Vertical cavity surface emitting laser with defect isolation region

Abstract

The application discloses a vertical cavity surface emitting laser with a defect isolation area, comprising an active region platform, wherein the active region platform comprises, from bottom to top, a partial first DBR layer, an active layer, an oxidation limiting layer and a second DBR layer; a defect isolation area is arranged in the second DBR layer, wherein the defect isolation area comprises a vertical groove close to the edge of the active region platform and surrounding the central area of the active region platform, the projection of the vertical groove in the horizontal direction is in a closed shape, and the vertical groove is filled with a high-thermal-conductivity ceramic material. Compared with the prior art, the application can effectively isolate the surface defect recombination center of the side surface of the active region platform formed in the etching process and the sidewall oxidation process, thereby effectively improving the performance and reliability of the laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to a vertical-cavity surface-emitting laser (VCSEL). Background Technology

[0002] Vertical-cavity surface-emitting lasers (VCSELs) possess high optical power and excellent transverse mode control, making them highly promising for applications in optical communication, attitude sensing sensors, printing, and magnetic storage. However, their structure suffers from drawbacks such as a thin active region, short cavity length, and low single-layer gain. To improve their effective photon confinement capability, oxide-confined structures are currently widely used. The oxide aperture formed by the oxide-confined structure provides excellent transverse confinement of the current injected into the active region, resulting in virtually no transverse current. Simultaneously, this oxide aperture structure can also transversely confine the light emitted from the laser's active region, reducing the number of laser modes. This mode reduction effectively stabilizes the laser.

[0003] In the current process of fabricating oxide-limited VCSELs, it is necessary to first prepare an epitaxial wafer (including a substrate and an epitaxial layer, the epitaxial layer consisting of alternating Al layers). x Ga 1-x The process involves etching an As and GaAs layer to form an active region platform consisting of a first DBR layer, an active layer, and a second DBR layer arranged sequentially from bottom to top. Then, the high-aluminum Al content in the second DBR layer near the active layer is etched. x Ga 1-x The As layer undergoes sidewall oxidation, resulting in a high-aluminum-content Al layer. x Ga 1-x The outer periphery of the As layer is oxidized while the central region remains unoxidized, thus forming an oxidation-confined structure with oxidation pores in the center.

[0004] The etching process described above will create a large number of defects on the sidewalls and bottom of the active region platform. These defects are prone to forming a large number of surface defect recombination centers, which are channels for laser leakage and will affect the performance and reliability of the laser. The sidewall oxidation process described above will form a large number of oxides on the surface of the active region platform sidewall. These oxides are unstable and in a non-stoichiometric state, which further aggravates the generation of surface defect recombination centers, worsens the laser leakage problem, and ultimately further affects the performance and reliability of the laser.

[0005] In addition to the high-alumina layer being oxidized during the sidewall oxidation process, the DBR layer above the active layer also has a lower aluminum content (Al). x Ga 1-x The As layer will also be oxidized, and the length of the oxidized layer is generally 1-3 μm. Figure 1This diagram shows a typical structure of an existing oxide-confined VCSEL, comprising: a GaAs substrate 1, a buffer layer 2, an N-type DBR layer 3, a quantum well active layer 4, a P-type DBR layer 5, an oxide confinement layer 7, a dielectric protective layer 9, a P-type metal 10, and an N-type metal 11; as shown. Figure 1 As shown, the upper part of the P-type DBR layer 5 has a low aluminum content (Al). x Ga 1-x The outer edge of the As layer is also oxidized during the sidewall oxidation process, forming a low-aluminum oxide layer. 8. The oxidation of the low-aluminum layer not only causes changes in the structure of the DBR layer on the outer side of the active platform, but also generates significant stress, affecting the laser's performance and reliability. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a vertical cavity surface-emitting laser with a defect isolation region, which can effectively isolate the surface defect recombination center on the side of the active region platform formed during the etching process and the sidewall oxidation process, thereby effectively improving the performance and reliability of the laser.

