Single-mode surface-emitting laser and its fabrication method

Abstract

This invention discloses a single-mode surface-emitting laser and its fabrication method. The single-mode surface-emitting laser includes a substrate, an N-type diode-emitter (DBR), an active layer, a confinement layer, and a P-type DBR stacked sequentially. An N-type electrode is disposed on the substrate, and a P-type electrode and an emission port are disposed on the P-type DBR. The confinement layer includes a central emission port and an oxide region surrounding it. The active layer includes a central resonant region and a surrounding grating region. A complex number of concentric annular gratings surround the resonant region on the grating region, with the diameter of the innermost annular grating being greater than or equal to the diameter of the emission port. This invention maintains a constant active layer thickness, reduces the emission area of ​​the resonant region, avoids device collapse and breakage, and keeps other parts of the device structure unaffected. It easily achieves single-mode, low-threshold-current operation, promoting high-speed data transmission and optical communication applications.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more particularly to a single-mode surface-emitting laser and its manufacturing method. Background Technology

[0002] Current vertical-angle lasers (VCSELs) do not perform ideally in single-mode operation. To achieve single-longitudinal-mode operation and a low current threshold in VCSELs, the common approach is to improve the active region structure or reduce the oxide aperture. Improving the active region structure typically involves reducing the number of active region layers or, while maintaining the same number of layers, decreasing the active region thickness to obtain a smaller VCSEL with a shorter cavity length. However, this approach is not ideal because laser gain decreases as the active region thickness decreases. Reducing the oxide aperture can lower the threshold current, but it increases the manufacturing difficulty of the VCSEL, leading to higher operating temperatures and more severe heat generation, thus affecting device reliability and significantly limiting the lifespan of high-speed data transmission and optical communication. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a single-mode surface-emitting laser and its manufacturing method.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A single-mode surface-emitting laser includes a substrate, an N-type diode-guided laser (DBR), an active layer, a confinement layer, and a P-type DBR stacked sequentially. The substrate has an N-type electrode, and the P-type DBR has a P-type electrode and an emission port. The confinement layer includes an emission port in the center and an oxide region around it. The active layer includes a resonant region in the center and a grating region around it. The grating region has a plurality of concentric annular gratings surrounding the resonant region, and the diameter of the innermost annular grating is greater than or equal to the diameter of the emission port.

[0006] Preferably, the diameter of the innermost annular grating is 0-100 nm larger than the diameter of the light-emitting aperture.

[0007] Preferably, from the inside out, the odd-numbered annular gratings are grooves and the even-numbered annular gratings are protrusions, or the odd-numbered annular gratings are protrusions and the even-numbered annular gratings are grooves, and the grooves are filled with P-type DBR material.

[0008] Preferably, the depth of the groove and the thickness of the protrusion are 0-4 nm smaller than the thickness of the active layer.

[0009] Preferably, from the inside out, the odd-numbered annular gratings are modified structures and the even-numbered annular gratings are unmodified structures, or the odd-numbered annular gratings are unmodified structures and the even-numbered annular gratings are modified structures.

[0010] Preferably, the thickness of the modified structure is 0-4 nm smaller than the thickness of the active layer.

[0011] Preferably, the resonant region is a three-layer InGaAs layer, and the doping concentration of In in the middle InGaAs layer is different from that of the two layers above and below it.

[0012] Preferably, the width of the grating region is 8 μm, and the period of the annular grating within the grating region is 40.

[0013] Preferably, the difference between the outer and inner radii of each annular grating is 100 nm.

[0014] A method for fabricating a single-mode surface-emitting laser includes the following steps:

[0015] 1) Provide an intermediate process structure for a surface-emitting laser, the intermediate process structure including a substrate and an N-type DBR and an active layer above the substrate;

[0016] 2) A photoresist layer is coated on the active layer, the photoresist layer is irradiated with an electron beam and the electron beam is moved, and then a plurality of concentrically spaced annular opening windows are formed on a preset grating area by development.

