Non-oxidation limited vertical cavity surface emitting laser and preparation method thereof

Abstract

The application relates to the technical field of lasers, in particular to a non-oxidation-limiting vertical cavity surface emitting laser and a preparation method thereof, which comprises, from bottom to top, a substrate, a buffer layer, an N-type DBR, an N-type cladding layer, an active region, a P-type cladding layer, a limiting layer, a P-type DBR, a contact layer and a passivation layer, wherein the material of the limiting layer is Fe-doped AlGaAs. When the layer is epitaxially grown by MOCVD, iron (Fe) is introduced as a deep level dopant, the deep acceptor level (about 0.47 eV from the top of the valence band) formed by Fe in AlGaAs compensates the background carriers, the material presents a semi-insulating characteristic (the resistivity can reach 10 7 -10 11 Ω·cm), thereby effectively blocking the expansion of the transverse current. The thermal conductivity (10-25 watts per meter kelvin) of the Fe-doped AlGaAs is 15-35 times that of aluminum oxide (0.7 watts per meter kelvin), which significantly improves the heat dissipation performance of the device.

Description

Technical Field

[0001] This application relates to the technical field of lasers, and in particular to a non-oxidation-confined vertical-cavity surface-emitting laser and its fabrication method. Background Technology

[0002] A vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser that emits laser light along a direction perpendicular to the semiconductor substrate. Compared with traditional edge-emitting lasers, VCSELs have advantages such as low threshold current, circular beam cross-section, ease of two-dimensional integration, and on-chip testing, making them the core light source device in short-distance optical interconnect systems.

[0003] Currently, commercially available 850nm VCSELs primarily employ selective wet oxidation technology to form the current- and optically confined structures. Although oxidation-confined VCSELs have achieved large-scale commercial application, this approach suffers from the following fundamental technical drawbacks: High thermal resistance limits heat dissipation performance: Al2O3 has a thermal conductivity of only about 1.5 W / m·K, which is much lower than that of semiconductor materials. The oxide layer becomes a bottleneck in the heat conduction path, making it difficult to effectively dissipate heat from the active region, thus limiting the device's performance in high-power and high-temperature environments. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a non-oxidation-confined vertical-cavity surface-emitting laser and its fabrication method.

[0005] One objective of this application is to provide a non-oxidation-confined vertical-cavity surface-emitting laser, employing the following technical solution: A non-oxidation-confined vertical-cavity surface-emitting laser includes, from bottom to top, a substrate, a buffer layer, an N-type DBR, an N-type cladding, an active region, a P-type cladding, a confinement layer, a P-type DBR, a contact layer, and a passivation layer, wherein the confinement layer is made of Fe-doped AlGaAs.

[0006] By employing the above technical solution, iron (Fe) is introduced as a deep-level dopant during MOCVD epitaxial growth. The deep principal level (approximately 0.47 eV from the valence band top) formed by Fe in AlGaAs compensates for background carriers, enabling the material to exhibit semi-insulating properties (resistivity up to 10⁻⁶ eV). 7 -10 11 (Ω·cm), thus effectively blocking the spread of transverse current.

[0007] Iron (Fe) is a transition metal impurity in group III-V semiconductors. In GaAs, Fe atoms occupy Ga sites and, as a dominant impurity, introduce two main acceptor levels in the band gap: the dominant acceptor level is located approximately 0.51 electron volts above the valence band top (corresponding to Fe). 2+ / Fe3+ (charge state transition), the secondary acceptor level is located approximately 0.88 electron volts above the top of the valence band (corresponding to Fe). + / Fe 2+ (charge state transition).

[0008] In N-type GaAs or AlGaAs, Fe is deeply trapped by electrons from the valence band in the principal energy level, undergoing the following compensation reaction: Fe 3+ +e - →Fe 2+ When the Fe doping concentration (approximately 1017 ohm-cmm) is slightly higher than the background donor concentration, almost all shallow donors are compensated, the Fermi level is pinned near the deep Fe level, and the material exhibits a high resistivity of 106–108 ohm-cmm, effectively blocking transverse current. Simultaneously, the thermal conductivity of Fe-doped AlGaAs (10-25 W / m Kelvin) is 15–35 times that of alumina (0.7 W / m Kelvin), significantly improving the device's heat dissipation performance.