[0007] The present invention proposes a vertical cavity surface-emitting laser with a defect isolation region, comprising an active region platform. The active region platform includes, from bottom to top, a partial first DBR layer, an active layer, an oxide confinement layer, and a second DBR layer. A defect isolation region is provided in the second DBR layer. The defect isolation region includes a vertical groove near the edge of the active region platform and surrounding the central region of the active region platform. The projection of the vertical groove in the horizontal direction is closed. The vertical groove is filled with a high thermal conductivity ceramic material.

[0008] Furthermore, before filling the high thermal conductivity ceramic material, the inner wall surface of the vertical groove is treated with trimethylaluminum (TMA). The specific method is as follows: at a treatment temperature of 250-350 °C and a treatment pressure of 50-500 Pa, the following cycle treatment is performed several times: first, trimethylaluminum is introduced into the reaction chamber for 5-60 s, and then nitrogen is introduced for 5-60 s.

[0009] Furthermore, prior to the trimethylaluminum surface treatment, the active zone platform with the vertical grooves undergoes heat treatment under a nitrogen-protected environment at a temperature of 250-350 °C for 30-60 min. Alternatively, prior to the trimethylaluminum surface treatment, the active region platform with the vertical grooves undergoes hydrogen heat treatment, specifically as follows: the active region platform with the vertical grooves is heat-treated in a hydrogen atmosphere at a temperature of 350-500°C for 15-30 minutes.

[0010] Furthermore, before filling the high thermal conductivity ceramic material, the active region platform with the vertical grooves is subjected to hydrogen heat treatment. The specific method is as follows: the active region platform with the vertical grooves is heat treated in a hydrogen atmosphere at a temperature of 350-500℃ for a time of 25-40 min.

[0011] Preferably, the vertical groove has the same horizontal projection shape as the active area platform.

[0012] Preferably, the horizontal distance between the vertical groove and the edge of the active area platform is 0.5 μm - 3 μm.

[0013] Preferably, the high thermal conductivity ceramic material is any one of the following materials: AlN, AlCrN, CrN, TiN, TiAlN, TaN, SiC.

[0014] Preferably, the defect isolation region is formed before the formation of the oxide confinement layer.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention improves the active region platform structure of existing oxide-limited VCSELs by setting a defect isolation region filled with a high thermal conductivity ceramic material in the second DBR layer above the oxide-limited layer. This effectively isolates the surface defect recombination center on the side of the active region platform formed during the etching process and sidewall oxidation process. At the same time, it can effectively conduct the heat generated during laser use away from the laser, thereby significantly improving the laser performance and reliability. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of an existing oxidation-limited VCSEL. Figure 2 This is a schematic cross-sectional view of the VCSEL with a defect isolation region according to the present invention. Figures 3 to 15 for Figure 2 The diagram shows a process diagram of one fabrication technology for VCSEL.

[0017] The meanings of the reference numerals appearing in the figure are as follows: 1. GaAs substrate; 2. Buffer layer; 3. N-type DBR layer; 4. Quantum well active layer; 5. P-type DBR layer; 6. Defect isolation region; 7. Oxidation confinement layer; 8. Oxidized portion of low-aluminum layer; 9. Dielectric protection layer; 10. P-type metal; 11. N-type metal. Implementation

[0018] To address the shortcomings of existing technologies, the present invention improves the active region platform structure of existing oxide-limited VCSELs by setting a defect isolation region filled with a highly thermally conductive ceramic material in the second DBR layer above the oxide-limited layer. This effectively isolates the surface defect recombination center formed on the active region platform surface during the etching process and sidewall oxidation process, and at the same time effectively conducts the heat generated during laser use away from the laser, thereby significantly improving the laser performance and reliability.

[0019] Specifically, the vertical cavity surface-emitting laser with a defect isolation region proposed in this invention includes an active region platform. The active region platform includes a first DBR layer, an active layer, an oxide confinement layer, and a second DBR layer arranged sequentially from bottom to top. A defect isolation region is provided in the second DBR layer. The defect isolation region includes a vertical groove near the edge of the active region platform and surrounding the central region of the active region platform. The projection of the vertical groove in the horizontal direction is a closed shape. The vertical groove is filled with a high thermal conductivity ceramic material.

