Laser with electronically expanded structure and method for growing the same

Abstract

The application discloses a laser with an electron extension structure and a growth method thereof. The laser with the electron extension structure comprises an n-type confinement layer, a first waveguide layer, a light-emitting layer, a second waveguide layer, a p-type confinement layer and a p-type ohmic contact layer arranged in sequence along a specified direction; the laser structure further comprises an n-type electron extension layer arranged between the n-type confinement layer and the first waveguide layer, and the potential barrier of the n-type electron extension layer is higher than that of any one of the n-type confinement layer and the first waveguide layer, so that the electrons moving from the n-type confinement layer to the light-emitting layer are blocked by the n-type electron extension layer to reduce the moving speed. The manufacturing process of the GaN-based laser provided by the application is simple, good in repeatability, and is favorable for reducing the threshold voltage of the GaN-based laser, improving the light-emitting efficiency of the laser, achieving the effects of increasing the service life of the laser and the like, and is more suitable for industrialized production.

Description

Technical Field

[0001] This invention relates in particular to a laser with an electronically extended structure and its growth method, belonging to the field of semiconductor technology. Background Technology

[0002] Gallium nitride (GaN) lasers are a current research hotspot, attracting widespread attention and application as a next-generation optoelectronic device in fields such as novel displays, optical communications, and optical lighting. GaN lasers require high current densities to operate, placing extremely high demands on the crystal quality of the materials. Unlike other GaN devices, such as LEDs, which are not highly sensitive to crystal quality, poor material quality directly impacts the lifespan and output power of lasers. Existing epitaxial structures and methods still fall far short of the lifespan and performance of other lasers (GaAs-based).

[0003] Lasers inject electrons and holes into the laser structure in a direction perpendicular to the junction plane by applying an external bias voltage. Most of the charge carriers entering the emissive layer (active region) recombine and generate light. At the same time, a large portion of electrons overflow and rush into the P-type region, causing electron leakage and forming leakage current, which in turn affects the lifetime improvement of GaN-based lasers. Traditional methods generally use an electron blocking layer (EBL). The electron blocking layer (EBL) blocks electrons that cross the emissive layer and prevents them from entering the P-type upper confinement layer, thereby suppressing electron leakage current, increasing the electron concentration in the laser, reducing the laser's turn-on voltage, increasing the laser's optical output power, and effectively alleviating the laser's efficiency degradation problem. Summary of the Invention

[0004] The main objective of this invention is to provide a laser with an electronically extended structure and its growth method, thereby overcoming the shortcomings of the prior art.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] This invention provides a laser with an electron-spreading structure, comprising an n-type confinement layer, a first waveguide layer, a light-emitting layer, a second waveguide layer, a p-type confinement layer, and a p-type ohmic contact layer arranged sequentially along a specified direction; the laser structure further includes an n-type electron-spreading layer disposed between the n-type confinement layer and the first waveguide layer, wherein the potential barrier of the n-type electron-spreading layer is higher than the potential barrier of either the n-type confinement layer or the first waveguide layer, so that the movement speed of electrons moving from the n-type confinement layer to the light-emitting layer is reduced by the n-type electron-spreading layer.

[0007] Furthermore, both the n-type electron extension layer and the n-type confinement layer are formed of Al-containing group III nitrides, and the Al content in the n-type electron extension layer is greater than the Al content in the n-type confinement layer.

[0008] Furthermore, the Al component content in the n-type electron extension layer is 10-15 at.%, and the Al component content in the n-type confinement layer is 5-10 at.%.

[0009] Furthermore, the material of the n-type confinement layer includes AlGaN, and the n-type electron extension layer is a single-layer n-type AlGaN layer or an n-type AlGaN / GaN superlattice. The n-type AlGaN / GaN superlattice can achieve higher Al doping content, resulting in better blocking and extension effects for electrons.

[0010] Furthermore, the thickness of the n-type electron extension layer is 5-30 nm.

