Vertical cavity surface emitting laser and method of manufacturing the same

Abstract

The application discloses a vertical cavity surface emitting laser and a manufacturing method thereof. The laser comprises a GaAs substrate, a first DBR layer formed on the GaAs substrate, an oxidation layer formed on the first DBR layer, a lattice gradient layer formed on the oxidation layer, a cladding layer formed on the lattice gradient layer, wherein the cladding layer comprises a first cladding layer and a second cladding layer stacked, a gain layer formed between the first cladding layer and the second cladding layer, and a second DBR layer formed on the cladding layer. The lattice gradient layer has different lattice constants in the thickness direction, and the lattice constant of the side of the lattice gradient layer close to the GaAs substrate matches the lattice constant of the GaAs substrate, and the lattice constant of the side of the lattice gradient layer close to the gain layer matches the lattice constant of the gain layer. The vertical cavity surface emitting laser and the manufacturing method thereof can flexibly expand the lasing wavelength to 1500 nm or above.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic technology, and in particular to a vertical cavity surface-emitting laser and its fabrication method. Background Technology

[0002] Vertical-cavity surface-emitting lasers (VCSELs) are semiconductor lasers with advantages such as low threshold current and easy integration, primarily used in fields like facial recognition, 3D sensing, and short-range optical communication. Currently, mature VCSELs are mainly based on GaAs materials, capable of generating lasers in the 800-1000nm range. InP-based materials can be used to generate lasers above 1300nm, primarily in edge-emitting laser structures for long-range optical communication. InP / InGaAsP long-wavelength DBRs with lattice matching to InP substrates have a low refractive index difference (<0.3), requiring more period numbers to achieve high reflectivity. Furthermore, the lack of mature and stable oxide hole technology for InP-based materials makes the fabrication of VCSELs above 1300nm complex, requiring multiple epitaxial layers, buried structures, and bonding processes. Therefore, long-wavelength VCSELs above 1300nm have not yet seen large-scale application.

[0003] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to provide a vertical cavity surface-emitting laser and its manufacturing method, which can flexibly extend the lasing wavelength to above 1500nm.

[0005] To achieve the above objectives, embodiments of the present invention provide a vertical-cavity surface-emitting laser, comprising: a GaAs substrate; a first DBR layer formed on the GaAs substrate; an oxide layer formed on the first DBR layer; a lattice-gradient layer formed on the oxide layer; a cladding layer formed on the lattice-gradient layer, the cladding layer comprising a first cladding layer and a second cladding layer stacked thereon; a gain layer formed between the first cladding layer and the second cladding layer; and a second DBR layer formed on the cladding layer; wherein the lattice-gradient layer has a different lattice constant in its thickness direction, and the lattice constant of the side of the lattice-gradient layer near the GaAs substrate matches the lattice constant of the GaAs substrate, and the lattice constant of the side of the lattice-gradient layer near the gain layer matches the lattice constant of the gain layer.

[0006] In one or more embodiments of the present invention, the GaAs substrate is a p-type doped GaAs substrate.

[0007] In one or more embodiments of the present invention, the material of the lattice gradient layer is selected from a compound semiconductor thin film material with tunable composition. By adjusting the composition of the compound semiconductor thin film material, the lattice constant of the lattice gradient layer in its thickness direction is changed.

[0008] In one or more embodiments of the present invention, the compound semiconductor thin film material is selected from In x Ga 1-x As, GaAs x Sb 1-x Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y As, Ga x Al 1-x As y Sb 1-y Ga x In 1-x As y Sb 1-y .

[0009] In one or more embodiments of the present invention, the thickness D1 of the lattice gradient layer satisfies: D1*N1=m*λ / 4, where N1 is the average optical refractive index of the lattice gradient layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical cavity surface-emitting laser.

[0010] In one or more embodiments of the present invention, the lattice gradient layer is a p-type doped lattice gradient layer.

[0011] In one or more embodiments of the present invention, the first DBR layer is a p-type doped Bragg mirror layer, and the material of the first DBR layer is selected from compound semiconductor materials, wherein the compound semiconductor material is selected from GaAs or Al. x Ga 1- x As, where the Al x Ga 1-x The lattice constant of As matches the lattice constant of the GaAs substrate.

[0012] In one or more embodiments of the present invention, the second DBR layer is a dielectric Bragg reflector layer composed of a dielectric thin film, and the material of the second DBR layer is selected from SiO2, Si3N4 or Si.

[0013] In one or more embodiments of the present invention, the Bragg reflector layer is a multilayer structure, and the layer thickness D2 of each layer satisfies: D2*N2=λ / 4, where N2 is the optical refractive index of each layer and λ is the wavelength of the vertical cavity surface-emitting laser.

[0014] In one or more embodiments of the present invention, the oxide layer comprises at least one AlGaAs layer or one AlAs layer, wherein the Al content of the AlGaAs layer is higher than 95%.

