Photonic crystal surface emitting laser based on heterogeneous integration and buried tunnel junction

Abstract

The application relates to the field of semiconductor lasers, and particularly discloses a photonic crystal surface emitting laser based on hetero-integration and a buried tunnel junction, which comprises a III-V semiconductor epitaxial layer and a low-refractive-index high-thermal-conductivity substrate (such as silicon carbide) hetero-integrated with the III-V semiconductor epitaxial layer, the epitaxial layer is provided with a photonic crystal structure composed of deep-etch air holes, the holes extend to the vicinity of a multi-quantum well active layer, and the photonic crystal surface emitting laser further comprises a buried tunnel junction (BTJ) structure for limiting current. The application enhances the light field restriction in the vertical direction through hetero-integration, effectively avoids interface defects caused by traditional secondary epitaxial filling, the high-thermal-conductivity characteristic of the silicon carbide substrate compensates for the heat dissipation deterioration caused by deep etching, and the buried tunnel junction structure concentrates current injection into the active area, thereby reducing the series resistance. The application can significantly improve the output power, mode stability and reliability of the laser under high-power working.

Description

Technical Field

[0001] This application relates to the field of semiconductor lasers, and in particular to a photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction. Background Technology

[0002] With the rapid development of fields such as optical communication, on-chip interconnects, lidar, and high-power coherent light sources, semiconductor lasers are evolving towards higher power, narrower linewidth, higher brightness, higher speed modulation, and easier integration. Photonic-Crystal Surface Emitting Lasers (PCSELs) utilize two-dimensional photonic crystal structures to provide in-plane distributed feedback, enabling coherent oscillation and vertical emission over a large area. They also possess high output power, narrow divergence angle, and good mode control capabilities, thus becoming a major research hotspot in high-performance semiconductor lasers in recent years.

[0003] In traditional PCSEL device structures, in order to enhance the interaction between the optical field and the photonic crystal and provide sufficient in-plane feedback, it is usually necessary to etch photonic crystal air holes or periodic refractive index modulation structures near the active region of the multiple quantum well (MQW). Then, the photonic crystal structure is buried in the semiconductor material through a secondary epitaxial process to restore the complete current injection and optical waveguide structure.

[0004] However, the traditional "etching + secondary epitaxy" fabrication process described above has significant technical bottlenecks and reliability risks. First, secondary epitaxy has stringent requirements for surface cleanliness, interface smoothness, and regrowth selectivity. The etched surface is highly susceptible to residual oxides and contaminants; if not properly treated, numerous defects will form at the regrowth interface, increasing not only optical absorption loss but also significantly raising the electrical series resistance. Second, when performing secondary epitaxy above periodic hole structures, problems such as hole closure or partial closure, poor uniformity of epitaxial layer coverage, and material defects are prone to occur, which can greatly interfere with the precise control of the laser's operating mode. Furthermore, the secondary epitaxy process significantly increases the complexity of the fabrication process and manufacturing costs. Maintaining extremely high consistency and cleanliness across photolithography, etching, cleaning, and regrowth steps requires very strict control over equipment conditions and process windows.

[0005] To circumvent the challenges of secondary epitaxial processes, some studies have attempted to replace secondary epitaxial filling with deep etching structures. However, deep etching presents new technical challenges: if the etching depth is insufficient, the photonic crystal structure is far from the active region, resulting in a weak overlap integral with the laser mode, leading to insufficient in-plane refractive index modulation, reduced coupling coefficient, and difficulty in forming low-loss oscillation modes; conversely, if the etching is too deep, the effective refractive index of the photonic crystal region is excessively reduced. Since traditional PCSELs typically use III-V group materials such as InP and GaAs as substrates, which have high refractive indices, the light field is prone to leak towards the high-refractive-index substrate after deep etching, resulting in reduced overlap between the mode field and the active region and a significant increase in radiation loss in the substrate direction.