[0011] Furthermore, the thickness of the AlGaN layer in the n-type AlGaN / GaN superlattice is 1-5 nm, and the thickness of the GaN layer is 1-5 nm.

[0012] Furthermore, the doping concentration of the acceptor impurity in the n-type electron extension layer is lower than that in the n-type confinement layer. This is to prevent the electron migration velocity from decreasing too much. Specifically, the doping concentration of the acceptor impurity in the n-type electron extension layer is 1E17-1E18 cm⁻¹. -3 The doping concentration of the acceptor impurity in the n-type confinement layer is 1E18-5E18 cm⁻¹ -3 .

[0013] Furthermore, both the first waveguide layer and the second waveguide layer are made of undoped InGaN or GaN.

[0014] Furthermore, the light-emitting layer includes an InGaN / GaN quantum well light-emitting layer. When undoped InGaN is used as the material for the first waveguide layer and the second waveguide layer, the In content in the first waveguide layer and the second waveguide layer is lower than the In content in the light-emitting layer. The In content in the first waveguide layer, the second waveguide layer and the light-emitting layer is determined by the laser wavelength.

[0015] Furthermore, the p-type confinement layer is made of AlGaN, and the p-type ohmic contact layer is made of GaN.

[0016] Furthermore, the n-type confinement layer is disposed on a substrate, which is an n-type GaN homogeneous substrate or an n-type GaN template formed from a heterogeneous substrate.

[0017] Furthermore, the laser with the electronically extended structure comprises: an n-GaN substrate, an n-AlGaN confinement layer, an n-AlGaN or n-AlGaN / GaN superlattice electronically extended layer, a first InGaN waveguide layer, an InGaN / GaN quantum well light-emitting layer, a second InGaN waveguide layer, a p-AlGaN confinement layer, and a p-GaN ohmic contact layer arranged sequentially along a specified direction.

[0018] The present invention also provides a method for growing the laser with the electron extension structure, comprising growing an n-type confinement layer, an n-type electron extension layer, a first waveguide layer, a light-emitting layer, a second waveguide layer, a p-type confinement layer, and a p-type ohmic contact layer sequentially stacked along a specified direction.

[0019] Compared with the prior art, the advantages of the present invention include:

[0020] The present invention provides a GaN-based laser, which inserts an n-type AlGaN or AlGaN / GaN superlattice as an electron spreading layer after the n-type confinement layer and between the first waveguide layer, while removing the p-type electron blocking layer between the second waveguide layer and the p-type confinement layer. The electron spreading layer can slow down the high-speed electron flow in the N-type region during laser operation, and homogenize the electron distribution, reduce the probability of electrons crossing the active region, and improve the recombination probability and efficiency of electrons in the active region.

[0021] The present invention provides a GaN-based laser with a simple and repeatable fabrication process, which helps to reduce the threshold voltage of GaN-based lasers, improve the luminous efficiency of lasers, and increase the lifespan of lasers, making it more suitable for industrial production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a traditional GaN-based laser in the prior art;

[0023] Figure 2 This is a schematic diagram of a traditional GaN-based laser in the existing technology;

[0024] Figure 3 This is a schematic diagram of the structure of a GaN-based laser in a typical embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of a GaN-based laser in a typical embodiment of the present invention. Detailed Implementation

[0026] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate the technical solution, its implementation process, and its principles in conjunction with the accompanying drawings and specific embodiments.

[0027] This invention provides a GaN-based laser that replaces the p-type electron blocking layer between the second waveguide layer and the p-type confinement layer with an n-type AlGaN or AlGaN / GaN superlattice electron extension layer between the n-type confinement layer and the first waveguide layer. Simultaneously, this n-type AlGaN or AlGaN / GaN superlattice electron extension layer can slow down the high-speed electron flow in the N-type region during laser operation, homogenize the electron distribution, reduce the probability of electrons crossing the active region, and improve the recombination probability and efficiency of electrons in the active region. Ultimately, this overcomes the drawbacks of the p-type electron blocking layer, such as excessively high device voltage and insufficient Mg doping enhancement.