[0015] In one or more embodiments of the present invention, the oxide layer further includes an Al layer with an Al content of less than 90%. x Ga 1-x As layer or GaAs layer.

[0016] In one or more embodiments of the present invention, the total thickness D3 of the oxide layer satisfies: D3*N3=λ / 4, where N3 is the average optical refractive index of the oxide layer and λ is the wavelength of the vertical cavity surface-emitting laser.

[0017] In one or more embodiments of the present invention, oxide pores are formed in the oxide layer.

[0018] In one or more embodiments of the present invention, the materials of the first coating layer and the second coating layer are selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As.

[0019] Wherein, Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As matches the lattice constant of InP; or, the Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As is less than 1% mismatched with the lattice constant of InP.

[0020] In one or more embodiments of the present invention, the gain layer comprises a plurality of stacked quantum well layers, with an isolation layer formed between adjacent quantum well layers, the isolation layer being selected from InP or Ga.x In 1-x As y P 1-y or Ga x Al y In 1-x-y As.

[0021] In one or more embodiments of the present invention, each group of quantum well layers includes a plurality of stacked quantum well units, each quantum well unit including a wetting layer, a plurality of quantum dot units or a plurality of quantum short wires arranged on the wetting layer, and a capping layer covering the plurality of quantum dot units or the plurality of quantum short wires.

[0022] In one or more embodiments of the present invention, the material of the quantum dot unit or the quantum short wire is selected from InAs, GaSb, InSb, and InAs. x Sb 1-x or Ga x In 1-x As y Sb 1-y The material of the wetting layer is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As, the material of the capping layer is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As.

[0023] Wherein, Ga x In 1-x As y P 1-y or Ga x Al y In 1-x-y The lattice constant of As matches the lattice constant of InP; or, the Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As is less than 1% mismatched with the lattice constant of InP.

[0024] In one or more embodiments of the present invention, the total thickness D4 of the gain layer satisfies: D4*N4=m*λ / 4, where N4 is the average optical refractive index of the gain layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical cavity surface-emitting laser.

[0025] In one or more embodiments of the present invention, the vertical-cavity surface-emitting laser further includes a contact layer formed on the cladding layer, wherein the material of the contact layer is selected from InP or Ga. x In 1-x As, the doping concentration of the contact layer is 5E18~1E19cm⁻¹ -3 .

[0026] In one or more embodiments of the present invention, a first electrode is formed on the contact layer, the first electrode comprising a single layer or multiple layers of metal, and the material of the first electrode is selected from AuGe, AuGe / Ni or AuGe / Ni / Au.

[0027] In one or more embodiments of the present invention, a second electrode is formed on the GaAs substrate, the second electrode comprising a single layer or multiple layers of metal, and the material of the second electrode is selected from Au / Zn / Au or Ti / Pt / Au.

[0028] An embodiment of the present invention also provides a method for fabricating a vertical-cavity surface-emitting laser (VCSEL), comprising: providing a GaAs substrate; sequentially growing a first DBR layer and an oxide layer on the GaAs substrate; growing a lattice-gradient layer on the oxide layer, wherein the material of the lattice-gradient layer is selected from a compositionally tunable compound semiconductor thin film material, and by adjusting the composition of the compound semiconductor thin film material during the growth of the lattice-gradient layer, the lattice constant of the lattice-gradient layer in its thickness direction is changed, so that the lattice constant of the lattice-gradient layer on the side closer to the GaAs substrate matches the lattice constant of the GaAs substrate, and the lattice constant on the side farther from the GaAs substrate matches the lattice constant of the gain layer to be grown; sequentially growing a first cladding layer, a gain layer, and a second cladding layer on the lattice-gradient layer; and depositing a second DBR layer on the second cladding layer. In one or more embodiments of the present invention, before growing the second DBR layer, a contact layer is further grown on the second cladding layer, and the second DBR layer is deposited on the contact layer.

[0029] In one or more embodiments of the present invention, the method further includes the steps of forming a first electrode on the contact layer and forming a second electrode on the GaAs substrate.

[0030] In one or more embodiments of the present invention, before forming the first electrode and the second electrode, the method further includes etching the second DBR layer to form a platform structure and oxidizing the oxide layer to form an oxide hole.

[0031] Compared with the prior art, the vertical cavity surface emission laser and its fabrication method of the present invention can flexibly extend the lasing wavelength to above 1500nm by utilizing a lattice gradient layer and a gain layer that is insensitive to defects.

[0032] The vertical cavity surface-emitting laser and its fabrication method according to the embodiments of the present invention utilize mature high-reflectivity DBR and high-Al layer oxide hole photoelectric confinement technology (based on GaAs substrate) to grow a gain layer capable of lasing long wavelengths through a lattice gradient method. The gain layer is composed of low-dimensional structures such as quantum dots or quantum dashes that are insensitive to epitaxial defects, thereby obtaining a long-wavelength VCSEL device with simple epitaxial and device fabrication processes and low cost.

