GaN-based blue laser epitaxial structure and preparation method thereof

Abstract

This invention relates to the field of semiconductor laser technology, specifically to an epitaxial structure of a GaN-based blue laser and its fabrication method. The structure includes a substrate on which an N-type GaN layer, an N-type lower confinement layer, an N-type lower waveguide layer, an active region, an upper waveguide layer, a U-type capping layer, a P-type electron blocking layer, a P-type upper confinement layer, and a P-type contact layer are sequentially stacked. The P-type electron blocking layer comprises a sequentially stacked AlN sublayer and a P-type InAlGaN sublayer. The P-type electron blocking layer of this invention utilizes the piezoelectric polarization and spontaneous polarization of the P-type InAlGaN sublayer to induce a large band bend at the heterojunction, placing the P-type dopant acceptor energy level below the Fermi level, thereby increasing the ionization rate of the P-type dopant acceptor at the cross-section and thus increasing the hole concentration. Furthermore, the use of a high-Al composition AlN sublayer near the active region can raise the energy band, confine electron overflow in the active region, and reduce non-radiative recombination of electrons and holes in the non-recombination region, thereby improving the luminous efficiency of the device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to a GaN-based blue laser epitaxial structure and its fabrication method. Background Technology

[0002] Among optoelectronic devices fabricated using GaN, GaN-based blue LEDs (laser diodes) possess characteristics such as low driving power consumption, high output energy, small size, and stable performance, and have significant application value in data storage, laser display, and laser lighting. The development and challenges of GaN-based lasers are similar to those of GaN-based LEDs (light-emitting diodes), including issues related to crystal growth quality, P-type doping, and electron leakage. Mg, as an acceptor impurity that generates holes, exhibits high activation energy and low ionization rate in AlGaN alloys. Furthermore, the activation energy increases linearly with increasing Al content (the activation energy of Mg acceptors in GaN at room temperature is 160–220 meV, while in AlGaN it can reach as high as 200–510 meV). This results in a significantly lower hole concentration in AlGaN compared to GaN, making it difficult to achieve high hole concentration and low resistance in P-type AlGaN. Furthermore, due to the small effective mass and high mobility of electrons, electrons can easily cross the quantum well recombination region to reach the non-radiative recombination region and recombine with holes, reducing the effective radiative recombination efficiency and thus reducing the luminescence efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a GaN-based blue laser epitaxial structure and its fabrication method, which can at least solve some of the defects in the prior art.

[0004] To achieve the above objectives, the technical solution of the present invention is a GaN-based blue laser epitaxial structure, comprising a substrate, wherein an N-type GaN layer, an N-type lower confinement layer, an N-type lower waveguide layer, an active region, an upper waveguide layer, a U-type capping layer, a P-type electron blocking layer, a P-type upper confinement layer, and a P-type contact layer are sequentially stacked on the substrate; the P-type electron blocking layer comprises an AlN sublayer and a P-type InAlGaN sublayer sequentially stacked.

[0005] As one implementation method, the p-type InAlGaN sublayer is a single-layer P-type In with varying Al composition. x Al y Ga 1-x-y N-type sublayers, or the P-type InAlGaN sublayers being multilayered P-type In with varying Al composition. x Al y Ga 1-x-y A composite structure in which N sub-layers are stacked sequentially, where 0≤x <y<1,0<x+y<1。

[0006] As one implementation method, the p-type InAlGaN sublayer is a multilayer p-type In with a constant Al composition. x Al y Ga 1-x-y The superlattice structure of cyclically stacked N-type sublayers, or the P-type InAlGaN sublayers being multilayered P-type In with varying Al composition. x Al y Ga 1-x-y A superlattice structure with N-sublayer cyclic stacking, where 0≤x <y<1,0≤y<1,0<x+y<1。

[0007] As one implementation method, the p-type InAlGaN sublayer is a single-layer / multi-layer p-type In with a constant Al composition. x Al y Ga 1-x-y P-type In with variations in N-sublayer and monolayer / multilayer Al composition x Al y Ga 1-x-y A superlattice structure with alternating N-sublayers, where 0 ≤ x <y<1,0<x+y<1。

[0008] As one implementation method, the P-type In with Al composition variation x Al y Ga 1-x-y The Al composition of the N sublayer is linearly decreasing, linearly increasing, linearly increasing again, linearly decreasing again, linearly decreasing again, linearly increasing again, gradient increasing, gradient decreasing, gradient decreasing again, or gradient increasing again and gradient decreasing again.

[0009] As one implementation method, the thickness of the AlN sublayer is d1, and the P-type In... x Al y Ga 1-x-y The thickness of the N-sublayer is d2, 0 <d1<d2<10nm。

[0010] As one embodiment, the U-shaped capping layer is a U-shaped GaN layer, and the growth temperature of the U-shaped GaN layer is lower than the growth temperature of the P-shaped electron blocking layer.

[0011] As one implementation method, the P-type contact layer is a P-type In a Al b Ga 1-a-b There are N layers, where 0 ≤ a < 1, 0 ≤ b < 1, and 0 ≤ a + b < 1.

[0012] As one embodiment, the N-type lower confinement layer includes a first N-type lower confinement layer, an N-type stress relief layer, and a second N-type lower confinement layer sequentially disposed on the N-type GaN layer.

[0013] The present invention also provides a method for fabricating the epitaxial structure of a GaN-based blue laser as described in any one of the above claims, comprising the following steps:

[0014] S1. An N-type GaN layer, an N-type lower confinement layer, an N-type lower waveguide layer, an active region, an upper waveguide layer, and a U-type capping layer are epitaxially grown sequentially on the substrate.

[0015] S2. AlN sublayers and P-type InAlGaN sublayers are sequentially stacked on the U-shaped capping layer to form a P-type electron blocking layer.