[0009] Preferably, an aperture is formed at the center of the confinement layer by etching.

[0010] By adopting the above technical solution, the size and shape of the current injection window are precisely determined by photolithography, avoiding the anisotropy and inhomogeneity problems of the oxidation process. The aperture has a wide controllable range (1-20μm), excellent repeatability and consistency, which is beneficial for improving mass production yield. Since no oxidation reaction is involved, the mechanical stress introduced by oxide layer volume shrinkage is completely eliminated, avoiding the generation and propagation of stress-induced defects, fundamentally solving the main reliability risks of oxidation-limited VCSELs.

[0011] Preferably, the thickness of the confinement layer is 50-200 nm.

[0012] Another objective of this application is to provide a method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser, employing the following technical solution: A method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser (VCSEL) includes the following steps: S1, first epitaxial growth, in which a buffer layer, an N-type DBR, an N-type cladding, an active region, a P-type cladding, and a confinement layer are sequentially grown on a substrate. S2. Photolithography patterning: Positive photoresist is coated on the surface of the confinement layer, and exposure is performed using contact lithography or step lithography. After development, a window pattern is formed in the center of the confinement layer. S3. Selective wet etching: using photoresist as a mask, selectively etch the confinement layer; remove Fe-doped AlGaAs within the window pattern to expose the underlying P-type cladding. S4, Second epitaxial growth, P-type DBR, contact layer and passivation layer.

[0013] By employing the above technical solution, a Fe-doped AlGaAs semi-insulating current-blocking layer is achieved: Fe, as a deep-level impurity, introduces a deeply dominant state into AlGaAs, pinning the Fermi level near the center of the band gap, thus making the material semi-insulating. Unlike traditional oxides, Fe-doped AlGaAs maintains the semiconductor lattice structure, without volume shrinkage or stress issues.

[0014] Preferably, the Fe doping concentration is 5 × 10⁻⁶ during the growth of the confinement layer in step S1. 17 -2×10 18 cm -3 .

[0015] By adopting the above technical solution, the Fe doping concentration is too low (<5×10⁻⁶). 17 cm -3 If the concentration is too high (>2×10), the semi-insulation is insufficient, resulting in poor current blocking effect; if the concentration is too high (>2×10), the insulation .... 18 cm -3 This may lead to a decrease in crystal quality and an increase in light absorption.

[0016] Preferably, ferrocene is used as the Fe source when growing the confinement layer in step S1.

[0017] Preferably, the V / III ratio is 10-30 when growing the confinement layer in step S1.

[0018] By adopting the above technical solution and using an appropriate V / III ratio, an atomically smooth regrowth interface with an interface roughness RMS < 0.5 nm can be obtained.

[0019] Preferably, in step S2, the diameter of the window graphic is greater than 3 μm and less than 10 μm.

[0020] By adopting the above technical solution, if the window diameter is too small (<3μm), the series resistance will increase and the optical loss will increase; if it is too large (>10μm), the tendency for multimode lasing will be enhanced.

[0021] In summary, this application includes at least one of the following beneficial technical effects: 1. Significantly improved device reliability: The absence of an oxidation stress field eliminates stress-induced dislocation propagation mechanisms, and the device lifetime is expected to be 2-5 times longer than that of traditional oxidation-limited devices.

[0022] 2. Optimized heat dissipation performance: The thermal conductivity of Fe-doped AlGaAs is about 8 times that of oxides, which effectively reduces the junction temperature and improves the device's performance in high-power and high-temperature (above 85°C) environments.

[0023] 3. Improved process controllability and yield: Photolithography defines the aperture to replace the time-sensitive oxidation process, with a wide process window and good batch-to-batch consistency, which is expected to improve mass production yield by 15-30%.

[0024] 4. Potential for increasing modulation bandwidth: Improved thermal characteristics can reduce thermally induced bandwidth roll-off, and combined with optimized epitaxial design, it is expected to achieve modulation bandwidth of >30GHz.

[0025] 5. Simplified equipment and reduced costs: No dedicated wet oxidation equipment is required; the entire process is completed within the MOCVD system, reducing equipment investment and process complexity. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1.