[0006] On the other hand, in traditional electrically pumped PCSELs, the current injected into the structure typically diffuses laterally, making it difficult to concentrate it completely within the designated gain region. This leads to reduced current injection efficiency and increased threshold current. Simultaneously, current diffusion introduces additional series resistance and Joule heating, causing localized temperature rise, uneven gain distribution, and refractive index disturbances, severely impacting device performance. Furthermore, if the Joule heating and non-radiative recombination heat generated under large-area, high-power operating conditions cannot be dissipated quickly, it can lead to increased threshold current, output power roll-off, and decreased mode stability. Therefore, achieving efficient optical field confinement, good current confinement, and excellent heat dissipation performance simultaneously without relying on secondary epitaxial processes is a critical technical challenge that urgently needs to be addressed in the current PCSEL device design field. Summary of the Invention

[0007] To address the problems of complex secondary epitaxial processes, numerous interface defects, severe light field leakage to the substrate after deep etching, low injection efficiency due to lateral current diffusion, and poor heat dissipation in existing photonic crystal surface-emitting lasers, this application provides a photonic crystal surface-emitting laser based on heterogeneous integration and a buried tunnel junction.

[0008] This application provides a photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction, employing the following technical solution: A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction, comprising: III-V group semiconductor epitaxial layer, wherein the III-V group semiconductor epitaxial layer comprises at least a multi-quantum-well active layer; A photonic crystal structure, the photonic crystal structure including a deeply etched periodic air hole formed in the III-V group semiconductor epitaxial layer, the deeply etched periodic air hole extending downward to the vicinity of the multiple quantum well active layer; A low-refractive-index, high-thermal-conductivity substrate is heterogeneously integrated with the III-V group semiconductor epitaxial layer, wherein the refractive index of the low-refractive-index, high-thermal-conductivity substrate is lower than that of the III-V group semiconductor epitaxial layer, and the thermal conductivity is higher than that of the III-V group semiconductor epitaxial layer.

[0009] This application heterogeneously integrates a III-V group semiconductor epitaxial layer with a low-refractive-index, high-thermal-conductivity substrate. Utilizing the significant refractive index difference between the two, it effectively enhances the vertical optical field confinement and reduces light leakage towards the substrate, thereby improving the overlap integration efficiency between the optical field and the multi-quantum-well active region. Simultaneously, the high thermal conductivity substrate rapidly conducts heat generated in the active region to the outside, compensating for the localized heat dissipation degradation caused by deep-etched air holes, significantly reducing the device's thermal resistance and junction temperature. Furthermore, the deep-etched periodic air holes directly form a photonic crystal structure, avoiding the interface defects and process complexity caused by secondary epitaxial filling in traditional PCSELs. This ensures high in-plane refractive index modulation efficiency while improving device fabrication yield and long-term reliability.

[0010] Furthermore, the low refractive index and high thermal conductivity substrate is a silicon carbide substrate.

[0011] Silicon carbide has a thermal conductivity as high as 490 W·m -1 ·K -1 (Approximately 7 times that of traditional InP substrates and 10 times that of GaAs substrates), using silicon carbide as a low-refractive-index, high-thermal-conductivity substrate can significantly improve the overall heat dissipation efficiency of the laser. For electrically pumped PCSELs operating under large-area, high-power conditions, silicon carbide substrates can more quickly conduct Joule heating and non-radiative recombination heat from the junction region to the external heat sink, effectively suppressing threshold current drift and output power roll-off caused by heat accumulation. Simultaneously, silicon carbide itself is a medium-to-low refractive-index material, further optimizing the refractive index contrast between the III-V layer and the substrate, strengthening vertical optical confinement, enabling the laser to maintain excellent mode stability and optical conversion efficiency even at high power output.