[0016] S3. Epitaxially grow a P-type upper confinement layer and a P-type contact layer on the P-type electron blocking layer.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The P-type electron blocking layer of the present invention is composed of AlN sublayer and P-type InAlGaN sublayer stacked sequentially. The piezoelectric polarization and spontaneous polarization of the P-type InAlGaN sublayer induce a huge band bend at the heterojunction, so that the P-type dopant acceptor energy level is below the Fermi level, thereby increasing the ionization rate of the P-type dopant acceptor at the cross section and thus increasing the hole concentration. Furthermore, the AlN sublayer with high Al composition is used near the active region, which can raise the energy band, limit the electron overflow in the active region, and reduce the non-radiative recombination of electrons and holes in the non-recombination region, thereby improving the luminous efficiency of the device.

[0019] (2) The present invention provides that a small amount of larger diameter In atoms are doped into the P-type InAlGaN sublayer, which can reduce the lattice mismatch between the P-type InAlGaN sublayer and the U-type capping layer, and improve the effective P-type doping of the P-type electron blocking layer, thereby increasing the injection of holes and thus improving the luminescence efficiency.

[0020] (3) The P-type InAlGaN sublayer of the present invention can be a multilayer P-type In with varying Al composition. x Al y Ga 1-x-y A composite structure with N sublayers stacked sequentially can also be achieved using a multilayered P-type In structure with a constant Al composition. x Al y Ga 1-x-y P-type In with N-sublayer or multilayer Al composition variation x Al y Ga 1-x-y A superlattice structure with alternating N sublayers can also be used, or a P-type In structure with a constant composition can be employed in single-layer / multi-layer Al formations. x Al y Ga 1-x-yP-type In with variations in N-sublayer and monolayer / multilayer Al composition x Al y Ga 1-x-y The superlattice structure with alternating N-type sublayers can not only achieve a good electron blocking effect and obtain a high radiative recombination efficiency, but also alleviate the lattice compatibility between the P-type InAlGaN sublayer and the U-type capping layer.

[0021] (4) The present invention uses a P-type electron blocking layer composed of AlN sublayer and P-type InAlGaN sublayer stacked in sequence, which not only improves the crystal quality of the material and improves the radiative recombination in the active region of the LD device, but also improves the output optical power, aging lifetime, threshold current and skew efficiency of the LD device.

[0022] (5) The P-type In with Al composition variation of the present invention x Al y Ga 1-x-y The Al composition of the N sublayer can be gradually decreased, gradually increased and then gradually decreased, or gradient decreased, or gradient increased and then gradient decreased, by increasing the Al composition of each P-type In. x Al y Ga 1-x-y The Al content on the side of the N-sublayer closest to the active region can raise the energy band, further restricting electron overflow in the active region and reducing non-radiative recombination of electrons into the P-type layer with holes, thereby improving the luminous efficiency of the device.

[0023] (6) The P-type contact layer of the present invention uses P-type In a Al b Ga 1-a-b The N-layer can form a better ohmic contact with the P-electrode, further reducing the ohmic contact resistance, increasing the current spread of the P-type layer, and reducing the resistance of the device, thereby reducing the heat loss and lifespan of the LD device. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the epitaxial structure of a GaN-based blue laser provided in an embodiment of the present invention;

[0026] Figure 2 A schematic diagram illustrating one embodiment of the P-type electron blocking layer provided in this invention;

[0027] Figure 3 A schematic diagram illustrating another embodiment of the P-type electron blocking layer provided in this invention;

[0028] Figure 4 This is a schematic diagram of a p-type InAlGaN sublayer provided in an embodiment of the present invention, wherein (a) indicates that the p-type InAlGaN sublayer is a p-type In with constant Al composition. x Al y Ga 1-x-y The N-type In sublayer and Al composition decrease linearly and gradually. x Al y Ga 1-x-y (b) shows a superlattice structure with alternating N sublayers, where the P-type InAlGaN sublayers have a constant Al composition and are P-type In. x Al y Ga 1-x-y The N-type In sublayer and Al composition increase linearly and gradually. x Al y Ga 1-x-y (c) A superlattice structure with alternating N sublayers, where the P-type InAlGaN sublayer has a constant Al composition and is composed of P-type In. x Al y Ga 1-x-y The N-type In sublayer exhibits a linearly gradual increase followed by a linearly gradual decrease in Al composition. x Al y Ga 1-x-y A superlattice structure with alternating N sublayers, (d) P-type InAlGaN sublayers with constant Al composition and P-type In x Al y Ga 1-x-y The N-type In sublayer exhibits a linearly gradual decrease followed by a linearly gradual increase in Al composition. x Al y Ga 1-x-y A superlattice structure with alternating N-sublayers;

[0029] Figure 5 P-type In with Al composition variation provided in embodiments of the present invention x Al y Ga 1-x-y A schematic diagram of the Al composition variation in the N sublayer, where (a) represents a linearly gradual decrease in Al composition, (b) represents a linearly gradual increase in Al composition followed by a linearly gradual decrease, (c) represents a gradient decrease in Al composition, and (d) represents a gradient increase in Al composition followed by a gradient decrease.