[0033] The vertical cavity surface-emitting laser and its fabrication method according to embodiments of the present invention have a gain layer composed of low-dimensional structures such as quantum dots or quantum short wires, which have the characteristics of low spontaneous emission noise and low threshold current, and are expected to realize single-photon emission. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of a vertical cavity surface-emitting laser according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the gain layer of a vertical cavity surface-emitting laser according to an embodiment of the present invention;

[0036] Figure 3 It is the optical absorption spectrum valley near 1640nm formed by the epitaxial resonant cavity of the vertical cavity surface-emitting laser according to an embodiment of the present invention;

[0037] Figure 4 The refractive index distribution and optical standing wave electric field distribution at 1640nm wavelength are corresponding to the epitaxial resonant cavity of a vertical cavity surface-emitting laser according to an embodiment of the present invention.

[0038] Figure 5 This is a flowchart of a method for manufacturing a vertical cavity surface-emitting laser according to an embodiment of the present invention;

[0039] Figures 6a-6e This is a schematic diagram illustrating the steps of a method for fabricating a vertical cavity surface-emitting laser according to an embodiment of the present invention. Detailed Implementation

[0040] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0041] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0042] As mentioned in the background section, existing mature VCSELs are mainly based on two material systems: GaAs and InP. GaAs can generate lasers in the 800-1000 nm range, while InP can generate lasers above 1300 nm, primarily used in edge-emitting laser structures for long-distance optical communication. However, the refractive index difference of InP / InGaAsP long-wavelength DBRs, which are lattice-matched to InP substrates, is relatively low (<0.3), requiring more periods to achieve high reflectivity. Furthermore, the lack of mature and stable oxide hole technology for InP-based materials complicates the fabrication of VCSELs above 1300 nm, necessitating multiple epitaxial layers, buried structures, and bonding processes. Therefore, long-wavelength VCSELs above 1300 nm have not been widely adopted.

[0043] This invention proposes a vertical cavity surface-emitting laser that combines GaAs and InP-based material systems. It utilizes the mature high-reflectivity DBR and high-Al oxide hole photoelectric confinement technology in the GaAs material system to grow a long-wavelength gain layer in the InP-based material system through a lattice gradient method, thereby obtaining a long-wavelength VCSEL device with simple epitaxial and device fabrication processes and low cost.

[0044] like Figure 1 As shown, a vertical-cavity surface-emitting laser according to an embodiment of the present invention includes a GaAs substrate 10; a first DBR layer 20 formed on the GaAs substrate 10; an oxide layer 30 formed on the first DBR layer; a lattice-gradient layer 40 formed on the oxide layer 30; a cladding layer formed on the lattice-gradient layer 40, the cladding layer including a first cladding layer 51 and a second cladding layer 52 stacked thereon; a gain layer 60 formed between the first cladding layer 51 and the second cladding layer 52; a contact layer 70 formed on the cladding layer; and a second DBR layer 80 formed on the cladding layer and the contact layer 70. The lattice-gradient layer 40 has a different lattice constant in its thickness direction, and the lattice constant of the lattice-gradient layer 40 near the GaAs substrate 10 matches the lattice constant of the GaAs substrate 10, and the lattice constant of the lattice-gradient layer 40 near the gain layer 60 matches the lattice constant of the gain layer 60.

[0045] The GaAs substrate 10 is preferably a p-type doped GaAs(001) substrate with a bias angle. For example, a p-type GaAs(001) substrate with a bias angle of 6° can be used.

[0046] The first DBR layer 20 and the second DBR layer 80 are layered structures consisting of two optical media materials with different refractive indices that alternate periodically, and have high reflectivity for light within the working wavelength range.

[0047] In this embodiment, the first DBR layer 20 is a p-type doped Bragg mirror layer, and the material of the first DBR layer 20 is selected from compound semiconductor materials, specifically GaAs or Al. x Ga 1-x As, where Al x Ga 1-x The lattice constant of As matches the lattice constant of the GaAs substrate 10. The Bragg mirror layer is a multilayer structure, and the layer thickness D2 of each layer satisfies: D2*N2=λ / 4, where N2 is the optical refractive index of each layer and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the first DBR layer 20 can be a 25-period p-type doped layer with a concentration of 1E19cm⁻¹. -3 121nm-Al 0.12 Ga 0.88 As / 136nm-Al 0.90 Ga 0.10 As. The second DBR layer 80 is a dielectric Bragg reflector layer composed of a dielectric thin film, and the material of the second DBR layer 80 is selected from SiO2, Si3N4, or Si. The Bragg reflector layer is also a multilayer structure, and the layer thickness D2 of each layer satisfies: D2*N2=λ / 4, where N2 is the optical refractive index of each layer, and λ is the wavelength of the vertical cavity surface-emitting laser. For example, the second DBR layer 80 can be a 15-cycle undoped 275nm-SiO2 / 210nm-Si3N4, but it is not limited to this. In other embodiments of the present invention, the first DBR layer 20 and the second DBR layer 80 can also be made of other semiconductor optical materials, which are also within the protection scope of the present invention.

