). On the one hand, the composition difference between the AlGaN confinement layer and the waveguide layer (i.e., between the first AlGaN confinement layer and the first waveguide layer, and between the second AlGaN confinement layer and the second waveguide layer) is increased, thereby enhancing the optical field confinement of the laser. On the other hand, polarization doping with gradient Al composition can reduce the incorporation of Mg dopants, effectively reducing the absorption loss of the laser. At the same time, the high Al composition AlGaN electron blocking layer is removed, thereby reducing the operating voltage of the ultraviolet laser, enhancing the carrier confinement effect, preventing carrier leakage, and ultimately improving the performance of the ultraviolet laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of a method for preparing an ultraviolet laser epitaxial wafer provided in an embodiment of the present invention;

[0021] Figure 2 It is a schematic diagram of the structure of the ultraviolet laser epitaxial wafer provided in an embodiment of the present invention.

[0022] Description of Reference Numerals

[0023] 1: n-type GaN layer;

[0024] 2: First AlGaN confinement layer;

[0025] 3: first waveguide layer;

[0026] 4: Quantum well light-emitting layer;

[0027] 5: second waveguide layer;

[0028] 6: Second AlGaN confinement layer;

[0029] 7: substrate;

[0030] 8: GaN nucleation layer;

[0031] 9: Undoped GaN layer;

[0032] 10: p-type GaN layer. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0034] At present, the main difficulties restricting ultraviolet laser lasing are:

[0035] (1) Since the quantum well of the ultraviolet laser has a very low In component or no In at all, the quantum well luminescence efficiency of the ultraviolet laser is low.

[0036] (2) Since ultraviolet lasers use a large amount of AlGaN with a high Al content, the epitaxial wafer is subject to high stress and is prone to cracks.

[0037] (3) It is difficult to dope the n-type AlGaN layer and the p-type AlGaN layer with high Al content, resulting in high device resistance and low carrier injection efficiency of the UV laser.

[0038] (4) The AlGaN / (Al, In)GaN quantum well has a shallow depth, resulting in large carrier leakage. Especially when a large current (for example, the current can be 3A) is injected, there is a serious leakage problem of electrons and holes.

[0039] The present invention discloses a method for preparing an ultraviolet laser epitaxial wafer, comprising:

[0040] A method for preparing an ultraviolet laser epitaxial wafer, comprising:

[0041] forming a first AlGaN confinement layer 2 on the n-type GaN layer 1, wherein the Al component concentration of the first AlGaN confinement layer 2 increases along a first direction, and the first direction is a direction from the n-type GaN layer 1 toward the first AlGaN confinement layer 2;

[0042] Preparing a first waveguide layer 3 on the first AlGaN confinement layer 2;

[0043] A quantum well light-emitting layer 4 is prepared on the first waveguide layer 3, wherein the light-emitting wavelength range of the quantum well light-emitting layer 4 is 330 nm to 390 nm;

[0044] preparing a second waveguide layer 5 on the quantum well light-emitting layer 4; and

[0045] A second AlGaN confinement layer 6 is formed on the second waveguide layer 5 , wherein the Al composition concentration of the second AlGaN confinement layer 6 decreases along the first direction.

[0046] In some embodiments of the present invention, the Al composition concentration of the first AlGaN confinement layer 2 and the second AlGaN confinement layer 6 is 5% to 30%.

[0047] In some embodiments of the present invention, the preparation temperature of the first AlGaN confinement layer 2 is 1000° C. to 1200° C.;

[0048] The thickness of the first AlGaN confinement layer 2 is 0.5 μm to 1 μm.

[0049] In some embodiments of the present invention, the preparation temperature of the second AlGaN confinement layer 6 is 1000° C. to 1200° C.;

[0050] The thickness of the second AlGaN confinement layer 6 is 0.5 μm to 1 μm.

[0051] In some embodiments of the present invention,

[0052] The doping concentration of silicon in the first AlGaN confinement layer 2 is 0;

[0053] The magnesium doping concentration in the second AlGaN confinement layer 6 is zero.

[0054] In some embodiments of the present invention, the preparation method further comprises:

[0055] Preparing a GaN nucleation layer 8 on a substrate 7;

[0056] forming a non-doped GaN layer 9 on the GaN nucleation layer 8;

[0057] forming the n-type GaN layer 1 on the non-doped GaN layer 9; and

[0058] A p-type GaN layer 10 is formed on the second AlGaN confinement layer 6 .