[0020] The vertical groove and the active area platform can have the same or different projection shapes in the horizontal direction; preferably, the vertical groove and the active area platform have the same projection shape in the horizontal direction.

[0021] Preferably, the horizontal distance between the vertical groove and the edge of the active area platform is 0.5 μm - 3 μm.

[0022] The reason this invention uses a high thermal conductivity ceramic material as the filler in the defect isolation region is because it possesses characteristics such as chemical stability, low coefficient of thermal expansion, good thermal conductivity, and high temperature resistance. Its chemical stability ensures that the material can directly contact GaAs without undergoing a chemical reaction; its low coefficient of thermal expansion prevents volume expansion due to heat; its good thermal conductivity allows for timely conduction of heat generated by the laser; and its high temperature resistance meets the requirements of potentially high-temperature processes during fabrication. Preferably, the high thermal conductivity ceramic material is any one of the following: AlN, AlCrN, CrN, TiN, TiAlN, TaN, or SiC.

[0023] During the formation of the defect isolation region, the epitaxial layer needs to be etched to form vertical trenches. This process also generates some defects and unstable underoxides (such as AsO) on the inner surface of the vertical trenches. x GaO x (etc.), and at the same time, some stress will be generated, which will weaken the performance and reliability improvement brought about by the defect isolation area to a certain extent.

[0024] To address the aforementioned issues, the inner wall surface of the vertical trench is further treated with trimethylaluminate (TMA) before filling with the high thermal conductivity ceramic material. The specific method is as follows: At a treatment temperature of 250-350 °C and a treatment pressure of 50-500 Pa, several cycles of the following treatment are performed: first, trimethylaluminate is introduced into the reaction chamber for 5-60 s, followed by nitrogen gas for 5-60 s. TMA treatment effectively removes unstable underoxides from the surface of the defect isolation steps. Removal of these underoxides reduces leakage current during laser operation, improving laser performance and reliability.

[0025] Furthermore, prior to the trimethylaluminum surface treatment, the active zone platform with the vertical grooves undergoes heat treatment under a nitrogen-protected environment at a temperature of 250-350 °C for 30-60 min. Alternatively, prior to the trimethylaluminum surface treatment, the active region platform with the vertical grooves undergoes hydrogen heat treatment, specifically as follows: the active region platform with the vertical grooves is heat-treated in a hydrogen atmosphere at a temperature of 350-500°C for 15-30 minutes. This heat treatment helps eliminate the structural stress caused by the etching of the vertical grooves.

[0026] Alternatively, the following approach can be used to replace the combination of TMA treatment and (nitrogen or hydrogen) heat treatment to achieve a similar effect: before filling the high thermal conductivity ceramic material, the active region platform with the vertical grooves is subjected to hydrogen heat treatment, specifically as follows: the active region platform with the vertical grooves is heat treated in a hydrogen atmosphere at a temperature of 350-500℃ for 25-40 minutes.

[0027] The defect isolation region can be formed before or after the sidewall oxidation process; preferably, the defect isolation region is formed before the formation of the oxide confinement layer. In this way, the formed defect isolation region can effectively isolate the surface defect recombination centers on the active region platform surface formed during the etching and sidewall oxidation processes, effectively conducting the heat generated during laser use away from the laser. Furthermore, it can effectively control the oxidation of the low-aluminum layer during the sidewall oxidation process, reducing the length of the oxidized portion of the low-aluminum layer and mitigating the stress impact caused by the oxidation of the low-aluminum layer.

[0028] To facilitate public understanding, the technical solution of the present invention will be further described in detail below through a specific embodiment and in conjunction with the accompanying drawings: The VCSEL with defect isolation region in this embodiment is... Figure 1 It is an improvement based on the VCSEL shown, and its structure is as follows: Figure 2 As shown, compared to Figure 1 The VCSEL shown differs in that its P-type DBR layer 5 has a defect isolation region 6. The defect isolation region 6 includes a vertical groove near the edge of the active region platform and surrounding the center of the active region platform. The projection of the vertical groove in the horizontal direction is a closed shape (in this embodiment, it is a ring concentric with the cylindrical active region platform). The vertical groove is filled with high thermal conductivity ceramic materials such as AlN, AlCrN, CrN, TiN, TiAlN, TaN, and SiC.