[0012] Furthermore, the III-V semiconductor epitaxial layer includes, from bottom to top, a bottom N-type contact layer, a bottom N-type cladding layer, a multi-quantum-well active layer, a P-type cladding layer, a top N-type cladding layer, and a top N-type contact layer, wherein the low-refractive-index, high-thermal-conductivity substrate is heterogeneously integrated with the bottom N-type contact layer.

[0013] This layered structure allows the optical field to be strictly confined within the multi-quantum-well active layer between the two cladding layers. At the same time, the upper and lower double N-type contact layers, combined with the subsequent tunnel junction structure, can convert the traditional P-type contact into a low-resistance N-type contact, providing a reliable physical carrier from a material structure perspective for reducing the series resistance of the device, improving high-speed modulation performance and current injection efficiency.

[0014] Furthermore, the deeply etched periodic air holes sequentially penetrate the top N-type contact layer, the top N-type cladding layer, and the P-type cladding layer to the surface of the multi-quantum well active layer.

[0015] The deeply etched periodic air holes have a specific depth, ensuring that the air holes can generate sufficiently strong refractive index modulation. This allows for a full overlap between the in-plane feedback mode and the optical field distribution of the multi-quantum-well active layer, thereby significantly improving the bandgap modulation efficiency and surface emissivity of the photonic crystal. Simultaneously, the etching terminates on the upper surface of the multi-quantum-well active layer (rather than penetrating it), effectively avoiding damage to the quantum well material and non-radiative recombination of charge carriers caused by excessive etching, thus ensuring the crystal quality of the luminescent region.

[0016] Furthermore, the P-type cladding layer is provided with a buried tunnel junction structure, which is a highly doped PN junction, comprising an upper N-type layer and a lower P-type layer. The upper surface of the upper N-type layer is flush with the upper surface of the P-type cladding layer, and the upper surface of the upper N-type layer is in contact with the top N-type cladding layer.

[0017] The high doping concentration results in an extremely narrow PN junction barrier, allowing current to tunnel through and form a vertical path only in the buried tunnel junction (BTJ) region, effectively preventing lateral current diffusion in the P-type cladding. The "flush and contact" structural design ensures that electrons in the top N-type cladding can be injected vertically and without damage into the upper N-type layer of the BTJ, reducing ohmic losses and series resistance during current injection and significantly improving carrier injection uniformity.

[0018] Furthermore, the width of the buried tunnel structure in the transverse plane is smaller than the width of the area where the periodic air holes are distributed.

[0019] The width of the buried tunnel junction structure is smaller than that of the photonic crystal region, which precisely confines the injected current to the central region where the photonic crystal feedback is strongest, preventing current diffusion into the non-radiative region around the etched holes. This dual spatial matching structure of current confinement and mode confinement can significantly reduce the threshold current of the device and improve the differential quantum efficiency.

[0020] Furthermore, the width of the buried tunnel structure in the transverse plane is smaller than the width of the multi-quantum well active layer in the transverse plane.

[0021] The width of the buried tunnel structure is smaller than the width of the multi-quantum-well active layer, which ensures that the injected charge carriers are concentrated at the most effective location of stimulated emission, thereby maximizing the gain utilization efficiency of the active region.

[0022] Furthermore, it also includes an insulating layer, a top electrode, and a bottom electrode; The III-V semiconductor epitaxial layer has sidewalls, and the insulating layer covers the surface of the sidewalls; the top electrode is in contact with the top N-type contact layer; and the bottom electrode is in contact with the bottom N-type contact layer.

[0023] By adding an insulating layer to cover the sidewalls of the III-V semiconductor epitaxial layer, structural measures can effectively prevent short circuits or leakage currents caused by exposed mesa sidewalls, ensuring the enclosure of current injection in the active region and avoiding interference from parasitic capacitance and leakage channels on the high-frequency characteristics of the laser. Simultaneously, the top electrode contacts the top N-type contact layer, and the bottom electrode contacts the bottom N-type contact layer, forming a complete upper and lower electrical circuit. Furthermore, the double N-type contact layers combined with the buried tunnel junction structure lower the contact barrier, making the device's electrical performance more stable and reliable.