[0059] In some embodiments of the present invention, the preparation temperature of the GaN nucleation layer 8 is 500° C. to 620° C.;

[0060] The thickness of the GaN nucleation layer 8 is 20 nm to 30 nm.

[0061] In some embodiments of the present invention, the substrate 7 includes any one of a sapphire substrate, a gallium nitride substrate, a silicon carbide substrate or a silicon substrate.

[0062] The present invention also discloses an ultraviolet laser epitaxial wafer, comprising:

[0063] n-type GaN layer 1;

[0064] a first AlGaN confinement layer 2 disposed on the n-type GaN layer 1, wherein the Al composition concentration of the first AlGaN confinement layer 2 increases along a first direction, the first direction being a direction from the n-type GaN layer 1 toward the first AlGaN confinement layer 2;

[0065] A first waveguide layer 3 is provided on the first AlGaN confinement layer 2;

[0066] A quantum well light-emitting layer 4 is provided on the first waveguide layer 3, wherein the light-emitting wavelength range of the quantum well light-emitting layer 4 is 330 nm to 390 nm;

[0067] A second waveguide layer 5 is provided on the quantum well light-emitting layer 4; and

[0068] a second AlGaN confinement layer 6 disposed on the second waveguide layer 5, wherein the Al composition concentration of the second AlGaN confinement layer 6 decreases along the first direction;

[0069] The first AlGaN confinement layer 2 and the second AlGaN confinement layer 6 are used to prevent carrier leakage.

[0070] In some embodiments of the present invention, the ultraviolet laser epitaxial wafer further includes:

[0071] substrate 7;

[0072] A GaN nucleation layer 8 is provided on the substrate 7;

[0073] an undoped GaN layer 9 disposed on the GaN nucleation layer 8, wherein the n-type GaN layer 1 is disposed on the undoped GaN layer 9; and

[0074] The p-type GaN layer 10 is provided on the second AlGaN confinement layer 6 .

[0075] Figure 1 It is a flow chart of the method for preparing an ultraviolet laser epitaxial wafer provided in an embodiment of the present invention.

[0076] In an embodiment of the present invention, a method for preparing an ultraviolet laser epitaxial wafer is disclosed, such as Figure 1 Shown, including:

[0077] S1: preparing a GaN nucleation layer 8 on the substrate 7.

[0078] In this embodiment, the substrate 7 is annealed in a hydrogen atmosphere to clean the surface of the substrate. The substrate may include a sapphire, gallium nitride, silicon carbide or silicon substrate.

[0079] In this embodiment, the temperature is lowered to 500°C to 620°C, for example, 500°C, 530°C, 580°C, or 620°C, to grow a GaN nucleation layer 8 with a thickness of 20 to 30 nm, providing nucleation centers for subsequent material growth. The thickness of the GaN nucleation layer 8 can be, for example, 20 nm, 25 nm, or 30 nm.

[0080] S2: preparing a non-doped GaN layer 9 on the GaN nucleation layer 8 .

[0081] In this embodiment, a non-doped GaN layer 9 is epitaxially grown on the GaN nucleation layer 8 to provide a template for subsequent high-quality growth of materials.

[0082] S3 : forming an n-type GaN layer 1 on the undoped GaN layer 9 .

[0083] S4: forming a first AlGaN confinement layer 2 on the n-type GaN layer 1 .

[0084] In this embodiment, a first AlGaN confinement layer 2 is formed on an n-type GaN layer 1. The Al component concentration of the first AlGaN confinement layer 2 increases from the n-type GaN layer 1 toward the first AlGaN confinement layer 2. A high electron concentration is achieved in the first AlGaN confinement layer 2 by utilizing the polarization effect.

[0085] In this embodiment, the Al composition concentration in the first AlGaN confinement layer 2 may be 5% to 30%, for example, 5%, 10%, 15%, 25%, or 30%. The preparation temperature of the first AlGaN confinement layer 2 may be 1000° C. to 1200° C., for example, 1000° C., 1100° C., or 1200° C. The thickness of the first AlGaN confinement layer 2 may be 0.5 μm to 1 μm, for example, 0.5 μm, 0.75 μm, or 1 μm. The silicon doping concentration in the first AlGaN confinement layer 2 may be 0.

[0086] S5 : forming a first waveguide layer 3 on the first AlGaN confinement layer 2 .