[0027] Explanation of reference numerals in the attached figures: 1. Substrate; 2. Buffer layer; 3. N-type DBR; 4. N-type cladding; 5. Active region; 6. P-type cladding; 7. Confinement layer; 8. P-type DBR; 9. Contact layer; 10. Passivation layer; 11. Light exit hole. Detailed Implementation

[0028] The present application will be further described in detail below with reference to all the accompanying drawings.

[0029] Example 1

[0030] This application discloses a non-oxidation-confined vertical-cavity surface-emitting laser, referring to... Figure 1 The structure comprises, from bottom to top, a substrate 1, a buffer layer 2, an N-type DBR 3, an N-type cladding layer 4, an active region 5, a P-type cladding layer 6, a confinement layer 7, a P-type DBR 8, a contact layer 9, and a passivation layer 10, wherein the material of the confinement layer 7 is Fe-doped AlGaAs. The thickness of the confinement layer 7 is 50-200 nm.

[0031] A circular light-emitting aperture 11 (current injection window) is fabricated at the center of the confinement layer 7 using a photolithography-wet etching process. The diameter of the light-emitting aperture 11 is within the optimal aperture range of 3-10 μm. This size can effectively avoid the problems of increased device series resistance and optical loss caused by small aperture (<3 μm), while avoiding the multimode lasing phenomenon caused by large aperture (>10 μm), ensuring that the device achieves stable single-mode laser output.

[0032] Compared to traditional oxide-confined VCSELs, this embodiment uses photolithography to precisely define the current window, resulting in extremely high consistency in window size and shape. It avoids the anisotropy and uneven oxidation defects inherent in the oxidation process, leading to excellent mass production repeatability. Furthermore, the entire process avoids high-temperature oxidation reactions, completely eliminating lattice mechanical stress caused by oxide layer volume shrinkage. This fundamentally prevents stress-induced lattice defects and dislocation propagation problems, significantly improving the long-term reliability of the device.

[0033] Fe atoms occupy Ga atom sites in the AlGaAs lattice. As a major impurity, they introduce characteristic energy levels within the band gap. The primary acceptor level is located 0.51 eV above the valence band top, and the secondary acceptor level is located 0.88 eV above the valence band top. In the N-type AlGaAs matrix, a carrier compensation reaction occurs: Fe... 3+ +e - →Fe 2+ It can completely compensate for the shallow background donor impurities generated by epitaxial growth, pinning the Fermi level to the center of the semiconductor band gap, making the confinement layer 7 exhibit stable semi-insulating properties, with a measured resistivity of up to 5 × 10⁻⁶. 8 Ω·cm can completely block the lateral current diffusion during device operation, enabling vertical directional current injection.

[0034] Meanwhile, the measured thermal conductivity of the Fe-doped AlGaAs confinement layer 7 in this embodiment is 18 W / (m·K), which is about 25 times higher than that of the aluminum oxide insulating layer of the traditional oxide confinement process (thermal conductivity 0.7 W / (m·K)). This can quickly dissipate the Joule heat and resonant heat loss generated during device operation, significantly reduce the device temperature rise, and ensure high-temperature operation stability.

[0035] Example 2

[0036] This application discloses a method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser (VCSEL), used in the non-oxidation-confined VCSEL described in the above embodiments, comprising the following steps. S1, First Epitaxial Growth The specific technical solution is as follows: An N-type GaAs substrate is placed in an MOCVD reaction chamber and heated to the growth temperature under a hydrogen atmosphere. An N-type DBR, N-type cladding, active region, P-type cladding, and confinement layer are grown sequentially. The confinement layer material is Fe-doped AlGaAs. The growth temperature of the confinement layer is 680-720°C, the V / III ratio is 10-30, ferrocene (Cp₂Fe) is used as the Fe source, and the Fe doping concentration is controlled at 5 × 10⁻⁶. 17 -2×10 18 cm -3 .

[0037] S2, Photolithography Patterning The specific technical solution is as follows: The epitaxial wafer is taken out from the MOCVD system, a positive photoresist (such as AZ5214) is coated on the surface of the Fe-doped AlGaAs layer, and exposure is performed by contact lithography or step lithography. After development, a circular opening pattern with a diameter of 3-10μm (corresponding to the current injection window) is formed.