[0048] In this embodiment, the oxide layer 30 can be a p-type doped oxide layer. The oxide layer 30 includes at least one AlGaAs layer or one pure AlAs layer, wherein the Al content of the AlGaAs layer is higher than 95%. The oxide layer 30 also includes an Al layer with an Al content lower than 90%. x Ga 1-xAn As or GaAs layer. The total thickness D3 of the oxide layer 30 satisfies: D3*N3=λ / 4, where N3 is the average optical refractive index of the oxide layer and λ is the wavelength of the vertical-cavity surface-emitting laser. Partially unoxidized regions in the oxide layer 30 form oxide holes 31. After the high-Al layer is partially oxidized to form an oxide, it forms a radial optical waveguide structure with the unoxidized portion, achieving current injection confinement. For example, the oxide layer 30 can be p-type doped 3E18cm⁻¹. -3 50nm Al 0.98 Ga 0.02 As and p-type doping 5E18cm -3 80nm Al 0.30 Ga 0.70 As.

[0049] The lattice gradient layer 40 is composed of a compound semiconductor thin film material with tunable composition. By adjusting the composition of the compound semiconductor thin film material, the lattice constant of the lattice gradient layer 40 in its thickness direction is changed, so that the lattice constant of the lattice gradient layer 40 near the GaAs substrate 10 matches the lattice constant of the GaAs substrate 10, and the lattice constant of the lattice gradient layer 40 near the gain layer 60 matches the lattice constant of the gain layer 60. It can be understood that by adjusting the composition of the compound semiconductor thin film material, the lattice constant of the lattice gradient layer 40 can be made to change linearly from the GaAs substrate 10 to the gain layer 60.

[0050] In this embodiment, the lattice gradient layer 40 is also a p-type doped lattice gradient layer. The compound semiconductor thin film material in the lattice gradient layer 40 is selected from the ternary material In. x Ga 1-x As, GaAs x Sb 1-x Or quaternary material Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y As, Ga x Al 1-x As y Sb 1-y Ga x In 1-x As y Sb 1-y The thickness D1 of the lattice-graded layer 40 satisfies: D1*N1=m*λ / 4, where N1 is the average optical refractive index of the lattice-graded layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the lattice-graded layer 40 can be a p-type doped 3E18cm² laser with an In composition graded from 0 to 53%.-3 A 148nm InGaAs lattice gradient layer.

[0051] refer to Figure 2 As shown, the gain layer 60 can be composed of multiple sets of multilayer quantum dot units or quantum short wires. In this embodiment, the gain layer 60 includes multiple sets of stacked quantum well layers 61, with an isolation layer 62 formed between adjacent quantum well layers 61. The material of the isolation layer 62 is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As. Each quantum well layer 61 includes multiple stacked quantum well units. Each quantum well unit includes a wetting layer 611, multiple quantum dot units or multiple quantum short wires 612 arranged on the wetting layer 611, and a capping layer 613 covering the multiple quantum dot units or multiple quantum short wires 612. The material of the quantum dot units or quantum short wires 612 is selected from InAs, GaSb, InSb, and InAs. x Sb 1-x or Ga x In 1-x As y Sb 1-y The material of the impregnation layer 611 is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As. The material of the capping layer 613 is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y It should be noted that, preferably, the lattice constant of the lattice gradient layer 40 on the side closest to the gain layer 60 matches the lattice constant of the isolation layer 62.

[0052] The total thickness D4 of the gain layer 60 satisfies: D4*N4=m*λ / 4, where N4 is the average optical refractive index of the gain layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the gain layer comprises three sets of InAs multi-quantum dot layers, each set containing six periods of 1nm-InAs / 15nm-Ga... 0.23 In 0.77 As 0.5 P 0.5A 130nm-InP isolation layer is grown between each group of quantum dots.

[0053] In this embodiment, the lattice constants of the first cladding layer 51 and the second cladding layer 52 are matched with those of the gain layer 60, and preferably with those of the isolation layer 62 in the gain layer 60. In a preferred embodiment, if the material of the gain layer 60 is selected from InP, the materials of the first cladding layer 51 and the second cladding layer 52 can be selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As, and Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As matches that of InP. In other specific embodiments, Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As can also have a mismatch of less than 1% with the lattice constant of InP. For example, the first coating layer 51 and the second coating layer 52 can both be 65nm-InP.

[0054] In this embodiment, the contact layer 70 can be an n-type doped contact layer. The material of the contact layer 70 is selected from InP or Ga, a ternary material that matches the InP lattice. x In 1-x As, the doping concentration of contact layer 70 is 5E18~1E19cm. -3 For example, the contact layer 70 can be n-type doped 5E18cm. -3 118nm-In contact layer 0.53 Ga 0.47 As.