[0024] Furthermore, the photonic crystal structure includes a first region and a second region in the transverse plane. The deep etched air holes in the first region have a first lattice constant, and the deep etched air holes in the second region have a second lattice constant. The first lattice constant is different from the second lattice constant.

[0025] By dividing the photonic crystal structure into a first region and a second region with different lattice constants in the lateral plane, a dual heterogeneous photonic crystal cavity was structurally constructed. Since different lattice constants correspond to different photonic band gaps, after precise parameter design, the band edge modes of the first region can fall into the band gap of the second region. By utilizing the photonic band gap effect to generate lateral optical confinement, the optical mode field is localized in the first region, effectively suppressing the in-plane optical loss and lateral high-order modes that are prone to occur in traditional single-lattice photonic crystals. This significantly improves the edge mode suppression ratio and output beam quality of the laser, realizing stable surface emission with single-mode and high brightness.

[0026] This application also provides a method for fabricating a photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction, comprising the following steps: First epitaxy: A primary growth substrate is provided, and a top N-type contact layer, a top N-type cladding layer, and a buried tunnel junction layer are sequentially epitaxially formed on the primary growth substrate. The buried tunnel junction layer includes an upper N-type layer and a lower P-type layer sequentially formed on the top N-type cladding layer. Etched buried tunnel structure: The buried tunnel structure layer is patterned and etched until the top N-type cladding layer is exposed, forming a boss-shaped buried tunnel structure; Secondary epitaxy: A P-type cladding layer is epitaxially formed on the top N-type cladding layer, and the buried tunnel structure is buried in the P-type cladding layer; then, a multi-quantum well active layer, a bottom N-type cladding layer and a bottom N-type contact layer are epitaxially formed sequentially on the P-type cladding layer; Bonding: The semiconductor structure that has completed secondary epitaxy is inverted, and the bottom N-type contact layer is bonded to a substrate with low refractive index and high thermal conductivity; then the original growth substrate is removed to expose the surface of the top N-type contact layer; Deep etching: Deep etching is performed on the bonded semiconductor structure to form deep etched periodic air holes. The deep etched periodic air holes sequentially penetrate the top N-type contact layer, the top N-type cladding layer, and the P-type cladding layer to the surface of the multi-quantum well active layer. Etching the laser mesa and fabricating electrodes.

[0027] This fabrication method avoids the interface contamination, hole closure, and defect problems caused by secondary epitaxy filling above the photonic crystal etching holes in traditional PCSELs by following the process sequence of "first fabricating a buried tunnel junction and completing secondary epitaxy, then inverting and bonding a heterogeneous substrate, and finally deeply etching the photonic crystal." This reduces the complexity of the fabrication process. After the first epitaxy, the tunnel junction thin layer is patterned and etched to form protrusions, and then a P-type cladding layer is grown using secondary epitaxy to completely bury it. This etching-then-burying sequence ensures that the buried tunnel junction structure can be flatly and precisely embedded in the P-type cladding layer, ensuring that subsequent current can tunnel vertically only along the designed buried tunnel junction structure region, providing structural protection for low-resistance and high-efficiency current injection.

[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. This application heterobonds a III-V group epitaxial layer to a low-refractive-index, high-thermal-conductivity silicon carbide substrate and deeply etches a photonic crystal above the multi-quantum-well active layer, constructing a high-refractive-index step in the vertical direction. This effectively localizes the optical mode field within the multi-quantum-well active layer, reducing the leakage loss of the optical field towards the substrate caused by insufficient refractive index difference in traditional deep-etched structures. Simultaneously, the silicon carbide substrate has extremely high thermal conductivity, enabling rapid conduction of Joule heat and non-radiative recombination heat generated in the active region to the external heat sink. This design effectively compensates for the localized heat dissipation degradation caused by deep-etched air holes, significantly reducing the device's thermal resistance and junction temperature, thereby ensuring the output stability and reliability of the laser under high-power, continuous operation conditions.