[0017] 3) The active layer within the annular opening window is etched or modified, and the remaining photoresist layer is stripped to form the central resonant region and the surrounding grating region. The grating region is provided with a plurality of concentric annular gratings surrounding the resonant region.

[0018] 4) A P-type DBR is epitaxially grown above the active layer, and a confinement layer is formed by oxidation of the P-type DBR. The confinement layer includes a light-emitting aperture in the middle and an oxidized region around it. The diameter of the light-emitting aperture is less than or equal to the diameter of the innermost annular grating.

[0019] 5) A P-type electrode and a light-emitting port are formed on the P-type DBR, and an N-type electrode is formed on the substrate. Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The single-mode surface-emitting laser of the present invention can generate a single-mode laser by changing the structure of the active layer and providing a grating region and a resonator on the active layer, thereby enhancing the singleness of light output.

[0021] (2) The single-mode surface-emitting laser of the present invention reduces the size of the resonant region in the active layer, changes the active layer structure and refractive index, and improves the electro-optic conversion efficiency.

[0022] (3) The present invention can keep the thickness of the active layer of the device unchanged, reduce the volume of the resonant region, avoid device collapse and breakage, keep other structures of the device unaffected, easily realize single longitudinal mode and low threshold current operation, and promote high-speed data transmission and optical communication applications. Attached Figure Description

[0023] Figure 1 This is a cross-sectional schematic diagram of a single-mode surface-emitting laser according to an embodiment of the present invention;

[0024] Figure 2 This is a top cross-sectional view of the active layer of a single-mode surface-emitting laser according to an embodiment of the present invention;

[0025] Figures 3a-3c This is a schematic flowchart illustrating a method for fabricating a single-mode surface-emitting laser according to an embodiment of the present invention.

[0026] Figure reference numerals: 1. Substrate; 2. N-type DBR; 3. Active layer; 31. Resonant region; 32. Grating region; 33. Ring grating; 4. Confinement layer; 41. Light exit aperture; 42. Oxidation region; 5. P-type DBR; 6. N-type electrode; 7. P-type electrode; 8. Passivation layer. Detailed Implementation

[0027] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are merely illustrative to facilitate understanding of the invention, and their specific proportions can be adjusted according to design requirements. The vertical relationships of relative elements and the definitions of front / back in the graphics described herein should be understood by those skilled in the art to refer to the relative positions of the components; therefore, they can all be flipped to present the same component, and all of this should fall within the scope disclosed in this specification.

[0028] refer to Figure 1 This application discloses a single-mode surface-emitting laser, comprising a substrate 1, an N-type DBR 2, an active layer 3, a confinement layer 4, and a P-type DBR 5 stacked sequentially. An N-type electrode 6 is disposed on the substrate 1 surrounding the N-type DBR 2. A P-type electrode 7 and an emission port are disposed on the top of the P-type DBR 5. The confinement layer 4 includes an emission port 41 in the center and an oxide region 42 around it. The active layer 3 includes a resonant region 31 and a grating region 32. The resonant region 31 is located in the center, and the grating region 32 is located around the resonant region 31. Light is emitted from the resonant region 31, exits through the emission port 41, is reflected by the N-type DBR 2 and the P-type DBR 5, and exits from the emission port on top of the P-type DBR 5. (Reference) Figure 2The grating region 32 is provided with a plurality of concentric annular gratings 33 surrounding the resonant region 31. The annular gratings 33 reflect the light emitted from the resonant region 31, allowing as much light as possible to exit through the light exit aperture 41. This effectively improves the single-mode output of the active layer 3, achieving single-mode output and ensuring structural stability. Furthermore, the diameter of the innermost annular grating 33 is greater than or equal to the diameter of the light exit aperture 41, thus allowing as much light as possible to pass through the light exit aperture 41 and exit from the top light exit port, increasing the intensity of the single-mode output light. Specifically, the diameter of the innermost annular grating 33 is 0-100 nm larger than the diameter of the light exit aperture 41. Within this range, single-longitudinal-mode, low threshold current operation of the device can be achieved.