[0030] In the figure: 1. Substrate; 2. N-type GaN layer; 3. N-type lower confinement layer; 4. N-type lower waveguide layer; 5. Active region; 6. Upper waveguide layer; 7. U-type capping layer; 8. P-type electron blocking layer; 81. AlN sublayer; 82. P-type InAlGaN sublayer; 9. P-type upper confinement layer; 10. P-type contact layer. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0034] like Figure 1As shown, this embodiment provides a GaN-based blue laser epitaxial structure, including a substrate 1, on which an N-type GaN layer 2, an N-type lower confinement layer 3, an N-type lower waveguide layer 4, an active region 5, an upper waveguide layer 6, a U-shaped cover layer 7, a P-type electron blocking layer 8, a P-type upper confinement layer 9, and a P-type contact layer 10 are sequentially stacked; the P-type electron blocking layer 8 includes an AlN sub-layer 81 and a P-type InAlGaN sub-layer 82 stacked in sequence. The P-type electron blocking layer 8 of this embodiment is formed by sequentially stacking and compounding the AlN sub-layer 81 and the P-type InAlGaN sub-layer 82. By utilizing the piezopolarization and spontaneous polarization of the P-type InAlGaN sub-layer 82 to cause a large bending of the energy band at the heterointerface, the acceptor energy level of the P-type dopant is below the Fermi level, improving the ionization rate of the P-type dopant acceptor at the cross-section, thereby increasing the hole concentration; and an AlN sub-layer 81 with a high Al component is used on the side close to the active region 5 to raise the energy band, limit the electron overflow of the active region 5, and reduce the non-radiative recombination of electrons and holes in the non-recombination region, thereby improving the light emission efficiency of the device; at the same time, by doping a small amount of In atoms with a larger diameter in the P-type InAlGaN sub-layer 82, on the one hand, it can reduce the lattice mismatch between the P-type InAlGaN sub-layer 82 and the U-shaped cover layer 7, and on the other hand, it can improve the effective P-type doping of the P-type electron blocking layer 8, enhance the hole injection, and thus improve the light emission efficiency.

[0035] In some embodiments, the P-type InAlGaN sub-layer 82 is a single-layer P-type In with a varying Al component x Al y Ga 1-x-y N sub-sub-layer, or the P-type InAlGaN sub-layer 82 is a composite structure in which multiple P-type In with varying Al components x Al y Ga 1-x-y N sub-sub-layers are sequentially stacked, as Figure 2 shown, where 0 ≤ x < y < 1 and 0 < x + y < 1. Among them, each layer of the multiple P-type In with varying Al components x Al y Ga 1-x-y N sub-sub-layers has a varying Al component, and the varying Al components of each layer can be the same or different.

[0036] In other embodiments, the P-type InAlGaN sub-layer 82 is a superlattice structure in which multiple P-type In with a constant Al component x Al y Ga 1-x-y N sub-sub-layers are cyclically stacked, as Figure 3 shown, or the P-type InAlGaN sub-layer 82 is a multiple P-type In with a varying Al component x Al y Ga1-x-y A superlattice structure with N sub - sub - layers stacked in a cyclic manner, where 0 ≤ x < y < 1, 0 ≤ y < 1, and 0 < x + y < 1. Among them, when the P - type InAlGaN sub - layer 82 is a superlattice structure with multiple P - type In x Al y Ga 1-x-y N sub - sub - layers with a constant Al composition stacked in a cyclic manner, the multiple P - type In x Al y Ga 1-x-y N sub - sub - layers form one period of the superlattice structure, and there are n periods in total, 0 < n < 50, and in one period, the Al composition of each In x Al y Ga 1-x-y N sub - sub - layer is constant, and the Al compositions of different P - type In x Al y Ga 1-x-y N sub - sub - layers with a constant Al composition can be different; when the P - type InAlGaN sub - layer 82 is a superlattice structure with multiple P - type In x Al y Ga 1-x-y N sub - sub - layers with a varying Al composition stacked in a cyclic manner, the multiple P - type In x Al y Ga 1-x-y N sub - sub - layers form one period of the superlattice structure, and there are n periods in total, 0 < n < 50, and in one period, the Al composition of each In x Al y Ga 1-x-y N sub - sub - layer varies, and the Al composition variations of different P - type In x Al y Ga 1-x-y N sub - sub - layers are different.

[0037] In some other embodiments, the P - type InAlGaN sub - layer 82 is a superlattice structure with single / multiple P - type In x Al y Ga 1-x-y N sub - sub - layers alternatingly stacked with single / multiple P - type In x Al y Ga 1-x-y N sub - sub - layers, as Figure 4 shown, where 0 ≤ x < y < 1, 0 < x + y < 1. When the P - type In x Al y Ga 1-x-y N sub - sub - layers with a constant Al composition are alternatingly stacked with single / multiple P - type In x Aly Ga 1-x-y When a period of the superlattice structure is composed of n sublayers of N, where 0 < n < 50, and the multi-layer P-type In with a constant Al composition x Al y Ga 1-x-y In each P-type In sublayer of N x Al y Ga 1-x-y The Al composition of the N sublayer is constant, and different P-type In with a constant Al composition x Al y Ga 1-x-y The Al composition of the N sublayer is different, and the multi-layer P-type In with a varying Al composition x Al y Ga 1-x-y In each P-type In sublayer of N x Al y Ga 1-x-y The Al composition of the N sublayer varies, and different P-type In with a varying Al composition x Al y Ga [[ID=3……此处原文似乎不完整,你可以检查一下并补充完整以便我继续准确翻译。 1-x-y The Al composition of the N sublayer varies differently; similarly, when a single / multi-layer P-type In with a constant Al composition x Al y Ga 1-x-y The N sublayer and the multi-layer P-type In with a varying Al composition x Al y Ga 1-x-y When a period of the superlattice structure is composed of n sublayers of N, where 0 < n < 50, and the multi-layer P-type In with a constant Al composition x Al y Ga 1-x-y In each P-type In sublayer of N x Al y Ga 1-x-y The Al composition of the N sublayer is constant, and different P-type In with a constant Al composition x Al y Ga 1-x-y The Al composition of the N sublayer is different, and the multi-layer P-type In with a varying Al composition x Al y Ga 1-x-y In each P-type In sublayer of N x Al y Ga 1-x-y The Al composition of the N sublayer varies, and different P-type In with a varying Al composition x Al y Ga 1-x-y The Al composition of the N sublayer varies differently.