[0028] Please see Figure 3 A GaN-based laser includes an n-type substrate (or n-type bottom layer) 11, an n-type confinement layer (or lower confinement layer) 12, an n-type electron extension layer 13, a first waveguide layer (or lower waveguide layer) 14, a light-emitting layer (or active region, light-emitting active region, quantum well light-emitting layer, etc.) 15, a second waveguide layer (or upper waveguide layer) 16, a p-type confinement layer (or upper confinement layer) 17, and a p-type ohmic contact layer 18, stacked sequentially along a specified direction. The potential barrier of the n-type electron extension layer 13 is greater than the potential barrier of either the n-type confinement layer 12 or the first waveguide layer 14, so that electrons moving from the n-type confinement layer 12 to the light-emitting layer 15 are blocked by the n-type electron extension layer 13, thus reducing their movement speed.

[0029] It should be noted that the n-type substrate 11 and n-type confinement layer 12 can be regarded as the n-type region of the GaN-based laser, and the p-type confinement layer 17 and p-type ohmic contact layer 18 can be regarded as the p-type region of the GaN-based laser. The specified direction can be the longitudinal direction of the device, and the direction of the overall movement of electrons and holes can be parallel to the pointing direction.

[0030] Specifically, the n-type substrate 11 can be an n-GaN template of an n-GaN homo-substrate or a hetero-substrate.

[0031] Specifically, the n-type confinement layer 12 and the n-type electron extension layer 13 are formed of Al-containing group III nitrides, and the Al content in the n-type electron extension layer is greater than the Al content in the n-type confinement layer 12. More specifically, the Al content in the n-type electron extension layer 13 is 10-15 at.%, and the Al content in the n-type confinement layer 12 is 5-10 at.%.

[0032] Specifically, the n-type confinement layer 12 can be an n-AlGaN confinement layer, and the n-type electron extension layer 13 can be a single-layer n-type AlGaN layer or an n-type AlGaN / GaN superlattice.

[0033] Specifically, the thickness of the n-type electron extension layer is 5-30 nm. When the n-type electron extension layer 13 is a single-layer n-type AlGaN layer, the thickness of the n-type AlGaN layer is 5-30 nm. When the n-type electron extension layer 13 is an n-type AlGaN / GaN superlattice, the thickness of the AlGaN layer in the n-type AlGaN / GaN superlattice is 1-5 nm, and the thickness of the GaN layer is 1-5 nm.

[0034] Specifically, the growth conditions of the AlGaN / GaN superlattice or monolayer AlGaN layer include a high growth temperature of 1000-1100℃, a low growth pressure of 50-150 torr, and a low ratio of ammonia to MO source: V / III ratio of 10-100. Materials grown under these conditions have higher quality, no excess vacancies or defects, and are more conducive to electron expansion.

[0035] Specifically, the first waveguide layer 14 and the second waveguide layer 16 can both be undoped InGaN waveguide layers or GaN waveguide layers, and the light-emitting layer 15 can be an InGaN / GaN quantum well light-emitting layer. When an undoped InGaN layer is used as the material of the first waveguide layer and the second waveguide layer, the In content in the first waveguide layer and the second waveguide layer is lower than the In content in the light-emitting layer. The In content in the first waveguide layer, the second waveguide layer and the light-emitting layer is determined by the laser wavelength.

[0036] Specifically, the p-type confinement layer 17 can be a p-AlGaN confinement layer, and the p-type ohmic contact layer 18 can be a p-GaN ohmic contact layer.