[0055] refer to Figure 3 and Figure 4 As shown, each epitaxial layer on the GaAs substrate 10 constitutes an optical resonant cavity. The resonant cavity generates a valley of optical reflectivity near the laser wavelength of the optical reflection spectrum. The light wave that forms the laser forms an optical standing wave in the resonant cavity. The gain layer 60 needs to be located at the antinode position with the highest standing wave intensity. When the gain layer 60 is multilayer, the intensity of multiple maximum antinodes needs to be consistent. The high Al layer in the oxide layer 30 needs to be located at the node position adjacent to the lattice gradient layer 40.

[0056] A first electrode 91 is formed on the contact layer 70. The first electrode 91 comprises a single layer or multiple layers of metal, and the metal forms an ohmic contact with the contact layer 70. The first electrode 91 is an n-type electrode, and the material is selected from AuGe, AuGe / Ni, or AuGe / Ni / Au.

[0057] A second electrode 92 is formed on the GaAs substrate 10. The second electrode 92 includes a single layer or multiple layers of metal. The second electrode is a p-type electrode, and the material is selected from Au / Zn / Au or Ti / Pt / Au.

[0058] refer to Figure 5 As shown, the present invention also provides a method for fabricating a vertical-cavity surface-emitting laser, comprising:

[0059] S1 provides a GaAs substrate 10;

[0060] S2, the first DBR layer 20 and the oxide layer 30 are sequentially grown on the GaAs substrate 10;

[0061] S3, a lattice gradient layer 40 is grown on the oxide layer 30. The material of the lattice gradient layer 40 is selected from a compound semiconductor thin film material with adjustable composition. By adjusting the composition of the compound semiconductor thin film material during the growth of the lattice gradient layer 40, the lattice constant of the lattice gradient layer 40 in its own thickness direction is changed, so that the lattice constant of the side of the lattice gradient layer 40 close to the GaAs substrate 10 matches the lattice constant of the GaAs substrate 40, and the lattice constant of the side away from the GaAs substrate 40 matches the lattice constant of the gain layer 60 to be grown.

[0062] S4, a first cladding layer 51, a gain layer 60 and a second cladding layer 52 are sequentially grown on the lattice gradient layer 40.

[0063] S5, a contact layer 70 is grown on the second covering layer 52;

[0064] S6, deposit the second DBR layer 80 on the contact layer 70;

[0065] S7, a first electrode 91 is formed on the contact layer 70 and a second electrode 92 is formed on the GaAs substrate 10.

[0066] Figures 6a-6e This is a schematic diagram illustrating the steps of a method for fabricating a vertical-cavity surface-emitting laser (VCSEL) according to one embodiment of the present invention. The method for fabricating a VCSEL according to the present invention will be described in detail below with reference to the schematic diagram.

[0067] like Figure 6aAs shown, a GaAs substrate 10 is provided, on which a first DBR layer 20 and an oxide layer 30 are sequentially grown.

[0068] Preferably, the GaAs substrate 10 is a p-type doped GaAs(001) substrate with a bias angle. For example, a p-type GaAs(001) substrate with a bias angle of 6° can be used.

[0069] The first DBR layer 20 is a layered structure consisting of two optical media materials with different refractive indices that alternate periodically, exhibiting high reflectivity for light within the operating wavelength range. The first DBR layer 20 is a p-type doped Bragg mirror layer, and the material of the first DBR layer 20 is selected from compound semiconductor materials, specifically GaAs or Al. x Ga 1-x As, where Al x Ga 1-x The lattice constant of As matches the lattice constant of the GaAs substrate 10. The Bragg mirror layer is a multilayer structure, and the layer thickness D2 of each layer satisfies: D2*N2=λ / 4, where N2 is the optical refractive index of each layer and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the first DBR layer 20 can be a 25-period p-type doped layer with a concentration of 1E19cm⁻¹. -3 121nm-Al 0.12 Ga 0.88 As / 136nm-Al 0.90 Ga 0.10 As.

[0070] The oxide layer 30 can be a p-type doped oxide layer. The oxide layer 30 includes at least one AlGaAs layer or one pure AlAs layer, wherein the Al content of the AlGaAs layer is higher than 95%. The oxide layer 30 may also include an Al layer with an Al content lower than 90%. x Ga 1-x An As or GaAs layer. The total thickness D3 of the oxide layer 30 satisfies: D3*N3=λ / 4, where N3 is the average optical refractive index of the oxide layer and λ is the wavelength of the vertical-cavity surface-emitting laser. Partially unoxidized regions in the oxide layer 30 form oxide holes 31. After the high-Al layer is partially oxidized to form an oxide, it forms a radial optical waveguide structure with the unoxidized portion, achieving current injection confinement. For example, the oxide layer 30 can be p-type doped 3E18cm⁻¹. -3 50nm Al 0.98 Ga 0.02 As and p-type doping 5E18cm -3 80nm Al 0.30 Ga 0.70 As.