[0029] 2. This application employs a deep-etched air-hole structure independent of secondary epitaxy. A significant effective refractive index difference is generated between the air-hole region and the non-etched region, resulting in a substantial increase in the bandgap opening of the photonic crystal, thus significantly enhancing in-plane refractive index modulation efficiency and distribution feedback. By designing dual heterogeneous photonic crystal cavities with different lattice constants, the optical mode field can be precisely localized within the target gain region using the photonic bandgap effect, reducing in-plane optical losses. Furthermore, the introduced buried tunnel junction (BTJ) structure, through the tunneling effect of a highly doped reverse-biased PN junction, strictly limits the injected current to a preset gain region, effectively avoiding current congestion and increased series resistance caused by lateral current diffusion. Simultaneously, the traditional P-type contact is converted to an N-type contact to reduce contact resistance, thereby significantly improving current injection efficiency, suppressing parasitic Joule heating, and lowering the device's threshold current.

[0030] 3. Compared to the complex process of traditional PCSELs requiring secondary epitaxy above etched vias to restore the waveguide structure, this application places the deep etching operation after bonding and removal of the original substrate. This design avoids the technical challenges that easily occur during secondary epitaxy on etched vias, such as interface defects, uneven via closure, material contamination, and poor uniformity. It reduces the complexity of the fabrication process and the stringent requirements on the process window, thereby improving device yield and giving the laser superior long-term operational stability. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of a photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction, according to Embodiment 1 of this application. Figure 2 (a) is the simulated longitudinal section mode field distribution diagram, and (b) is the longitudinal mode field distribution of the device and the corresponding material refractive index distribution diagram. Figure 3 In the diagram, (a) is the cross-sectional distribution of the dual heterogeneous photonic crystal resonator, (b) is the band diagram, and (c) is the mode field distribution diagram. Figure 4 This is a flowchart of a method for fabricating a photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction, as described in Embodiment 2 of this application.

[0032] Reference numerals: 1. Bottom N-type contact layer; 2. Bottom N-type cladding layer; 3. Multi-quantum well active layer; 4. P-type cladding layer; 5. Top N-type cladding layer; 6. Top N-type contact layer; 7. Low refractive index, high thermal conductivity substrate; 8. Buried tunnel junction structure; 9. Upper N-type layer of buried tunnel junction; 10. Lower P-type layer of buried tunnel junction; 11. Deeply etched periodic air holes; 12. Insulating layer; 13. Top electrode; 14. Bottom electrode. Detailed Implementation

[0033] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0034] Example 1 This application discloses a photonic crystal surface-emitting laser based on heterogeneous integration and a buried tunnel junction. (Refer to...) Figure 1 The photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction includes a low-refractive-index, high-thermal-conductivity substrate 7 (preferably a silicon carbide substrate in this embodiment) and a III-V group semiconductor epitaxial layer bonded to the silicon carbide substrate.

[0035] Specifically, the III-V semiconductor epitaxial layer, from bottom to top (with reference to the orientation after bonding), includes the following: Bottom N-type contact layer 1, the material is highly doped N. + -InP, used for contact with bottom electrode 14; The bottom N-type coating layer 2, made of N-InP, serves as the lower light confinement layer. The active layer 3, made of InGaAsP or AlGaInAs multi-quantum-well structure, provides optical gain. P-type coating layer 4, made of P-InP, serves as the upper light confinement layer and hole transport layer; A buried tunnel junction structure 8 is disposed inside the P-type cladding layer 4. The buried tunnel junction structure 8 is a highly doped reverse PN junction, including an upper N-type layer 9 (N... + -InP) and buried tunnel substructure P-type layer 10 (P + -InP); The width of the buried tunnel structure 8 in the transverse plane is smaller than the width of the multi-quantum well active layer 3, and the upper surface of the upper N-type layer 9 of the buried tunnel structure is flush with the upper surface of the P-type cladding layer 4. The top N-type cladding layer 5, made of N-InP, is located above the P-type cladding layer 4 and is in contact with the upper N-type layer 9 of the buried tunnel structure. The top N-type contact layer 6, made of N+-InP, is located above the top N-type coating layer 5 and is used to contact the top electrode 13.