[0037] For details, please refer to Figure 4 This invention addresses the fundamental problem of strong electrons and weak holes in existing GaN-based lasers by inserting an n-type AlGaN / GaN superlattice or an n-type AlGaN layer as an electron spreading layer 13 between the n-type confinement layer 12 and the first waveguide layer 14. Simultaneously, the p-type electron blocking layer located between the second waveguide layer 16 and the p-type confinement layer 17 is eliminated. After electrons are generated in the n-type region, they first pass through the high-barrier electron spreading layer 13, where they are blocked, reducing their migration speed and decreasing the possibility of electrons crossing the active region. Furthermore, in traditional GaN-based lasers, the high migration speed of electrons leads to a relatively concentrated electron distribution. Figure 4As can be seen, in the GaN-based laser provided by this invention, after electrons are blocked by the electron spreading layer, the concentration of the electron flow is disrupted, and the movement and distribution of electrons become more uniform. At the same time, since there is no electron blocking layer in the p-type region, the holes generated in the p-type region are no longer blocked in their flow to the active region, and their migration speed is accelerated. Thus, the electron operation mode is weakened while the hole operation mode is strengthened, thereby improving the fundamental problem of strong electrons and weak holes in traditional GaN-based lasers. This greatly enhances the probability of radiative recombination of electrons and holes in the active region, thereby reducing the leakage current and threshold voltage during lasing without using an electron blocking layer.

[0038] Example 1

[0039] Please see Figure 3 An epitaxial structure A of a GaN-based laser includes an n-GaN substrate, a Si-doped n-AlGaN confinement layer, a Si-doped n-AlGaN / GaN superlattice electronic extension layer, an undoped first InGaN waveguide layer, an InGaN / GaN quantum well light-emitting layer, an undoped second InGaN waveguide layer, a Mg-doped p-AlGaN confinement layer, and a Mg-doped p-GaN ohmic contact layer, arranged sequentially along a specified direction.

[0040] In this embodiment, the n-AlGaN confinement layer has a thickness of 850 nm and an Al content of 8 at.%; the n-AlGaN / GaN superlattice electronic extension layer comprises four periods of AlGaN / GaN superlattices, each AlGaN / GaN superlattice containing an AlGaN layer with a thickness of 3 nm, an Al content of 12 at.%, and a GaN layer with a thickness of 2 nm; the first InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the InGaN / GaN quantum well light-emitting layer comprises two periods of InGaN / GaN quantum wells, each InGaN / GaN quantum well containing an InGaN well layer with a thickness of 3 nm, an In content of 15 at.%, and a GaN barrier layer with a thickness of 7 nm; the second InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the p-AlGaN confinement layer has a thickness of 850 nm and an Al content of 5 at.%; and the p-GaN ohmic contact layer has a thickness of 10 nm.

[0041] Example 2

[0042] An epitaxial structure B of a GaN-based laser includes an n-GaN substrate, a Si-doped n-AlGaN confinement layer, a Si-doped n-AlGaN electron extension layer, an undoped first InGaN waveguide layer, an InGaN / GaN quantum well light-emitting layer, an undoped second InGaN waveguide layer, a Mg-doped p-AlGaN confinement layer, and a Mg-doped p-GaN ohmic contact layer, arranged sequentially along a specified direction.

[0043] In this embodiment, the n-AlGaN confinement layer has a thickness of 850 nm and an Al content of 8 at.%; the n-AlGaN electron extension layer has a thickness of 20 nm and an Al content of 12 at.%; the first InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the InGaN / GaN quantum well light-emitting layer comprises two periods of InGaN / GaN quantum wells, each InGaN / GaN quantum well having an In GaN well layer thickness of 3 nm and an In content of 15 at.%; and a GaN barrier layer thickness of 7 nm; the second InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the p-AlGaN confinement layer has a thickness of 850 nm and an Al content of 5 at.%; and the p-GaN ohmic contact layer has a thickness of 10 nm.

[0044] Comparative Example 1

[0045] An epitaxial structure C of a GaN-based laser includes an n-GaN substrate, a Si-doped n-AlGaN confinement layer, a Si-doped n-AlGaN / GaN superlattice electron extension layer, an undoped first InGaN waveguide layer, an InGaN / GaN quantum well light-emitting layer, an undoped second InGaN waveguide layer, a Mg-doped p-type AlGaN electron blocking layer, a Mg-doped p-AlGaN confinement layer, and a Mg-doped p-GaN ohmic contact layer, arranged sequentially along a specified direction.