[0029] Figure 2 The VCSEL shown has a defect isolation region and can be used in Figure 1 The VCSEL shown is fabricated using existing mature semiconductor manufacturing processes. One preferred fabrication process is given below: Step 1: The cross-section of the epitaxial wafer selected in this embodiment is as follows. Figure 3 As shown, the structure includes, from bottom to top, a GaAs substrate, a buffer layer, an N-type DBR layer, a quantum well active layer, and a P-type DBR layer; photoresist is coated on the surface of the epitaxial wafer, with a photoresist film thickness of 1-5 μm; the photoresist is exposed and developed to obtain a defect isolation region pattern without photoresist coverage. The defect isolation region pattern is ring-shaped. See [reference needed]. Figure 4 In this embodiment, the width of the defect isolation area pattern is 0.5-3µm, which can be adjusted appropriately according to the actual size of the laser. Step 2: Use ICP dry etching to etch the epitaxial wafer obtained in Step 1. The etching gas is Cl2 / BCl3 or Cl2 / SiCl4. Etching is stopped when 1-5 pairs of P-DBRs are above the quantum well active layer. Remove the photoresist to obtain a circular vertical trench. See [link to relevant documentation]. Figure 5 ; Step 3: Heat-treat the epitaxial wafer with the annular vertical groove structure obtained in Step 2. The heat treatment is carried out in the same chamber as the ALD equipment. The heat treatment temperature is 250-350℃, the heat treatment atmosphere is nitrogen, and the time is 30-60 minutes. Step 4: Subsequently, the epitaxial wafer completed in Step 3 undergoes annular vertical groove surface treatment using trimethylaluminum. The surface treatment temperature is the same as the heat treatment temperature within the same chamber, and the surface treatment pressure is 50-500 Pa. The trimethylaluminum surface treatment consists of multiple cycles. One surface treatment cycle consists of the following two steps: first, trimethylaluminum is introduced for 5-60 seconds, then the TMA introduction is stopped, followed by nitrogen gas introduction for 5-60 seconds, and then nitrogen gas introduction is stopped. Generally, 3-5 surface treatment cycles are selected. See [link to relevant documentation]. Figure 6 ; Step 5: Deposit a high thermal conductivity ceramic material on the surface of the epitaxial wafer after the surface treatment in Step 4 to fill the annular vertical trench. In this embodiment, the deposition of the high thermal conductivity ceramic material and the TMA surface treatment are performed in different chambers of the same equipment. After the TMA surface treatment, the epitaxial wafer only needs to be transferred to the sputtering deposition chamber in a vacuum environment to perform the deposition of the high thermal conductivity ceramic material. The deposition method is radio frequency sputtering, with a sputtering power of 50-200W, a sputtering pressure of 0.1-0.5Pa, and an Ar / N2 mixed gas as the sputtering gas. The preferred high thermal conductivity ceramic material is AlN, whose thermal conductivity is more than ten times that of GaAs, which can better conduct heat. The epitaxial wafer after the high thermal conductivity ceramic material deposition is as follows: Figure 7 As shown; Step 6: Remove the high thermal conductivity ceramic material from the surface of the epitaxial wafer obtained in Step 5, retaining only the high thermal conductivity ceramic material filling the annular vertical trenches. This completes the preparation of the defect isolation region. In this embodiment, the high thermal conductivity ceramic material removal method is ICP etching, with Cl2+Ar as the etching gas, an etching power of 20-50W, and an etching pressure of 0.5-5Pa. The completed epitaxial wafer is shown below. Figure 8 As shown; Step 7: Coat the epitaxial wafer surface completed in Step 6 with photoresist. The photoresist film thickness is 2-10µm, ensuring that only the active region platform area is covered with photoresist, while the remaining areas are unretained. The defect isolation area is concentric with the photoresist on the active region platform, and is located below the photoresist on the active region platform and covered by photoresist. The distance 'a' between the edge of the photoresist on the active region platform and the defect isolation area is 0.5-3µm. See [link to relevant documentation]. Figure 9 ; Step 8: Apply ICP dry etching to the epitaxial wafer completed in Step 7. The etching gas is Cl2 / BCl3 or Cl2 / SiCl4. Etch until the N-DBR layer 1-10 below the quantum well layer is reached, then stop etching. See [link to relevant documentation]. Figure 10 ; Remove the photoresist to obtain an active region platform structure with defect isolation areas, such as Figure 11 As shown; Step 9: Perform wet sidewall oxidation on the active region platform obtained in Step 8 to obtain an active region platform with an oxidation confinement layer; as shown... Figure 12 As shown, the wet oxidation process will reduce the aluminum content of Al... x Ga 1-x Al oxidation occurs in the As layer, while the oxidation of the outer edge of the low-aluminum layer is limited to a small section outside the defect isolation area, thus effectively reducing the stress generated. Step 10: Deposit a dielectric protective layer on the epitaxial wafer obtained in Step 9. The thickness of the dielectric protective layer is 50-500 nm, and the material is SiO2, Al2O3, TiO2, or SiN. xThe epitaxial films are made of single-layer or multi-layer composite materials such as SiON, and the coating process is PECVD or ALD. See the attached image for the resulting epitaxial wafers. Figure 13 ; Step 11: Coat the surface of the epitaxial wafer obtained in Step 10 with photoresist, the photoresist film thickness is 1-5 μm; expose and develop the photoresist until only the metal vias on the dielectric protective layer are free of photoresist, and the remaining areas are covered by photoresist; etch away the dielectric film and remove the photoresist to form the metal vias, see [link to relevant documentation]. Figure 14 ; Step 12: Deposit metal onto the epitaxial wafer obtained in Step 11. The metal may be Au, Pt, Ag, Al, etc. (See [link to relevant documentation]). Figure 15 .