[0071] like Figure 6b As shown, a lattice gradient layer 40 is grown on the oxide layer 30. The material of the lattice gradient layer 40 is selected from a compound semiconductor thin film material with tunable composition. By adjusting the composition of the compound semiconductor thin film material during the growth of the lattice gradient layer 40, the lattice constant of the lattice gradient layer 40 in its thickness direction is changed, so that the lattice constant of the side of the lattice gradient layer 40 close to the GaAs substrate 10 matches the lattice constant of the GaAs substrate 40, and the lattice constant of the side away from the GaAs substrate 40 matches the lattice constant of the gain layer 60 to be grown.

[0072] It is understandable that by adjusting the composition of the compound semiconductor thin film material, the lattice constant of the lattice gradient layer 40 can be linearly varied from the GaAs substrate 10 to the gain layer 60. The lattice gradient layer 40 is also a p-type doped lattice gradient layer. The compound semiconductor thin film material in the lattice gradient layer 40 is selected from the ternary material In... x Ga 1-x As, GaAs x Sb 1-x Or quaternary material Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y As, Ga x Al 1-x As y Sb 1-y Ga x In 1-x As y Sb 1-y The thickness D1 of the lattice-graded layer 40 satisfies: D1*N1=m*λ / 4, where N1 is the average optical refractive index of the lattice-graded layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the lattice-graded layer 40 can be a p-type doped 3E18cm² laser with an In composition graded from 0 to 53%. -3 A 148nm InGaAs lattice gradient layer.

[0073] like Figure 6c As shown, a first cladding layer 51, a gain layer 60, and a second cladding layer 52 are sequentially grown on the lattice gradient layer 40; a contact layer 70 is grown on the second cladding layer 52; and a second DBR layer 80 is deposited on the contact layer 70.

[0074] The lattice constants of the first cladding layer 51 and the second cladding layer 52 are matched with those of the gain layer 60. When the material of the gain layer 60 is selected from InP, the materials of the first cladding layer 51 and the second cladding layer 52 can be selected from InP or Ga. xIn 1-x As y P 1-y or Ga x Al y In 1-x-y As, and Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As matches that of InP. In other specific embodiments, Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y The lattice constant of As can also be less than 1% mismatched with the lattice constant of InP. For example, the first coating layer 51 and the second coating layer 52 can both be 65nm-InP.

[0075] The gain layer 60 can be composed of multiple sets of multilayer quantum dot units or quantum short wires. In this embodiment, the gain layer 60 includes multiple sets of stacked quantum well layers 61, with an isolation layer 62 formed between adjacent quantum well layers 61. The material of the isolation layer 62 is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As. Each quantum well layer comprises multiple stacked quantum well units. Each quantum well unit includes a wetting layer 611, multiple quantum dot units or multiple quantum short wires 612 arranged on the wetting layer 611, and a capping layer 613 covering the multiple quantum dot units or multiple quantum short wires 612. The material of the quantum dot units or quantum short wires 612 is selected from InAs, GaSb, InSb, and InAs. x Sb 1-x or Ga x In 1-x As y Sb 1-y The material of the impregnation layer 611 is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As. The material of the capping layer 613 is selected from InP or Ga. x In1-x As y P 1-y or Ga x Al y In 1-x- y As should be noted, the thickness of the isolation layer 62 is the largest among all the layers of the gain layer 60. Preferably, the lattice constant of the lattice-gradient layer 40 closest to the gain layer 60 matches the lattice constant of the isolation layer 62. The total thickness D4 of the gain layer 60 satisfies: D4*N4=m*λ / 4, where N4 is the average optical refractive index of the gain layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the gain layer comprises three groups of InAs multi-quantum dot layers, each group containing six periods of 1nm-InAs / 15nm-Ga. 0.23 In 0.77 As 0.5 P 0.5 A 130nm-InP isolation layer is grown between each group of quantum dots.

[0076] The contact layer 70 can be an n-type doped contact layer. The material of the contact layer 70 is selected from InP or a ternary material Ga that matches the InP lattice. x In 1-x As, the doping concentration of contact layer 70 is 5E18~1E19cm. -3 For example, the contact layer 70 can be n-type doped 5E18cm. -3 118nm-In contact layer 0.53 Ga 0.47 As.

[0077] The second DBR layer 80 is a layered structure consisting of two optical media materials with alternating periods of two different refractive indices, exhibiting high reflectivity for light within the operating wavelength range. The second DBR layer 80 is a dielectric Bragg reflector layer composed of a dielectric thin film, and the material of the second DBR layer 80 is selected from SiO2, Si3N4, or Si. The Bragg reflector layer is also a multilayer structure, with the layer thickness D2 satisfying: D2*N2=λ / 4, where N2 is the optical refractive index of each layer, and λ is the wavelength of the vertical-cavity surface-emitting laser. For example, the second DBR layer 80 can be a 15-period undoped 275nm-SiO2 / 210nm-Si3N4 layer.