[0038] In this embodiment, the P-type InAlGaN sublayer 82 can be made of multiple layers of P-type In with varying Al composition. x Al y Ga 1-x-y A composite structure with N sublayers stacked sequentially can also be achieved using a multilayered P-type In structure with a constant Al composition. x Al y Ga 1-x-y P-type In with N-sublayer or multilayer Al composition variation x Al y Ga 1-x-y A superlattice structure with alternating N sublayers can also be used, or a P-type In structure with a constant composition can be employed in single-layer / multi-layer Al formations. x Al y Ga 1-x-y P-type In with variations in N-sublayer and monolayer / multilayer Al composition x Al y Ga 1-x-y The superlattice structure with alternating N-type sublayers not only provides a good electron blocking effect and achieves high radiative recombination efficiency, but also improves the lattice fit between the P-type InAlGaN sublayer 82 and the U-type capping layer 7.

[0039] In some embodiments, the Al component varies with P-type In x Al y Ga 1-x-y The Al composition of the N sublayer exhibits a linearly gradual decrease, linearly gradual increase, linearly gradual increase followed by a linearly gradual decrease, linearly gradual decrease followed by a linearly gradual increase, gradient increase, gradient decrease, gradient decrease followed by a gradient increase, or gradient increase followed by a gradient decrease, etc., along its thickness direction. Figure 5 As shown. By increasing the value of each P-type In x Al y Ga 1-x-y The Al content on the side of the N-sublayer closest to the active region 5 can raise the energy band, further restricting electron overflow in the active region 5 and reducing the non-radiative recombination of electrons into the P-type layer with holes, thereby improving the luminous efficiency of the device.

[0040] When the P-type InAlGaN sublayer 82 is a multilayer Al composition variation P-type In x Al y Ga 1-x-y When N-sublayers are stacked sequentially in a composite structure, the P-type In with varying Al composition in multiple layers... x Al y Ga 1-x-y The Al composition variations in the N sublayers can be the same or different, and the Al composition variations in each layer are similar to those in the P-type In sublayers. x Al y Ga1-x-y The Al composition of the N sublayer can be linearly decreasing, linearly increasing, linearly increasing again, linearly decreasing again, linearly decreasing again, linearly increasing again, gradient increasing, gradient decreasing, gradient decreasing again, or gradient increasing again and gradient decreasing again along its thickness direction.

[0041] When the p-type InAlGaN sublayer 82 is a multilayer P-type In with constant Al composition x Al y Ga 1-x-y In a superlattice structure with alternating N-sublayers, the P-type In with constant multilayer Al composition... x Al y Ga 1-x-y N sublayers constitute one period of a superlattice structure, and a period of multilayer Al-composed P-type In x Al y Ga 1-x-y The Al composition of the N sublayer exhibits a linear gradient decrease, linear gradient increase, linear gradient increase, linear gradient decrease, linear gradient decrease, linear gradient increase, gradient increase, gradient decrease, gradient decrease, gradient increase, or gradient increase and gradient decrease along its thickness direction.

[0042] When the P-type InAlGaN sublayer 82 is a multilayer Al composition variation P-type In x Al y Ga 1-x-y In a superlattice structure with alternating N-sublayers, the P-type In with varying Al composition is... x Al y Ga 1-x-y One period of N sublayers forming a superlattice structure, and one period of multilayer Al composition variation of P-type In x Al y Ga 1-x-y The Al composition variations in the N sublayers can be the same or different, and the Al composition variations in each layer are similar to those in the P-type In sublayers. x Al y Ga 1-x-y The Al composition of the N sublayer can be linearly decreasing, linearly increasing, linearly increasing again, linearly decreasing again, linearly decreasing again, linearly increasing again, gradient increasing, gradient decreasing, gradient decreasing again, or gradient increasing again and gradient decreasing again along its thickness direction.

[0043] When the p-type InAlGaN sublayer 82 is a single-layer / multi-layer p-type In with constant Al composition x Al y Ga 1-x-y P-type In with variations in N-sublayer and monolayer / multilayer Al composition x Al yGa 1-x-y When the superlattice structure is formed by alternately stacking single / multiple sublayers of Al components with a constant P-type In x Al y Ga 1-x-y N sub-sublayers and single / multiple P-type In with varying Al components x Al y Ga 1-x-y N sub-sublayers form a period of the superlattice structure, and in a period, the P-type In with a constant Al component in multiple layers x Al y Ga 1-x-y The Al component of the N sub-sublayers gradually decreases linearly, increases linearly, increases linearly and then decreases linearly, decreases linearly and then increases linearly, increases in gradient, decreases in gradient, decreases in gradient and then increases in gradient, or increases in gradient and then decreases in gradient along its thickness direction, and / or the P-type In with varying Al components in multiple layers in a period x Al y Ga 1-x-y The Al component changes of the N sub-sublayers can be the same or different, and for each P-type In x Al y Ga 1-x-y The Al component of the N sub-sublayers is linearly decreasing, linearly increasing, increasing linearly and then decreasing linearly, decreasing linearly and then increasing linearly, increasing in gradient, decreasing in gradient, decreasing in gradient and then increasing in gradient, or increasing in gradient and then decreasing in gradient along its thickness direction.

[0044] Furthermore, the thickness of the AlN sublayer 81 is d1, the thickness of the P-type InAlGaN sublayer 82 is d2, and 0 < d1 < d2 < 10 nm. The thickness of the P-type electron blocking layer 8 is 8 nm - 15 nm. [[ID=3⑥]]

[0045] In this embodiment, in the P-type InAlGaN sublayer 82, each P-type In x Al y Ga 1-x-y N sub-sublayers can have the same or different thicknesses, and for each P-type In x Al y Ga 1-x-y The growth temperature, pressure, and atmosphere of the N sub-sublayers can be the same or different. I

[0046] In this embodiment, each P-type In x Al y Ga 1-x-y N sub-sublayers can contain In or not. Optimally, 0 ≤ x < y < 1, 0 ≤ x + y < 1, 0 < y < 0.5, 0 ≤ x < 0.1.