[0038] S3, Selective Wet Etching The specific technical solution is as follows: Using photoresist as a mask, the Fe-doped AlGaAs layer is selectively etched using a mixed solution of citric acid and hydrogen peroxide (C6H8O7:H2O2:H2O=1:1:10). The etching depth is precisely controlled to the lower surface of the Fe-doped layer, completely removing the Fe-doped material in the window area and exposing the underlying P-type AlGaAs layer.

[0039] S4. Surface treatment and cleaning The specific technical solution is as follows: After etching, the photoresist is removed, and O2 plasma treatment is used for 30-60 seconds (power 50-100W) to remove residual organic matter and native oxides on the surface. Then, it is cleaned with diluted HCl solution (HCl:H2O=1:10) for 10-20 seconds, and finally rinsed with deionized water and dried with high-purity nitrogen. This surface treatment process can obtain an atomically smooth regrown surface.

[0040] S5, Second Epitaxial Growth The specific technical solution is as follows: The processed sample is rapidly transferred into the MOCVD reaction chamber. First, a thin p-type GaAs buffer layer is grown at a lower temperature (600-650°C) to repair the surface. Then, the temperature is increased to the normal growth temperature (680-720°C), and the p-type AlGaAs spacer layer and the upper p-DBR are grown sequentially. The regrowth rate is 1-3 μm / h to ensure interface smoothness and crystal quality.

[0041] S6. Device Fabrication The specific technical solution is as follows: After epitaxial growth is completed, a SiNx or SiO2 passivation layer is deposited, an electrode window is opened by photolithography and wet etching, and finally, P-type ohmic contact electrode (Ti / Pt / Au) and N-type ohmic contact electrode (AuGe / Ni / Au) are formed by evaporation and annealing.

[0042] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A non-oxidation-confined vertical-cavity surface-emitting laser, comprising, from bottom to top, a substrate (1), a buffer layer (2), an N-type DBR (3), an N-type cladding (4), an active region (5), a P-type cladding (6), a confinement layer (7), a P-type DBR (8), a contact layer (9), and a passivation layer (10), characterized in that: The confinement layer (7) is made of Fe-doped AlGaAs with a Fe doping concentration of 5 × 10⁻⁶. 17 -2×10 18 cm -3 The resistivity of the Fe-doped AlGaAs confinement layer (7) is 10. 7 -10 11 Ω·cm, thermal conductivity 10-25W / (m·K); confinement layer thickness 50-200nm; light-emitting hole (11) is formed in the center of confinement layer (7) by etching, and the diameter of light-emitting hole (11) is 3-10μm.

2. A method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser, characterized in that: The method for fabricating a non-oxidation confined vertical cavity surface-emitting laser as described in claim 1 includes the following steps: S1, first epitaxial growth, in which a buffer layer, an N-type DBR, an N-type cladding, an active region, a P-type cladding, and a confining layer are sequentially grown on a substrate; S2. Photolithography patterning: Positive photoresist is coated on the surface of the confinement layer, and exposure is performed using contact lithography or step lithography. After development, a window pattern is formed in the center of the confinement layer. S3. Selective wet etching: using photoresist as a mask, selectively etch the confinement layer; remove Fe-doped AlGaAs within the window pattern to expose the underlying P-type cladding. S4. Surface treatment and cleaning: After etching, remove the photoresist, treat with O2 plasma for 30-60 seconds to remove residual organic matter and native oxides on the surface, then clean with diluted HCl solution for 10-20 seconds, and finally rinse with deionized water and blow dry with high-purity nitrogen. S5, second epitaxial growth, P-type DBR, contact layer and passivation layer.

3. The method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser according to claim 2, characterized in that: In step S1, the Fe doping concentration is 5 × 10⁻⁶ during the growth of the confinement layer. 17 -2×10 18 cm -3 .

4. The method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser according to claim 2, characterized in that: In step S1, ferrocene is used as the Fe source when growing the confinement layer.

5. The method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser according to claim 2, characterized in that: In step S1, when growing the confinement layer, the V / III ratio is 10-30.

6. The method for fabricating a non-oxidation-confined vertical-cavity surface-emitting laser according to claim 2, characterized in that: In step S2, the diameter of the window graphic is greater than 3 μm and less than 10 μm.

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