Claims

1. A vertical-cavity surface-emitting laser with a defect isolation region, comprising an active region platform, wherein the active region platform comprises, from bottom to top, a partially first DBR layer, an active layer, an oxide confinement layer, and a second DBR layer; characterized in that, A defect isolation region is provided in the second DBR layer. The defect isolation region includes a vertical trench near the edge of the active region platform and surrounding the central region of the active region platform. The vertical trench has a closed shape when projected in the horizontal direction. The vertical trench is filled with a high thermal conductivity ceramic material. The defect isolation region is formed before the formation of the oxide confinement layer.

2. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 1, characterized in that, Before filling the high thermal conductivity ceramic material, the inner wall of the vertical groove is surface treated with trimethylaluminum. The specific method is as follows: under a treatment temperature of 250-350 ℃ and a treatment pressure of 50-500 Pa, the following cycle treatment is performed several times: first, trimethylaluminum is introduced into the reaction chamber for 5-60 s, and then nitrogen is introduced for 5-60 s.

3. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 2, characterized in that, Prior to the trimethylaluminum surface treatment, the active zone platform with the vertical grooves undergoes heat treatment under nitrogen protection at a temperature of 250-350 °C for 30-60 min.

4. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 2, characterized in that, Before the trimethylaluminum surface treatment, the active region platform with the vertical grooves is subjected to hydrogen heat treatment. The specific method is as follows: the active region platform with the vertical grooves is heat treated in a hydrogen atmosphere at a temperature of 350-500℃ for a time of 15-30 min.

5. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 1, characterized in that, Before filling with the high thermal conductivity ceramic material, the active region platform with the vertical grooves is subjected to hydrogen heat treatment. The specific method is as follows: the active region platform with the vertical grooves is heat treated in a hydrogen atmosphere at a temperature of 350-500℃ for a time of 25-40 min.

6. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 1, characterized in that, The vertical trench has the same horizontal projection shape as the active area platform.

7. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 1, characterized in that, The vertical trench is 0.5 μm to 3 μm away from the edge of the active area platform in the horizontal direction.

8. The vertical-cavity surface-emitting laser with a defect isolation region as described in claim 1, characterized in that, The high thermal conductivity ceramic material is any one of the following materials: AlN, AlCrN, CrN, TiN, TiAlN, TaN, SiC.

Images