[0047] Furthermore, the U-shaped covering layer 7 is a U-shaped GaN layer, and the growth temperature of the U-shaped GaN layer is lower than that of the P-type electron blocking layer 8. By providing a U-shaped covering layer 7 (undoped covering layer) between the upper waveguide layer 6 and the P-type electron blocking layer 8, the upper waveguide layer 6 and the active region 5 can be protected; furthermore, the thickness of the U-shaped covering layer 7 is 100 - 200 nm.

[0048] In some embodiments, the P-type contact layer 10 is a P-type In a Al b Ga 1-a-b N layer, where 0 ≤ a < 1, 0 ≤ b < 1, and 0 ≤ a + b < 1. The P-type contact layer 10 can adopt an InGaN ternary compound or an InAlGaN quaternary compound. Both the InGaN ternary compound and the InAlGaN quaternary compound can form a better ohmic contact with the P electrode layer (ITO), further reducing the ohmic contact resistance, improving the current spreading of the P-type layer, reducing the resistance of the device, and thus reducing the thermal loss and extending the service life of the LD device.

[0049] Furthermore, the thickness of the P-type In a Al b Ga 1-a-b N layer is d3, where 0 < d3 < 50 nm; the doping concentration of the P-type In a Al b Ga 1-a-b N layer is 1×10 20 -1×10 21 cm -3 . There are mainly two methods for fabricating the P-type ohmic contact. One is to form an ohmic contact using a high work function metal and the P-type contact layer 10, and the other is to heavily dope the P-type contact layer 10 to make the potential barrier region where the metal contacts the P-type contact layer 10 thinner, and reduce the contact resistance through carrier tunneling. The conventional P-type contact layer 10 uses a P-type GaN layer. Since there is a lack of a metal with a work function greater than that of the P-type GaN layer (the work function is about 6.12 eV), in this embodiment, a P-type contact layer 10 doped with a heavily doped P-type dopant is used to increase the hole concentration and achieve a good ohmic contact. Also, because the work function of P-type InGaN is lower than that of P-type GaN, the ohmic contact resistance can be further reduced by growing a P-type InGaN contact layer, and a P-type InAlGaN contact layer doped with a small amount of Al component can also achieve the effect of reducing the ohmic contact resistance.

[0050] In some embodiments, the N-type lower confinement layer 3 includes a first N-type lower confinement layer, an N-type stress release layer, and a second N-type lower confinement layer, which are sequentially disposed on the N-type GaN layer 2. In this embodiment, an N-type stress release layer is inserted in the middle of the N-type lower confinement layer 3 to reduce the stress accumulated during the growth extending from bottom to top, thereby reducing the generation of edge cracks and providing a better crystal quality basis for the growth of subsequent epitaxial layers.

[0051] In some embodiments, the P-type upper confinement layer 9 is a P-type AlGaN layer, or may be composed of at least one U-shaped GaN sub-layer and multiple P-type In e Al f Ga 1-e-f AlGaN sub-layers stacked and compounded, where 0 ≤ e < f < 1, 0 < e < 1, and 0 < e + f < 1. In this embodiment, by doping an appropriate amount of In atoms with a larger radius in the P-type In e Al f Ga 1-e-f AlGaN sub-layer of the P-type upper confinement layer 9, the effective P-type doping of the P-type upper confinement layer 9 can be improved, the injection of holes can be increased, and thus the effective radiative recombination of electrons and holes in the light-emitting region can be improved, achieving the purpose of improving the light-emitting efficiency. By adding a U-shaped GaN sub-layer (undoped GaN sub-layer) to the P-type upper confinement layer 9, on the one hand, the current spreading ability of the P-type upper confinement layer 9 can be improved, the operating voltage of the LD device can be reduced, thereby reducing the thermal loss of the LD device and improving the service life of the device. On the other hand, the P-type doping degree can be reduced, thereby reducing the absorption loss of light by the P-type dopant, improving the light output efficiency. The U-shaped GaN sub-layer can also absorb Al / Mg atoms in the cavity parasitic reaction, reduce the defects generated by parasitic reaction atoms, improve the crystal quality of the epitaxial wafer, reduce the damage of the traditional P-type upper confinement layer in the high-temperature region to the light-emitting region, and reduce the increase in non-radiative recombination in the light-emitting region caused by the generation of epitaxial dark spots, which affects the effective radiative recombination in the light-emitting region. Using at least one U-shaped GaN sub-layer and multiple P-type In e Al f Ga 1-e-f AlGaN sub-layers stacked and compounded to form the P-type upper confinement layer 9 not only improves the crystal quality of the material, improves the radiative recombination in the active region of the LD device, but also enhances the performance of the LD device such as output optical power, aging life, threshold current, and slope efficiency.

[0052] Furthermore, when the P-type upper confinement layer 9 is composed of at least one U-shaped GaN sub-layer and multiple P-type In e Al f Ga 1-e-f AlGaN sub-layers stacked and compounded, there are specifically three implementation manners as follows: The first implementation manner is that the P-type upper confinement layer 9 is composed of one U-shaped GaN sub-layer and multiple P-type In with varying Al components e Alf Ga 1-e-f The N sub-layers are stacked and compounded in sequence, where 0 ≤ e < 0.01, 0 < f < 0.2, 0 < e + f < 1; in the second embodiment, the P-type upper confinement layer 9 is a U-shaped GaN sub-layer and one or more P-type In e Al f Ga 1-e-f N sub-layers are alternately stacked and compounded; in the third embodiment, the P-type upper confinement layer 9 is composed of a U-shaped GaN sub-layer and P-type In e Al f Ga 1-e-f N sub-layers are alternately stacked and compounded, where 0 ≤ e < 0.01, 0 < f < 0.2, 0 < e + f < 1, and the U-shaped GaN sub-layer and the P-type In e Al f Ga 1-e-f N sub-layers are one period, and the alternating growth period is n, 0 < n < 50.