[0036] A photonic crystal structure is disposed in the epitaxial layer of a III-V semiconductor. The photonic crystal structure consists of deeply etched periodic air holes 11 formed on the upper part of the epitaxial layer. The deeply etched periodic air holes 11 sequentially penetrate the top N-type contact layer 6, the top N-type cladding layer 5, and the P-type cladding layer 4, and terminate at the surface of the multi-quantum-well active layer 3. The deeply etched periodic air holes 11 are filled with air, forming a large refractive index difference with the surrounding semiconductor material, which is used to provide in-plane periodic modulation of the refractive index.

[0037] In the vertical direction, this embodiment employs a dual constraint on the optical mode: first, the III-V epitaxial layer is bonded to a silicon carbide substrate with medium refractive index and high thermal conductivity; second, a deep etching process is used to stop the periodic air holes of the photonic crystal above the multi-quantum-well active layer 3.

[0038] Compared to using traditional III-V substrates such as InP or GaAs directly, this embodiment uses silicon carbide as a highly efficient heat dissipation channel, which can quickly conduct the heat generated in the gain region to the external heat sink, effectively reducing the thermal resistance and junction temperature of the device, thereby compensating for the deterioration of heat dissipation performance caused by the formation of air gaps due to deep etching of air holes.

[0039] Meanwhile, silicon carbide has a relatively low refractive index, which increases the refractive index contrast between the multi-quantum-well active layer 3 and the substrate, allowing the light field to be more highly localized within the multi-quantum-well active layer 3 in the vertical direction. Device simulation results verify the effectiveness of the above structural design: Figure 2 As shown in (a), the longitudinal mode field distribution is almost completely concentrated in the multi-quantum well active layer 3, with almost no mode field leaking towards the substrate, which significantly reduces substrate loss. Figure 2 Figure (b) shows the longitudinal mode field distribution and refractive index distribution. The left y-axis represents the normalized electric field, and the right y-axis represents the refractive index settings of each layer in the longitudinal direction of the simulated device. It can be seen that the multi-quantum well active layer 3 has a good refractive index contrast with other layers, thus concentrating most of the mode field in the multi-quantum well active layer 3. Therefore, it can be seen that the heterobonding and deep etching design of this application have a synergistic effect in enhancing vertical optical field confinement and suppressing substrate leakage.

[0040] To further reduce in-plane losses, such as Figure 3 As shown in (a), the photonic crystal structure is divided into a first region (region A) and a second region (region B) with different lattice constants in the transverse plane to form a dual heterogeneous photonic crystal cavity. Since different lattice constants correspond to different photonic band gaps, after precise parameter design, the band edge mode of region A can fall within the band gap of region B, as shown in (a). Figure 3 As shown in (b); the photonic bandgap effect is used to generate lateral optical confinement, localizing the optical mode field in region A, as shown in (b). Figure 3 As shown in (c) in the figure.

[0041] Regarding current injection and confinement, this embodiment achieves effective control of the current transport region by setting a buried tunnel junction (BTJ) structure within the P-type cladding layer 4. This BTJ structure transforms the traditional P-type contact into an N-type contact. In operation, the peripheral region of the BTJ structure is under reverse bias, where charge carriers are effectively blocked by the potential barrier and cannot pass through. However, in the local region where the BTJ structure is located, although it also experiences reverse bias, its highly doped PN junction significantly compresses the depletion layer width to an extremely narrow range due to the high doping concentration. This triggers quantum tunneling of charge carriers (electrons) under reverse bias, forming a localized conductive channel. Figure 1 The arrows in the diagram indicate the direction of the current. Based on the above mechanism, the injected current is strictly confined to the micro-region defined by the BTJ aperture, effectively preventing the lateral diffusion of current within the multi-quantum-well active region, thereby achieving concentrated and uniform injection of charge carriers.