[0029] In one embodiment, from the inside out, the odd-numbered annular gratings 33 are grooves and the even-numbered annular gratings 33 are protrusions, or the odd-numbered annular gratings 33 are protrusions and the even-numbered annular gratings 33 are grooves, and the grooves are filled with P-type DBR material. The grooves separate adjacent protrusions, disrupting the original complete structure of the active layer 3, so that light is emitted only in the resonant region 31, while the grating region 32 cannot emit light normally, achieving single-mode light emission, enhancing the singleness of light, and reducing the light emission area of ​​the active layer 3, changing the structure and refractive index of the active layer 3, and improving the electro-optical conversion efficiency. The protrusions can play a structural support role, preventing the device from collapsing or breaking. Specifically, the depth of the groove and the thickness of the protrusion are 0-4 nm smaller than the thickness of the active layer. That is, the bottom of the groove may not penetrate the entire active layer 3, retaining part of the structure of the lowest layer of the active layer 3. Furthermore, the projection width of the protrusion on the substrate 1 can be greater than or equal to the projection width of the groove on the substrate 1, to further improve the support strength of the protrusion.

[0030] In another embodiment, from the inside out, the odd-numbered annular gratings 33 are modified structures, and the even-numbered annular gratings 33 are unmodified structures, or the odd-numbered annular gratings 33 are unmodified structures and the even-numbered annular gratings 33 are modified structures. Specifically, the resonant region 31 is a three-layer InGaAs layer, and the doping concentration of In in the middle InGaAs layer is different from the doping concentration of In in the layers above and below it. In this embodiment, the material of the grating region 32 on the active layer 3 can be modified so that the grating region 32 cannot emit light normally, and only the resonant region 31 can emit light normally. Specifically, the material properties of a part of the grating region 32 are changed, the original InGaAs material is modified to obtain a modified structure, which destroys the structure of the active layer 3 and reduces the light transmission area of ​​the active layer 3. Although some unmodified structures are retained in the grating region 32, the two adjacent unmodified structures are separated by the modified structure and cannot emit light normally, thus realizing the single-mode light output of the middle resonant region 31. Specifically, the thickness of the modified structure is 0-4 nm smaller than that of the active layer. Therefore, while keeping the thickness of the active layer 3 constant, the volume of the resonant region 31 can be reduced, thereby improving the single-mode optical output of the device.

[0031] Specifically, the substrate 1 is made of GaAs, and both the P-type DBR 5 and N-type DBR 2 are composed of AlGaAs and GaAs. The P-type DBR 5 and N-type DBR 2 are composed of several stacked reflective layers. In one embodiment, the total number of reflective layers in the P-type DBR 5 is 28 pairs, and the total number of reflective layers in the N-type DBR 2 is 33 pairs. The diameter of the P-type DBR 5 is 24 μm, the diameter of the resonant region 31 is 8 μm, and the width of the grating regions 32 on both sides is 8 μm. Within the grating region 32, the annular grating 33 and the resonant region 31 form a concentric ring structure. The difference between the outer ring radius and the inner ring radius of each annular grating 33 is 100 nm, the period length is 200 nm, the duty cycle is 50%, the period of the annular grating 33 is 8 μm / 200 nm = 40, the number of rings is 8 μm / 100 nm = 80, and the thickness of the annular grating 33 is 20 nm. Specifically, if the annular grating is a groove, then the depth of the groove is 20nm.

[0032] In a specific embodiment, a passivation layer 8 is also included, which covers the area on the surface of the substrate 1 other than the N-type electrode 6, and extends from both sides of the N-type DBR 2 to the top of the P-type DBR 5 other than the P-type electrode 7 and the light outlet.