[0053] Furthermore, in the P-type upper confinement layer 9, the Al component of the multiple P-type In e Al f Ga 1-e-f N sub-layers increases linearly and gradually, decreases linearly and gradually, increases in gradient, decreases in gradient, increases linearly and gradually and then decreases linearly and gradually, or increases in gradient and then decreases in gradient.

[0054] Furthermore, in the P-type upper confinement layer 9, the P-type doping concentrations of all the P-type In e Al f Ga 1-e-f N sub-layers are the same; or the P-type doping concentrations of all the P-type In e Al f Ga 1-e-f N sub-layers increase in gradient from the P-type electron blocking layer to the P-type contact layer; or the first few layers of the P-type In e Al f Ga 1-e-f N sub-layers near the active region are not doped or lightly doped with P-type dopants, and the P-type In e Al f Ga 1-e-f N sub-layers near the P-type contact layer are highly doped with P-type dopants.

[0055] Furthermore, the growth temperature of the U-shaped GaN sub-layer is T1, and the P-type In e Al f Ga 1-e-fThe growth temperature of the N sub-layer is T2, where 0 < T1 - T2 < 50. By appropriately increasing the temperature during the growth of the U-shaped GaN sub-layer, the migration rate of Mg and Al atoms staying at the atomic steps due to parasitic reactions can be increased, enabling them to be better incorporated and improving the crystal quality of the epitaxial layer, thereby obtaining an epitaxial wafer with higher crystal quality.

[0056] This embodiment also provides a method for preparing a GaN-based blue laser epitaxial structure according to any one of the above, including the following steps:

[0057] S1. Epitaxially grow an N-type GaN layer 2, an N-type lower confinement layer 3, an N-type lower waveguide layer 4, an active region 5, an upper waveguide layer 6, and a U-shaped cover layer 7 on a substrate 1 in sequence;

[0058] S2. Stack and grow an AlN sub-layer 81 and a P-type InAlGaN sub-layer 82 on the U-shaped cover layer 7 in sequence to form a P-type electron blocking layer 8;

[0059] S3. Epitaxially grow a P-type upper confinement layer 9 and a P-type contact layer 10 on the P-type electron blocking layer 8.

[0060] In some embodiments, the specific growth method of the P-type electron blocking layer 8 is: first grow a layer of AlN sub-layer 81 on the U-shaped cover layer 7, and then grow a single-layer P-type In x Al y —— 这里原文可能有误,推测是想表达Al,所以翻译为Al Ga 1-x-y N sub-sub-layer or stack and grow multiple layers of P-type In x Al y Ga 1-x-y N sub-sub-layers to form the P-type electron blocking layer 8.

[0061] In some other embodiments, the specific growth method of the P-type electron blocking layer 8 is: first grow a layer of AlN sub-layer 81 on the U-shaped cover layer, and then use a single-layer / multiple-layers of P-type In x Al y Ga 1-x-y N sub-sub-layers with a constant Al composition or multiple layers of P-type In x Al y Ga 1-x-y N sub-sub-layers as a period, and alternately grow n periods to form the P-type electron blocking layer 8.

[0062] In still some other embodiments, the specific growth method of the P-type electron blocking layer 8 is: first grow a layer of AlN sub-layer 81 on the U-shaped cover layer 7, and then use a single-layer / multiple-layers of P-type In x Al y Ga 1-x-yP-type In with variations in N-sublayer and monolayer / multilayer Al composition x Al y Ga 1-x-y The N-sublayer is a cycle, and n cycles are alternately grown to form a P-type electron blocking layer.

[0063] In the above embodiments, the crystal quality of the epitaxial layer can be improved by growing the P-type InAlGaN sublayer 82 through multi-layer sequential stacking or superlattice growth.

[0064] Furthermore, a P-type In superlattice structure with a constant Al composition in each period was grown using a variable-temperature method. x Al y Ga 1-x-y P-type In with changes in N sublayer or Al composition x Al y Ga 1-x-y The N-sublayer can improve the crystal growth quality of the P-type electron blocking layer 8, thereby improving the crystal quality of the subsequently grown P-type upper confinement layer 9 and P-type contact layer 10.

[0065] Furthermore, the thickness of the N-type GaN layer 2 is 1.0-3.0 μm, and the N-type doping concentration is 1 × 10⁻⁶. 18 cm -3 -1×10 20 cm -3 .

[0066] Furthermore, the total thickness of the N-type lower confinement layer 3 is 2-4 μm, and the first N-type lower confinement layer is an AlGaN layer with a thickness of 1.0-2.5 μm, grown at a temperature of 1100℃ and a pressure of 100 torr, with an N-type doping concentration of 1×10⁻⁶. 18 cm -3 -5×10 19 cm -3 The N-type stress relief layer is an InGaN layer with a thickness of 0.05-1.0 μm, a growth temperature of 980℃, a pressure of 200 torr, and an N-type doping concentration of 1×10⁻⁶. 18 cm -3 -5×10 19 cm -3 The second N-type lower confinement layer is an AlGaN layer with a thickness of 0.2-2.0 μm, grown at a temperature of 1100℃ and a pressure of 100 torr, with an N-type doping concentration of 1×10⁻⁶. 18 cm -3 -1×10 19 cm -3 .

[0067] Furthermore, the N-type lower waveguide layer 4 is an AlGaN layer with a growth thickness of 50-1000 nm and an N-type doping concentration of 1×10⁻⁶. 17 cm -3 -1×10 18 cm -3 .

[0068] Furthermore, the active region 55 includes alternating epitaxial quantum well layers and quantum barrier layers.

[0069] Furthermore, the U-shaped capping layer 77 is an undoped GaN layer with a thickness of 100-200 nm.

[0070] Furthermore, the P-type upper confinement layer 9 employs at least one U-type GaN sublayer and multiple P-type In layers. e Al f Ga 1-e-f The structure consists of stacked N-type sublayers with a thickness ranging from 10 nm to 700 nm and a P-type doping concentration of 5 × 10⁻⁶. 18 cm -3 -5×10 21 cm -3 .