[0046] In this embodiment, the n-AlGaN confinement layer has a thickness of 850 nm and an Al content of 8 at.%. The n-AlGaN / GaN superlattice electronic extension layer comprises four periods of AlGaN / GaN superlattices, each AlGaN / GaN superlattice containing an AlGaN layer with a thickness of 3 nm and an Al content of 12 at.%, and a GaN layer with a thickness of 2 nm. The first InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%. The InGaN / GaN quantum well light-emitting layer comprises two periods. The InGaN / GaN quantum wells have the following characteristics: the InGaN well layer has a thickness of 3 nm and an In content of 15 at.%, and the GaN barrier layer has a thickness of 7 nm; the second InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the p-type AlGaN electron blocking layer has a thickness of 20 nm and an Al content of 15 at.%; the p-AlGaN confinement layer has a thickness of 850 nm and an Al content of 5 at.%; and the p-GaN ohmic contact layer has a thickness of 10 nm.

[0047] Comparative Example 2

[0048] Please see Figure 1 An epitaxial structure D of a GaN-based laser includes an n-GaN substrate 21, an n-AlGaN confinement layer 22, an undoped first InGaN waveguide layer 23, an InGaN / GaN quantum well light-emitting layer (or active region) 24, an undoped second InGaN waveguide layer 25, a Mg-doped p-AlGaN electron blocking layer 26, a Mg-doped p-AlGaN confinement layer 27, and a Mg-highly doped p-GaN ohmic contact layer 28, stacked sequentially along a specified direction.

[0049] Specifically, the n-AlGaN confinement layer has a thickness of 850 nm and an Al content of 8 at.%; the first InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the InGaN / GaN quantum well light-emitting layer comprises two periods of InGaN / GaN quantum wells, each InGaN / GaN quantum well having an InGaN well layer thickness of 3 nm and an In content of 15 at.%; and a GaN barrier layer thickness of 7 nm; the second InGaN waveguide layer has a thickness of 60 nm and an In content of 3 at.%; the p-type AlGaN electron blocking layer has a thickness of 20 nm and an Al content of 15 at.%; the p-AlGaN confinement layer has a thickness of 850 nm and an Al content of 5 at.%; and the p-GaN ohmic contact layer has a thickness of 10 nm.

[0050] The principle of this GaN-based laser is as follows: Figure 2 As shown, majority carriers (electrons) are generated by an n-type GaN template on an n-type GaN homo- or hetero-type substrate and a Si-doped n-type AlGaN confinement layer. Minority carriers (holes) are mainly generated by a p-type AlGaN electron blocking layer, a p-type AlGaN confinement layer, and a p-type GaN layer. The p-type AlGaN electron blocking layer is thinner and has a higher Al content, which can block electrons overflowing from the self-emitting layer. Under the driving force of high current density, a large number of electrons with small effective mass and fast mobility rush from the bottom of the conduction band to the emitting layer, while holes with large effective mass and slow mobility flow from the top of the valence band to the emitting layer. Due to the mismatch between the behavior of electrons and holes, electron recombination in the emitting layer is insufficient, and a large number of electrons cross the emitting layer to reach the p-type AlGaN electron blocking layer and are annihilated there. Similarly, holes are blocked by the p-type AlGaN electron blocking layer during their journey, resulting in fewer holes reaching the emitting layer for recombination, which in turn leads to a decrease in radiative recombination efficiency.

[0051] Using the same chip fabrication process, the epitaxial structures of the GaN-based lasers in Examples 1, 2, Comparative Example 1, and Comparative Example 2 were fabricated to form GaN-based lasers. The obtained GaN-based lasers were then tested, and the test results are shown in Table 1.