[0033] Correspondingly, reference Figures 3a-3c and Figure 1 The embodiments of this application also propose a method for fabricating a single-mode surface-emitting laser, comprising the following steps:

[0034] (1)Reference Figure 3aAn intermediate fabrication structure for a surface-emitting laser is provided. This intermediate fabrication structure includes a substrate 1, an N-type digital laser receiver (DBR) 2, and an active layer 3 above the substrate 1. The N-type DBR 2 is composed of several stacked reflective layers, and the active layer 3 is composed of at least three stacked quantum well structures. Preferably, the substrate 1 is GaAs, the active layer 3 is a three-layer quantum well structure, the N-type DBR 2 is composed of AlGaAs and GaAs, and the active layer 3 is made of InGaAs. The N-type DBR 2 and the active layer 3 are epitaxially grown on the substrate 1 in a single step, and growth is stopped when the three-layer quantum well structure is reached.

[0035] (2) A photoresist layer is coated on top of the active layer 3. The photoresist layer is irradiated with an electron beam. The electron beam is moved, and development is performed to form multiple concentrically spaced annular development windows on a preset grating area, defining the shape of the annular grating 33. Using electron beam exposure can ensure good shape consistency of the obtained annular grating 33. Specifically, a positive photoresist layer is formed by covering the active layer 3. The photoresist layer irradiated by the electron beam will be denatured. After immersing its surface in the developing solution, annular development windows will appear in the part irradiated by the electron beam, realizing grating replication.

[0036] (3)Reference Figure 3b The active layer 3 within the annular visible window is etched or modified, and the remaining photoresist layer is stripped off to form a grating region 32 and a resonant region 31. The resonant region 31 is used for light emission. A plurality of concentric annular gratings 33 are provided on the grating region 32 surrounding the resonant region 31. The annular gratings 33 reflect the light from the resonant region 31, allowing as much light as possible to converge and exit from the resonant region 31, effectively improving the single-mode emission of the active layer 3, achieving single-mode light emission, and ensuring structural stability. In one embodiment, the active layer 3 within the annular visible window is dry-etched in the grating region 32 to form a groove, and the remaining unetched portion forms a protrusion. In another embodiment, the active layer 3 within the annular visible window is modified in the grating region 32. The modification method can be ion implantation, etc., to disrupt the material properties of the active layer 3. The modified portion forms a modified structure, and the remaining portion forms an unmodified structure.

[0037] (4)Reference Figure 3cA P-type DBR 5 is epitaxially grown above the active layer 3, and a confinement layer 4 is formed by oxidation of the P-type DBR 5. The confinement layer 4 includes a central light-emitting aperture 41 and an outer oxide region 42. The light-emitting aperture 41 is positioned opposite to the resonant region 31, ensuring that the light emitted from the resonant region 31 exits through the light-emitting aperture 41. Specifically, the P-type DBR 5 is composed of AlGaAs and GaAs. After the P-type DBR 5 is epitaxially grown, an oxide region 42 is formed on the outer periphery of the P-type DBR 5 from the side, and a light-emitting aperture 41 is formed in the middle. Specifically, the diameter of the light-emitting aperture 41 is less than or equal to the diameter of the innermost annular grating 33. The diameter of the light-emitting aperture 41 is 0-100 nm smaller than the diameter of the innermost annular grating 33, thus allowing as much light emitted from the resonant region 31 as possible to pass through the light-emitting aperture 41 and exit through the light-emitting port, thereby increasing the intensity of the single-mode output light. During device operation, current can flow from the light-emitting aperture 41 to the resonant region 31, where single-mode light output is achieved. If the annular grating 33 is a groove, then during the secondary epitaxial growth of the P-type DBR 5, the groove is filled with P-type DBR 5 material, i.e., AlGaAs or GaAs, to keep the upper surface of the active layer 3 flat, thereby further ensuring the growth quality of the P-type DBR 5.