[0071] In this embodiment, the substrate 1 can be any one of the following materials: sapphire, SiC, GaN, AlN, MgO, MgAl2O4, Si, ZnO, LiAlO2, LiGaO2, and GaAs. P-type doping can be achieved using Mg doping, and N-type doping can be achieved using Si doping.

[0072] The preparation method of the present invention will be described in detail below through a specific embodiment.

[0073] A method for fabricating a GaN-based blue laser epitaxial structure, using high-purity hydrogen (H2) or nitrogen (N2) as the carrier gas, and trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMAl), triethylgallium (TEGa), and ammonia (NH3) as Ga, In, Al, and N sources, respectively, and silane (SiH4) and magnesium pyrocene (Cp2Mg) as n-type and p-type dopant, respectively. The fabrication method includes the following steps:

[0074] 1) Heat GaN substrate 1 to 1100℃ and heat-treat the surface impurities and other residues for 5 minutes under pure hydrogen conditions, then introduce NH3 to stabilize for 6 minutes to repair the surface damaged by grinding and polishing. The heating and stabilization time can be long or short, and the optimal value is to match the growth of the epitaxial wafer.

[0075] 2) The temperature was raised to 1120℃, and NH3 and TMGa sources were introduced under a pressure of 200 torr. A 2µm thick N-type GaN layer was grown under a carrier gas mixture of hydrogen and nitrogen. The Si doping concentration was 5×10⁻⁶. 18 cm -3 ;

[0076] 3) An N-type lower confinement layer 3 is grown on the N-type GaN layer 2. The specific process is as follows:

[0077] First, an AlGaN layer with a thickness of 1.5 μm was grown at a temperature of 1100℃ and a pressure of 100 torr as the first N-type lower confinement layer. The Si doping concentration was 2.0 × 10⁻⁶. 18 cm -3 ;

[0078] Then, the temperature was lowered to 980℃, and a 200nm thick InGaN layer was grown as an N-type stress relief layer under a pure nitrogen atmosphere and a pressure of 200 torr. The Si doping concentration was 3.0 × 10⁻⁶. 18 cm -3 ;

[0079] The temperature was then increased to 1100℃, and a 900nm thick AlGaN layer was deposited under a pressure of 100 torr as the second N-type lower confinement layer. The Si doping concentration was 2.0 × 10⁻⁶. 18 cm -3 The growth of the N-type lower confinement layer 3 was completed;

[0080] 4) Cool to 980℃ and grow a 200nm thick InGaN layer as the N-type lower waveguide layer 4 under a pure nitrogen atmosphere and a pressure of 200 torr. The Si doping concentration is 3.5×10⁻⁶. 17 cm -3 ;

[0081] 5) Next, a quantum well layer and a quantum barrier layer are grown. First, the quantum barrier layer is grown at a growth temperature of 940℃, a growth pressure of 200 torr, and an atmosphere of nitrogen and hydrogen mixed gas. The thickness of the GaN barrier layer is 3.0 nm. The thickness of the InGaN quantum well layer is 2.5 nm, the growth temperature is 880℃, the growth pressure is the same as that of the quantum barrier layer, and the atmosphere is pure nitrogen. Then, a barrier layer LQB is grown. The LQB layer is composed of GaN layers with a thickness of 3 nm and a growth temperature of 940℃. The atmosphere of the LQB barrier layer is the same as that of the quantum barrier layer, forming the active region 5.

[0082] 6) Next, a 150 nm thick InGaN layer is grown at 980 °C, in a pure nitrogen atmosphere, and at a pressure of 200 torr as the upper waveguide layer 6.

[0083] 7) Under the same conditions, a 150 nm thick undoped GaN layer is grown on the upper waveguide layer 6 as a U-shaped capping layer 7 to protect the upper waveguide layer 6 and the active region 5.

[0084] 8) Grow an 8nm-15nm thick P-type electron blocking layer 8 on the U-shaped capping layer 7. The specific process can be any one of the following four implementation methods:

[0085] The first implementation method involves growing a 1-2 nm AlN layer on the U-shaped capping layer 7 under the following conditions: a growth temperature of 1040℃, a pressure of 100 torr, and a pure hydrogen atmosphere; then, under the same conditions, growing an Al layer with an Al composition of 24% and a thickness of 1.5 nm. 0.24 Ga 0.76 N layer, Al 0.24 Ga 0.76 The N-layer is undoped with Mg; then, a 1.5 nm thick InGaN layer is grown under pure nitrogen atmosphere, pressure of 200 torr, and temperature of 1040 °C, with Mg doping of 1 × 10⁻⁶. 19 cm -3 -5×10 19 cm -3 Al 0.24 Ga 0.76 The N-layer and the InGaN-layer constitute one cycle, which is repeated for 4 cycles.

[0086] The second implementation method involves first growing a 1-2 nm AlN layer on the U-shaped capping layer 7 under growth conditions of 1020℃, 100 torr, and a pure hydrogen atmosphere; then, under the same conditions, growing a P-type In layer with an Al composition that linearly decreases from 42% to 0 and a thickness of 8 nm. x Al y Ga 1-x-y N sublayer, Mg doping level 2×10 19 cm -3 -5×10 19 cm -3 ;

[0087] The third implementation method: First, an AlN layer of 1-2 nm is grown on the U-shaped capping layer 7 under the conditions of growth temperature of 1020℃, pressure of 100 torr, and pure hydrogen atmosphere; then, an In layer with an Al composition of 42% and a thickness of 2-5 nm is grown under the same temperature and pure nitrogen atmosphere. 0.04 Al 0.42 Ga 0.54 N-layer, Mg doped to 2×10⁻⁶ 19 cm -3 Next, under the same temperature and atmosphere conditions, the Al and In flow rates were reduced to grow an In layer with a thickness of 2-5 nm. 0.02 Al0.24 Ga 0.74 N-layer, Mg doped to 2×10⁻⁶ 19 cm -3 Subsequently, the Al and In flow rates were reduced, and In layers with a thickness of 2-5 nm were grown at a temperature of 1020℃. 0.01 Al 0.12 Ga 0.83 N-layer, Mg doped to 2×10⁻⁶ 19 cm -3 ;