[0078] like Figure 6d As shown, the second DBR layer 80 is etched to form a platform structure, and the oxide layer 30 is oxidized to form oxide holes 31.

[0079] like Figure 6eAs shown, a first electrode 91 is formed on the contact layer 70 on the outer side of the platform structure and a second electrode 92 is formed on the GaAs substrate 10.

[0080] The first electrode 91 comprises one or more layers of metal, forming an ohmic contact with the contact layer 70. The first electrode 91 is an n-type electrode, and the material is selected from AuGe, AuGe / Ni, or AuGe / Ni / Au. The second electrode 92 comprises one or more layers of metal, and is a p-type electrode, with the material selected from Au / Zn / Au or Ti / Pt / Au.

[0081] The vertical cavity surface-emitting laser of the present invention and its fabrication method are described below through a specific embodiment.

[0082] A 25-cycle p-type doped GaAs(001) substrate with a 6° offset (110) was grown using MOCVD with a doping concentration of 1E19cm⁻¹. -3 121nm-Al 0.12 Ga 0.88 As / 136nm-Al 0.90 Ga 0.10 As the first DBR layer, a p-type doped 3E18cm layer is grown on the first DBR layer. -3 50nm Al 0.98 Ga 0.02 As and p-type doping 5E18cm -3 80nm Al 0.30 Ga 0.70 As is used as the oxide layer, p-type doped 3E18cm⁻¹ with In composition gradually varying from 0% to 53% is grown on the oxide layer. -3 A 148nm InGaAs lattice-gradient layer is constructed, on which a first cladding layer of 65nm InP, a gain layer, and a second cladding layer of 65nm InP are grown. The gain layer comprises three groups of InAs multi-quantum dot layers, each group containing six periods of 1nm InAs / 15nm GaAs. 0.23 In 0.77 As 0.5 P 0.5 A 130 nm InP isolation layer is grown between each group of quantum dots, and an n-type doped 5E18 cm⁻¹ layer is grown on top of the second cladding layer. -3 118nm-In contact layer 0.53 Ga 0.47 As, a 15-cycle undoped 275nm-SiO2 / 210nm-Si3N4 second DBR layer is deposited on the n-type contact layer.

[0083] The second DBR layer is etched, and a micro-mesa with a diameter of 30 μm is fabricated using the device fabrication process. After the mesa is fabricated, a 6 μm oxide hole is formed in the oxide layer through an oxidation process. The n-electrode and p-electrode are fabricated on the n-type contact layer and the GaAs substrate using Au / Zn / Au and AuGe / Ni / Au multilayer metals, respectively.

[0084] Compared with the prior art, the vertical cavity surface emission laser and its fabrication method of the present invention can flexibly extend the lasing wavelength to above 1500nm by utilizing a lattice gradient layer and a gain layer that is insensitive to defects.

[0085] The vertical cavity surface-emitting laser and its fabrication method according to the embodiments of the present invention utilize mature high-reflectivity DBR and high-Al layer oxide hole photoelectric confinement technology (based on GaAs substrate) to grow a gain layer capable of lasing long wavelengths through a lattice gradient method. The gain layer is composed of low-dimensional structures such as quantum dots or quantum dashes that are insensitive to epitaxial defects, thereby obtaining a long-wavelength VCSEL device with simple epitaxial and device fabrication processes and low cost.

[0086] The vertical cavity surface-emitting laser and its fabrication method according to embodiments of the present invention have a gain layer composed of low-dimensional structures such as quantum dots or quantum short wires, which have the characteristics of low spontaneous emission noise and low threshold current, and are expected to realize single-photon emission.

[0087] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A vertical-cavity surface-emitting laser, characterized in that, include: GaAs substrate; The first DBR layer is formed on the GaAs substrate, and the first DBR layer is a p-type doped Bragg mirror layer; An oxide layer is formed on the first DBR layer; A lattice-gradient layer is formed on the oxide layer; A coating layer is formed on the lattice gradient layer, the coating layer comprising a first coating layer and a second coating layer stacked together; A gain layer is formed between the first cladding layer and the second cladding layer. The gain layer includes multiple sets of quantum well layers stacked together. An isolation layer is formed between adjacent quantum well layers. Each set of quantum well layers includes multiple stacked quantum well units. Each quantum well unit includes a wetting layer, multiple quantum dot units or multiple quantum short wires arranged on the wetting layer, and a capping layer covering the multiple quantum dot units or multiple quantum short wires. as well as The second DBR layer is formed on the coating layer, and the second DBR layer is a dielectric Bragg reflector layer composed of a dielectric thin film; The lattice gradient layer has different lattice constants in its thickness direction, and the lattice constant of the side of the lattice gradient layer near the GaAs substrate matches the lattice constant of the GaAs substrate, and the lattice constant of the side of the lattice gradient layer near the gain layer matches the lattice constant of the gain layer.