[0042] In addition, the laser includes an insulating layer 12 and electrodes. The III-V semiconductor epitaxial layer has sidewalls covered with a silicon dioxide insulating layer 12 to prevent current leakage along the sidewalls. A top electrode 13 is deposited within an electrode window on the surface of the top N-type contact layer 6; a bottom electrode 14 is deposited within an electrode window on the surface of the bottom N-type contact layer 1.

[0043] Example 2 This embodiment provides a specific fabrication method for the aforementioned laser, the process flow of which is as follows: Figure 4 As shown, the specific steps include: First epitaxy: A primary growth substrate is provided, including an InP substrate and an InP buffer layer formed on the InP substrate. Using a metal-organic chemical vapor deposition (MOCVD) process, a top N-type contact layer, a top N-type cladding layer, and a buried tunnel junction layer are sequentially epitaxially formed on the InP buffer layer of the primary growth substrate. The buried tunnel junction layer includes an upper N-type layer and a lower P-type layer sequentially formed on the top N-type cladding layer.

[0044] Etched Buried Tunnel Junction Structure: An etching mask is formed on the surface of the buried tunnel junction layer using photolithography. Dry or wet etching is then employed to pattern the buried tunnel junction layer until the underlying top N-type cladding layer is exposed, forming a boss-shaped buried tunnel junction structure. The lateral width of the buried tunnel junction structure is smaller than the width of the subsequent active region and also smaller than the width of the periodic air hole distribution area in the subsequent deep etching.

[0045] Secondary epitaxy: After removing the photolithography mask, MOCVD process is used again to epitaxially form a P-type cladding layer on the top N-type cladding layer, burying the buried tunnel junction structure in the P-type cladding layer; then, a multi-quantum well active layer, a bottom N-type cladding layer and a bottom N-type contact layer are epitaxially formed sequentially on the P-type cladding layer.

[0046] Bonding: The semiconductor structure that has completed secondary epitaxy is inverted (with the bottom N-type contact layer facing down), and the bottom N-type contact layer is bonded to the silicon carbide substrate with low refractive index and high thermal conductivity; wet etching is used to remove the original InP growth substrate, exposing the surface of the top N-type contact layer.

[0047] Deep via etching: Electron beam photoresist is spin-coated onto the exposed top N-type contact layer surface. Periodic photolithographic patterns of the photonic crystal are formed through electron beam exposure and development. Using an ICP etching system, deep etching is performed using the photoresist as a mask to form deeply etched periodic air holes. The etching time and depth are precisely controlled so that the deeply etched periodic air holes sequentially penetrate the top N-type contact layer, the top N-type cladding layer, the P-type cladding layer, and finally to the surface of the multi-quantum well active layer.

[0048] Etching the laser mesa and fabricating electrodes: The mesa region exposing the bottom N-type contact layer is etched using photolithography and ICP etching. A silicon dioxide insulating layer is then deposited to cover the mesa sidewalls, and electrode contact regions are formed on the surfaces of the bottom and top N-type contact layers using photolithography. Finally, metal electrodes are deposited in the electrode contact regions and rapidly annealed to form ohmic contacts, ultimately obtaining the laser of this application.