[0088] The fourth implementation method: First, an AlN layer of 1-2 nm is grown on the U-shaped capping layer 7 under the conditions of growth temperature of 1020℃, pressure of 100 torr, and pure hydrogen atmosphere; then, an In layer with an Al composition of 22% and a thickness of 2 nm is grown under the same conditions. 0.04 Al 0.22 Ga 0.74 N-layer, Mg doped to 5×10⁻⁶ 19 cm -3 Then, under the same temperature and atmosphere conditions, In with the same composition was grown to a thickness of 2-5 nm. 0.04 Al 0.22 Ga 0.74 N-layer, Mg doped to 3×10⁻⁶ 19 cm -3 Growth; followed by the re-growth of In with an Al composition of 2-5 nm thickness under the same temperature and atmosphere conditions. 0.02 Al 0.12 Ga 0.86 N-layer, Mg doped to 1×10⁻⁶ 19 cm -3 ;

[0089] 9) Cool down to 980℃ and grow a 300nm thick P-type AlGaN layer on the P-type electron blocking layer 8 as the P-type upper confinement layer 9. The Mg doping concentration is 5×10⁻⁶. 19 cm -3 ;

[0090] 10) Finally, cool to 920℃ to grow a 10nm thick P-type InAlGaN layer or a P-type InGaN layer as the P-type contact layer. The Mg doping concentration is 1×10⁻⁶. 20 -1×10 21 cm -3 .

[0091] The epitaxial equipment described above is metal-organic chemical vapor deposition, but it is not limited to this. After epitaxial growth is completed, the grown epitaxial wafer is subjected to semiconductor processing techniques such as cleaning, deposition, photolithography, and etching to produce a single chip.

[0092] The above description is only a preferred embodiment of the present invention and is 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 within the protection scope of the present invention.

Claims

1. A GaN-based blue laser epitaxial structure, comprising a substrate, characterized in that: The substrate is provided with, in sequence, an N-type GaN layer, an N-type lower confinement layer, an N-type lower waveguide layer, an active region, an upper waveguide layer, a U-type capping layer, a P-type electron blocking layer, a P-type upper confinement layer, and a P-type contact layer; the P-type electron blocking layer comprises, in sequence, an AlN sublayer and a P-type InAlGaN sublayer; the P-type InAlGaN sublayer is any one of the following structures: a) The P-type InAlGaN sublayer is a monolayer of P-type In with varying Al composition. x Al y Ga 1-x-y N-type sublayers, or the P-type InAlGaN sublayers being multilayered P-type In with varying Al composition. x Al y Ga 1-x-y A composite structure in which N sub-layers are stacked sequentially, where 0≤x <y<1,0<x+y<1; b) The P-type InAlGaN sublayer is a multilayer P-type In with constant Al composition. x Al y Ga 1-x-y The superlattice structure of cyclically stacked N-type sublayers, or the P-type InAlGaN sublayers being multilayered P-type In with varying Al composition. x Al y Ga 1-x-y A superlattice structure with N-sublayer cyclic stacking, where 0≤x <y<1,0≤y<1,0<x+y<1; c) The P-type InAlGaN sublayer is a single-layer / multi-layer P-type In with constant Al composition. x Al y Ga 1-x-y P-type In with variations in N-sublayer and monolayer / multilayer Al composition x Al y Ga 1-x-y A superlattice structure with alternating N-sublayers, where 0 ≤ x <y<1,0<x+y<1。 2. The GaN-based blue laser epitaxial structure as described in claim 1, characterized in that: The P-type In with changes in Al composition x Al y Ga 1-x-y The Al composition of the N sublayer is linearly decreasing, linearly increasing, linearly increasing again, linearly decreasing again, linearly decreasing again, linearly increasing again, gradient increasing, gradient decreasing, gradient decreasing again, or gradient increasing again and gradient decreasing.

3. The GaN-based blue laser epitaxial structure as described in claim 1, characterized in that: The thickness of the AlN sublayer is d1, and the P-type In x Al y Ga 1-x-y The thickness of the N-sublayer is d2, 0 <d1<d2<10nm。 4. The GaN-based blue laser epitaxial structure as described in claim 1, characterized in that: The U-shaped capping layer is a U-shaped GaN layer, and the growth temperature of the U-shaped GaN layer is lower than that of the P-shaped electron blocking layer.

5. The GaN-based blue laser epitaxial structure as described in claim 1, characterized in that: The P-type contact layer is a P-type In a Al b Ga 1-a-b There are N layers, where 0 ≤ a < 1, 0 ≤ b < 1, and 0 ≤ a + b < 1.

6. The GaN-based blue laser epitaxial structure as described in claim 1, characterized in that: The N-type lower confinement layer includes a first N-type lower confinement layer, an N-type stress relief layer, and a second N-type lower confinement layer, which are sequentially disposed on the N-type GaN layer.

7. A method for fabricating a GaN-based blue laser epitaxial structure according to any one of claims 1-6, characterized in that, Includes the following steps: S1. An N-type GaN layer, an N-type lower confinement layer, an N-type lower waveguide layer, an active region, an upper waveguide layer, and a U-type capping layer are epitaxially grown sequentially on the substrate. S2. AlN sublayers and P-type InAlGaN sublayers are sequentially stacked on the U-shaped capping layer to form a P-type electron blocking layer. S3. Epitaxially grow a P-type upper confinement layer and a P-type contact layer on the P-type electron blocking layer.

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