[0038] (5)Reference Figure 1 A P-type electrode 7 and a light outlet are fabricated on a P-type DBR 5, and an N-type electrode 6 is fabricated on a substrate 1. The P-type electrode 7 and the light outlet are located on the top of the P-type DBR 5, and the N-type electrode 6 is located on the substrate 1 surrounding the N-type DBR 2.

[0039] (6) A passivation layer 8 is deposited, which covers the area on the surface of the substrate 1 except for the N-type electrode 6, and extends from both sides of the N-type DBR2 to the top of the P-type DBR 5 except for the P-type electrode 7 and the light outlet. Therefore, while ensuring that single-mode light can be emitted from the light outlet, the stability of the device can also be improved.

[0040] The above embodiments are only used to further illustrate the technical solution of the present invention, but the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A single-mode surface-emitting laser, characterized in that: The device comprises a substrate, an N-type DBR, an active layer, a confinement layer, and a P-type DBR stacked sequentially. The substrate has an N-type electrode, and the P-type DBR has a P-type electrode and a light-emitting port. The confinement layer includes a central light-emitting port and an oxide region surrounding it. The active layer includes a central resonant region and a surrounding grating region. The grating region has a plurality of concentric annular gratings surrounding the resonant region, with the innermost annular grating having a diameter greater than or equal to the diameter of the light-emitting port. From the inside out, odd-numbered annular gratings are modified structures, and even-numbered annular gratings are unmodified structures, or vice versa.

2. The single-mode surface-emitting laser according to claim 1, characterized in that: The diameter of the innermost annular grating is 0-100 nm larger than the diameter of the light-emitting aperture.

3. The single-mode surface-emitting laser according to claim 1, characterized in that: From the inside out, the odd-numbered annular gratings are grooves and the even-numbered annular gratings are protrusions, or the odd-numbered annular gratings are protrusions and the even-numbered annular gratings are grooves, and the grooves are filled with P-type DBR material.

4. The single-mode surface-emitting laser according to claim 3, characterized in that: The depth of the groove and the thickness of the protrusion are 0-4 nm less than the thickness of the active layer.

5. The single-mode surface-emitting laser according to claim 1, characterized in that: The thickness of the modified structure is 0-4 nm less than the thickness of the active layer.

6. The single-mode surface-emitting laser according to claim 1, characterized in that: The resonant region consists of three InGaAs layers, and the doping concentration of In in the middle InGaAs layer is different from that of the two In layers above and below it.

7. The single-mode surface-emitting laser according to claim 1, characterized in that: The width of the grating region is 8 μm, and the period of the annular grating within the grating region is 40.

8. The single-mode surface-emitting laser according to claim 1, characterized in that: The difference between the outer and inner radii of each of the aforementioned annular gratings is 100 nm.

9. A method for fabricating a single-mode surface-emitting laser based on any one of claims 1-8, characterized in that: Includes the following steps: 1) Provide an intermediate process structure for a surface-emitting laser, the intermediate process structure including a substrate and an N-type DBR and an active layer above the substrate; 2) A photoresist layer is coated on the active layer, the photoresist layer is irradiated with an electron beam and the electron beam is moved, and then a plurality of concentrically spaced annular opening windows are formed on the preset grating area by development. 3) The active layer within the annular opening window is etched or modified, and the remaining photoresist layer is stripped to form the central resonant region and the surrounding grating region. The grating region is provided with a plurality of concentric annular gratings surrounding the resonant region. 4) A P-type DBR is epitaxially grown above the active layer, and a confinement layer is formed by oxidation of the P-type DBR. The confinement layer includes a light-emitting aperture in the middle and an oxidized region around it. The diameter of the light-emitting aperture is less than or equal to the diameter of the innermost annular grating. 5) A P-type electrode and a light outlet are formed on the P-type DBR, and an N-type electrode is formed on the substrate.

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