[0049] 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 photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction, characterized in that: include: III-V group semiconductor epitaxial layer, wherein the III-V group semiconductor epitaxial layer comprises at least a multi-quantum-well active layer; A photonic crystal structure, the photonic crystal structure including a deeply etched periodic air hole formed in the III-V group semiconductor epitaxial layer, the deeply etched periodic air hole extending downward to the vicinity of the multiple quantum well active layer; A low-refractive-index, high-thermal-conductivity substrate is heterogeneously integrated with the III-V group semiconductor epitaxial layer, wherein the refractive index of the low-refractive-index, high-thermal-conductivity substrate is lower than that of the III-V group semiconductor epitaxial layer, and the thermal conductivity is higher than that of the III-V group semiconductor epitaxial layer.

2. The photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 1, characterized in that: The low-refractive-index, high-thermal-conductivity substrate is a silicon carbide substrate.

3. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 1, characterized in that: The III-V semiconductor epitaxial layer includes, from bottom to top, a bottom N-type contact layer, a bottom N-type cladding layer, a multi-quantum-well active layer, a P-type cladding layer, a top N-type cladding layer, and a top N-type contact layer, wherein the low-refractive-index, high-thermal-conductivity substrate is heterogeneously integrated with the bottom N-type contact layer.

4. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 3, characterized in that: The deeply etched periodic air holes sequentially penetrate the top N-type contact layer, the top N-type cladding layer, and the P-type cladding layer to the surface of the multi-quantum well active layer.

5. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 4, characterized in that: The P-type cladding layer contains a buried tunnel junction structure, which is a highly doped PN junction. It includes an upper N-type layer and a lower P-type layer. The upper surface of the upper N-type layer is flush with the upper surface of the P-type cladding layer, and the upper surface of the upper N-type layer is in contact with the top N-type cladding layer.

6. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 5, characterized in that: The width of the buried tunnel structure in the transverse plane is smaller than the width of the area where the periodic air holes are distributed.

7. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 6, characterized in that: The width of the buried tunnel structure in the transverse plane is smaller than the width of the multi-quantum well active layer in the transverse plane.

8. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 3, characterized in that: It also includes an insulating layer, a top electrode, and a bottom electrode; The III-V semiconductor epitaxial layer has sidewalls, and the insulating layer covers the surface of the sidewalls; the top electrode is in contact with the top N-type contact layer; The bottom electrode is in contact with the bottom N-type contact layer.

9. A photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in claim 1, characterized in that: The photonic crystal structure includes a first region and a second region in a transverse plane. Deeply etched air holes in the first region have a first lattice constant, and deeply etched air holes in the second region have a second lattice constant. The first lattice constant is different from the second lattice constant.

10. A method for fabricating a photonic crystal surface-emitting laser based on heterogeneous integration and buried tunnel junction as described in any one of claims 1-9, characterized in that: Includes the following steps: First epitaxy: A primary growth substrate is provided, and a top N-type contact layer, a top N-type cladding layer, and a buried tunnel junction layer are sequentially epitaxially formed on the primary growth substrate. The buried tunnel junction layer includes an upper N-type layer and a lower P-type layer sequentially formed on the top N-type cladding layer. Etched buried tunnel structure: The buried tunnel structure layer is patterned and etched until the top N-type cladding layer is exposed, forming a boss-shaped buried tunnel structure; Secondary extension: A P-type cladding layer is formed on the top N-type cladding layer, and the buried tunnel structure is buried in the P-type cladding layer; Then, a multi-quantum-well active layer, a bottom N-type cladding layer, and a bottom N-type contact layer are sequentially epitaxially formed on the P-type cladding layer. Bonding: The semiconductor structure that has completed secondary epitaxy is inverted, and the bottom N-type contact layer is bonded to a substrate with low refractive index and high thermal conductivity; then the original growth substrate is removed to expose the surface of the top N-type contact layer; Deep etching: Deep etching is performed on the bonded semiconductor structure to form deep etched periodic air holes. The deep etched periodic air holes sequentially penetrate the top N-type contact layer, the top N-type cladding layer, and the P-type cladding layer to the surface of the multi-quantum well active layer. Etching the laser mesa and fabricating electrodes.

Images