[0087] In this embodiment, a first waveguide layer 3 is formed on the first AlGaN confinement layer 2. Light is confined within the waveguide layer by utilizing the refractive index difference between the first AlGaN confinement layer 2 and the undoped lower waveguide layer. Because the Al composition in the first AlGaN confinement layer 2 gradually increases, when the average Al composition remains the same, the Al composition of the first AlGaN confinement layer 2 near the first waveguide layer 3 is higher than that of a uniform AlGa composition or a superlattice structure. This increases the composition difference between the first AlGaN confinement layer 2 and the first waveguide layer 3, thereby enhancing the optical field confinement of the laser.

[0088] S6: A quantum well light-emitting layer 4 is prepared on the first waveguide layer 3. The quantum well light-emitting layer 4 may include a single quantum well structure consisting of a quantum well sublayer and a quantum barrier sublayer. The quantum well sublayer is made of AlGaN, GaN, InGaN, or AlInGaN material, and the quantum barrier sublayer is made of AlGaN or GaN. The quantum well light-emitting layer 5 has an emission wavelength range of 300 nm to 390 nm, for example, 300 nm, 330 nm, 340 nm, 350 nm, and 390 nm. However, the quantum well light-emitting layer 5 is not limited thereto and may also include a multi-quantum well structure.

[0089] S7: preparing a second waveguide layer 5 on the quantum well light-emitting layer 4 .

[0090] S8: A second AlGaN confinement layer 6 is prepared on the second waveguide layer 5. The refractive index difference between the second AlGaN confinement layer 6 and the second waveguide layer 5 is used to confine light in the waveguide layer. The Al component concentration of the second AlGaN confinement layer 6 decreases in the direction from the n-type GaN layer 1 to the first AlGaN confinement layer 2. The polarization effect is used to achieve a high hole concentration in the second AlGaN confinement layer 6, solving the technical problem of the difficulty in doping the existing high Al component p-type AlGaN layer. At the same time, the Mg doping concentration is reduced, reducing the absorption loss of the ultraviolet laser. In addition, since the Al component in the second AlGaN confinement layer 6 gradually decreases in the direction away from the second waveguide layer 5, the Al component of the second AlGaN confinement layer 6 close to the second waveguide layer 5 is higher, which can effectively prevent the leakage of carriers.

[0091] In this embodiment, the Al component concentration in the second AlGaN confinement layer 6 may include 5% to 30%, for example, 5%, 10%, 15%, 25%, and 30%; the preparation temperature of the second AlGaN confinement layer 6 may include 1000°C to 1200°C, for example, 1000°C, 1100°C, and 1200°C; the thickness of the second AlGaN confinement layer 6 may include 0.5μm to 1μm, for example, 0.5μm, 0.75μm, and 1μm; the magnesium doping concentration in the second AlGaN confinement layer 6 may be 0.

[0092] S9: forming a p-type GaN layer 10 on the second AlGaN confinement layer 6 to form an ohmic contact layer of the ultraviolet laser epitaxial wafer.

[0093] Figure 2 It is a schematic diagram of the structure of the ultraviolet laser epitaxial wafer provided in an embodiment of the present invention.

[0094] In one embodiment of the present invention, a UV laser epitaxial wafer is also disclosed.

[0095] like Figure 2 As shown, the ultraviolet laser epitaxial wafer includes:

[0096] A GaN nucleation layer 8 is provided on a substrate 7;

[0097] An undoped GaN layer 9 is provided on the GaN nucleation layer 8;

[0098] n-type GaN layer 1, disposed on the undoped GaN layer 9;

[0099] A first AlGaN confinement layer 2 is provided on the n-type GaN layer 1, wherein the Al component concentration of the first AlGaN confinement layer 2 increases along a first direction, where the first direction is from the n-type GaN layer 1 toward the first AlGaN confinement layer 2;

[0100] A first waveguide layer 3 is provided on the first AlGaN confinement layer 2;

[0101] The quantum well light-emitting layer 4 is provided on the first waveguide layer 3, wherein the light-emitting wavelength range of the quantum well light-emitting layer 4 includes 330nm to 390nm;

[0102] A second waveguide layer 5 is provided on the quantum well light emitting layer 4;

[0103] a second AlGaN confinement layer 6 disposed on the second waveguide layer 5, wherein the Al composition concentration of the second AlGaN confinement layer 6 decreases along the first direction;

[0104] The p-type GaN layer 10 is provided on the second AlGaN confinement layer 6 .