[0052] Table 1 shows the performance characterization results of GaN-based lasers fabricated from epitaxial structures in Examples 1, 2, Comparative Example 1, and Comparative Example 2.

[0053]

[0054]

[0055] As can be seen from Table 1, the GaN-based laser provided by this invention significantly reduces the threshold voltage. Although the threshold current increases somewhat and there may still be electron overflow, the overall resistance of the GaN-based laser decreases, directly increasing its lifetime. Furthermore, due to the increased capture of electrons and holes in the active region, the efficiency of radiative recombination is also increased to some extent, which is reflected in the increase of lasing power of the GaN-based laser.

[0056] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A laser with an electronically extended structure, comprising an n-type confinement layer, a first waveguide layer, a light-emitting layer, a second waveguide layer, a p-type confinement layer, and a p-type ohmic contact layer arranged sequentially along a specified direction; characterized in that: The laser structure further includes an n-type electron spreading layer disposed between the n-type confinement layer and the first waveguide layer. Both the n-type electron spreading layer and the n-type confinement layer are formed of Al-containing group III nitrides, and the Al content in the n-type electron spreading layer is greater than the Al content in the n-type confinement layer. This results in the potential barrier of the n-type electron spreading layer being higher than the potential barrier of either the n-type confinement layer or the first waveguide layer. Consequently, the movement speed of electrons moving from the n-type confinement layer to the light-emitting layer is reduced by the n-type electron spreading layer. Furthermore, there is no p-type electron blocking layer between the second waveguide layer and the p-type confinement layer.

2. The laser with an electronically extended structure according to claim 1, characterized in that: The Al content in the n-type electron extension layer is 10 at.%-15 at.%, and the Al content in the n-type confinement layer is 5 at.%-10 at.%.

3. The laser with an electronically extended structure according to claim 1, characterized in that: The material of the n-type confinement layer includes AlGaN, and the n-type electron extension layer is a single-layer n-type AlGaN layer or an n-type AlGaN / GaN superlattice.

4. The laser with an electronically extended structure according to claim 3, characterized in that: The thickness of the n-type electron extension layer is 5nm-30nm.

5. The laser with an electronically extended structure according to claim 4, characterized in that: The thickness of the AlGaN layer in the n-type AlGaN / GaN superlattice is 1nm-5nm, and the thickness of the GaN layer is 1nm-5nm.

6. The laser with an electronically extended structure according to claim 1, characterized in that: The first waveguide layer and the second waveguide layer are both made of undoped InGaN or GaN.

7. The laser with an electronically extended structure according to claim 1, characterized in that: The light-emitting layer includes an InGaN / GaN quantum well light-emitting layer.

8. The laser with an electronically extended structure according to claim 1, characterized in that: The p-type confinement layer is made of AlGaN, and the p-type ohmic contact layer is made of GaN.

9. The laser with an electronically extended structure according to claim 1, characterized in that: The laser comprises an n-GaN substrate, an n-AlGaN confinement layer, an n-AlGaN or n-AlGaN / GaN superlattice electronic extension layer, a first InGaN waveguide layer, an InGaN / GaN quantum well light-emitting layer, a second InGaN waveguide layer, a p-AlGaN confinement layer, and a p-GaN ohmic contact layer arranged sequentially along a specified direction.

10. The method for growing a laser with an electronically extended structure as described in any one of claims 1-9, characterized in that, include: An n-type confinement layer, an n-type electron extension layer, a first waveguide layer, a light-emitting layer, a second waveguide layer, a p-type confinement layer, and a p-type ohmic contact layer are sequentially grown and stacked along a specified direction. Both the n-type electron extension layer and the n-type confinement layer are formed of Al-containing group III nitrides, and the Al content in the n-type electron extension layer is greater than that in the n-type confinement layer. This results in the potential barrier of the n-type electron extension layer being higher than the potential barriers of either the n-type confinement layer or the first waveguide layer, thereby reducing the movement speed of electrons moving from the n-type confinement layer to the light-emitting layer.

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