2. The vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The lattice gradient layer is made of a compositionally tunable compound semiconductor thin film material. By adjusting the composition of the compound semiconductor thin film material, the lattice constant of the lattice gradient layer in its thickness direction is changed. The compound semiconductor thin film material is selected from In... x Ga 1-x As, GaAs x Sb 1-x Ga x In 1-x As y P 1-y Ga x Al y In 1-x-y As, Ga x Al 1-x As y Sb 1-y Ga x In 1-x As y Sb 1-y ; and / or, The thickness D1 of the lattice gradient layer satisfies: D1*N1=m*λ / 4, where N1 is the average optical refractive index of the lattice gradient layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical cavity surface-emitting laser.

3. The vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The material of the first DBR layer is selected from compound semiconductor materials, and the compound semiconductor material is selected from GaAs or Al. x Ga 1-x As, where the Al x Ga 1-x The lattice constant of As matches the lattice constant of the GaAs substrate; and / or, The material of the second DBR layer is selected from SiO2, Si3N4 or Si.

4. The vertical-cavity surface-emitting laser as described in claim 3, characterized in that, The Bragg reflector layer has a multi-layer structure, and the layer thickness D2 of each layer satisfies: D2*N2=λ / 4, where N2 is the optical refractive index of each layer and λ is the wavelength of the vertical cavity surface-emitting laser.

5. The vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The oxide layer comprises at least one AlGaAs layer or one AlAs layer, wherein the Al content of the AlGaAs layer is higher than 95%; and / or, The total thickness D3 of the oxide layer satisfies: D3*N3=λ / 4, where N3 is the average optical refractive index of the oxide layer, λ is the wavelength of the vertical-cavity surface-emitting laser; and / or The materials of the first coating layer and the second coating layer are selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As.

6. The vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The material of the isolation layer is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As.

7. The vertical-cavity surface-emitting laser as described in claim 6, characterized in that, The quantum dot unit or the quantum short wire is made of InAs, GaSb, InSb, or InAs. x Sb 1-x or Ga x In 1-x As y Sb 1-y The material of the wetting layer is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As, the material of the capping layer is selected from InP or Ga. x In 1-x As y P 1-y or Ga x Al y In 1-x-y As; and / or The total thickness D4 of the gain layer satisfies: D4*N4=m*λ / 4, where N4 is the average optical refractive index of the gain layer, m is a natural number greater than or equal to 1, and λ is the wavelength of the vertical cavity surface-emitting laser.

8. The vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The vertical-cavity surface-emitting laser further includes a contact layer formed on the cladding layer, the material of which is selected from InP or Ga. x In 1-x As, the doping concentration of the contact layer is 5E18~1E19 cm⁻¹ -3 .

9. The vertical-cavity surface-emitting laser as described in claim 8, characterized in that, A first electrode is formed on the contact layer. The first electrode comprises a single layer or multiple layers of metal, and the material of the first electrode is selected from AuGe, AuGe / Ni, or AuGe / Ni / Au; and / or A second electrode is formed on the GaAs substrate. The second electrode comprises a single layer or multiple layers of metal, and the material of the second electrode is selected from Au / Zn / Au or Ti / Pt / Au.

10. A method for fabricating a vertical-cavity surface-emitting laser, characterized in that, include: Provide GaAs substrates; A first DBR layer and an oxide layer are sequentially grown on the GaAs substrate, wherein the first DBR layer is a p-type doped Bragg mirror layer. A lattice gradient layer is grown on the oxide layer. The material of the lattice gradient layer is selected from a compound semiconductor thin film material with tunable composition. By adjusting the composition of the compound semiconductor thin film material during the growth of the lattice gradient layer, the lattice constant of the lattice gradient layer in its thickness direction is changed, so that the lattice constant of the lattice gradient layer on the side closer to the GaAs substrate matches the lattice constant of the GaAs substrate, and the lattice constant on the side farther from the GaAs substrate matches the lattice constant of the gain layer to be grown. A first cladding layer, a gain layer, and a second cladding layer are sequentially grown on the lattice gradient layer. The gain layer includes multiple sets of quantum well layers stacked together. An isolation layer is formed between adjacent quantum well layers. Each set of quantum well layers includes multiple stacked quantum well units. Each quantum well unit includes a wetting layer, multiple quantum dot units or multiple quantum short wires arranged on the wetting layer, and a capping layer covering the multiple quantum dot units or multiple quantum short wires. A second DBR layer is deposited on the second coating layer. The second DBR layer is a dielectric Bragg reflector layer composed of a dielectric thin film.

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