[0105] In this embodiment, the UV laser epitaxial wafer and its fabrication method do not employ the high-Al-composition p-type AlGaN electron-blocking layer (EBL) used in related art. Instead, a high-Al-composition AlGaN near the waveguide layer forms a barrier with the waveguide layer. Specifically, a first waveguide layer 3 is provided on a first AlGaN confinement layer 2, with the Al composition of the first AlGaN confinement layer 2 gradually increasing as it approaches the first waveguide layer 3. Furthermore, a second AlGaN confinement layer 6 is provided on a second waveguide layer 5, with the Al composition of the second AlGaN confinement layer 6 gradually increasing as it approaches the second waveguide layer 5, thereby achieving carrier blocking. By removing the high-Al-composition AlGaN electron-blocking layer, the operating voltage of the UV laser can be reduced, carrier injection efficiency can be increased, carrier leakage can be prevented, and ultimately, the performance of the UV laser can be improved.

[0106] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0107] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an ultraviolet laser epitaxial wafer, comprising: A first AlGaN confinement layer (2) is prepared on the n-type GaN layer (1), wherein the Al component concentration of the first AlGaN confinement layer (2) increases along a first direction, the first direction being a direction from the n-type GaN layer (1) toward the first AlGaN confinement layer (2); Preparing a first waveguide layer (3) on the first AlGaN confinement layer (2); A quantum well light-emitting layer (4) is prepared on the first waveguide layer (3), wherein the light-emitting wavelength of the quantum well light-emitting layer (4) ranges from 330 nm to 390 nm; preparing a second waveguide layer (5) on the quantum well light-emitting layer (4); and preparing a second AlGaN confinement layer (6) on the second waveguide layer (5), wherein the Al component concentration of the second AlGaN confinement layer (6) decreases along the first direction; The preparation method further comprises: Preparing a GaN nucleation layer (8) on a substrate (7); Preparing a non-doped GaN layer (9) on the GaN nucleation layer (8); preparing the n-type GaN layer (1) on the non-doped GaN layer (9); and A p-type GaN layer (10) is prepared on the second AlGaN confinement layer (6) to form an ohmic contact layer of the ultraviolet laser wafer.

2. The preparation method according to claim 1, wherein The Al component concentration of the first AlGaN confinement layer (2) and the second AlGaN confinement layer (6) is 5% to 30%.

3. The preparation method according to claim 1, wherein The preparation temperature of the first AlGaN confinement layer (2) is 1000° C. to 1200° C.; The thickness of the first AlGaN confinement layer (2) is 0.5 μm to 1 μm.

4. The preparation method according to claim 1, wherein The preparation temperature of the second AlGaN confinement layer (6) is 1000°C to 1200°C; The thickness of the second AlGaN confinement layer (6) is 0.5 μm to 1 μm.

5. The preparation method according to claim 1, wherein The doping concentration of silicon in the first AlGaN confinement layer (2) is 0; The doping concentration of magnesium in the second AlGaN confinement layer (6) is 0.

6. The preparation method according to claim 1, wherein The preparation temperature of the GaN nucleation layer (8) is 500°C to 620°C; The thickness of the GaN nucleation layer (8) is 20 nm to 30 nm.

7. The preparation method according to claim 1, wherein The substrate (7) includes any one of a sapphire substrate, a gallium nitride substrate, a silicon carbide substrate or a silicon substrate.

8. An ultraviolet laser epitaxial wafer, comprising: n-type GaN layer (1); a first AlGaN confinement layer (2) disposed on the n-type GaN layer (1), wherein the Al component concentration of the first AlGaN confinement layer (2) increases along a first direction, the first direction being a direction from the n-type GaN layer (1) toward the first AlGaN confinement layer (2); A first waveguide layer (3) is provided on the first AlGaN confinement layer (2); A quantum well light-emitting layer (4) is provided on the first waveguide layer (3), wherein the light-emitting wavelength range of the quantum well light-emitting layer (4) includes 330 nm to 390 nm; a second waveguide layer (5) disposed on the quantum well light-emitting layer (4); and a second AlGaN confinement layer (6) disposed on the second waveguide layer (5), wherein the Al component concentration of the second AlGaN confinement layer (6) decreases along the first direction; Wherein, the first AlGaN confinement layer (2) and the second AlGaN confinement layer (6) are used to prevent carrier leakage; The ultraviolet laser epitaxial wafer further comprises: substrate (7); A GaN nucleation layer (8) is provided on the substrate (7); an undoped GaN layer (9) disposed on the GaN nucleation layer (8), wherein the n-type GaN layer (1) is disposed on the undoped GaN layer (9); and A p-type GaN layer (10) is provided on the second AlGaN confinement layer (6).

Images