A high polarization semiconductor laser

Abstract

This application relates to the technical field of lasers, and more particularly to a high-polarization semiconductor laser, comprising, from bottom to top, an N-face electrode, a substrate, a buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper confinement layer, an ohmic contact layer, and a P-face electrode. A current injection region is provided on the ohmic contact layer, and several confinement regions are provided within the current injection region. The confinement regions are linearly distributed on both sides of the current injection region to form a confinement layer. Multiple confinement layers are provided on each side of the current injection region, with gaps between the confinement layers. Gaps are also provided between confinement regions within the same confinement layer to form a current injection window. The confinement regions in adjacent confinement layers are staggered. The several confinement regions within the current injection region can prevent current injection, thereby suppressing TM mode lasing. According to the formula TE% = TE / (TE + TM), weakening TM can correspondingly enhance the polarization degree of TE.

Description

Technical Field

[0001] This application relates to the field of laser technology, and in particular to a high polarization semiconductor laser. Background Technology

[0002] Semiconductor lasers, due to their advantages such as compact structure, long lifespan, high reliability, high electro-optical conversion efficiency, fast modulation rate, wide wavelength range, and ease of integration, are widely used in fields including industrial production, lidar, military defense, optical communication, optical information storage, and medical aesthetics. With societal development and progress, higher requirements are being placed on the polarization degree of semiconductor lasers in many application areas. For example, in the industrial application of kilowatt to megawatt-level fiber lasers, 915 / 976nm semiconductor lasers used for optical pumping typically require a polarization degree of over 90% (TE). TE polarization degree is defined as TE% = TE / (TE + TM). Currently, through optimized design such as epitaxial structure, surface mount wire bonding packaging parameters, heat sink solder composition and thickness, and stack-up structure, the TE polarization degree of 915 / 976 semiconductor laser chips can typically reach around 95%, but it is difficult to further improve it to a higher level.

[0003] Based on the above background, this invention proposes a novel semiconductor laser chip design to achieve higher TE polarization. Summary of the Invention

[0004] To achieve higher TE polarization, this application provides a high polarization semiconductor laser.

[0005] The high polarization semiconductor laser provided in this application adopts the following technical solution:

[0006] A high-polarization semiconductor laser includes, from bottom to top, an N-face electrode, a substrate, a buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper confinement layer, an ohmic contact layer, and a P-face electrode. The ohmic contact layer has a current injection region, which includes a horizontal plane facing the P-face electrode. The horizontal plane includes two long sides and two short sides. A plurality of confinement layers symmetrically distributed along the two long sides are provided within the horizontal plane. The confinement layers are parallel to the long sides and are composed of several confinement regions arranged sequentially along the long side. Gaps are left between confinement regions within the same confinement layer to form current injection windows. The confinement regions in adjacent confinement layers are staggered. Multiple confinement layers are provided alongside each long side, with gaps between the confinement layers.

[0007] Actual near-field testing of semiconductor laser chips revealed that the main region of TM mode lasing is distributed on both sides of the current injection region. By employing the aforementioned technical solution, several confinement regions within the current injection region can prevent current injection, thereby suppressing TM mode lasing. Furthermore, according to the formula TE% = TE / (TE + TM), weakening TM corresponds to enhancing the polarization degree of TE.

[0008] Preferably, the projection of the restricted area onto the horizontal plane is square, and the projection of the restricted area onto the horizontal plane includes a wide side parallel to the long side and a high side parallel to the short side. The length L1 of the wide side is 5-500 μm, the length H2 of the high side is 5-50 μm, the horizontal distance S1 between adjacent restricted areas within the same restricted layer is 5-100 μm, the distance S2 between adjacent restricted layers is 5-100 μm, the minimum distance d1 between the restricted area closest to the short side and the short side is 5-200 μm, and the minimum distance d2 between the restricted layer closest to the long side and the long side is 5-200 μm.

[0009] Preferably, the length of the short side is H1, and the distance between the top of the outermost limiting layer and the bottom of the innermost limiting layer on a single long side is H3, wherein the ratio of H3 to H1 is between 1:10 and 1:3.

[0010] By adopting the above technical solution, the restriction areas are staggered, and the gaps between the restriction areas are open to current flow, thereby suppressing the TM mode while reducing the impact on the TE mode.

[0011] Preferably, an insulating layer is provided between the P-side electrode and the ohmic contact layer, the insulating layer including a plurality of insulating blocks for forming a restricted area.

[0012] By adopting the above technical solution, the current is transmitted downward through the ohmic contact layer, while the insulating layer can prevent current injection in this area, thereby suppressing the TM mode.

[0013] Preferably, the ohmic contact layer is etched with a plurality of grooves, the bottom of the grooves being an upper confinement layer, the doping concentration of the upper confinement layer being lower than the doping concentration of the ohmic contact layer, and the grooves constituting a confinement region.

[0014] By adopting the above technical solution, the P-side electrode at the groove contacts the upper confinement layer. The lower doping concentration at this location results in poor ohmic contact between the electrode and the P-side electrode above, leading to a higher series resistance between them. This reduces current injection and suppresses the TM mode.

[0015] Preferably, the groove is provided with an insulating layer.

[0016] By adopting the above technical solution, the insulating layer improves the current restriction effect in this area, thereby further improving the suppression effect on TM mode.

[0017] Preferably, the doping concentration of the ohmic contact layer is 2E19-1E20 cm⁻¹. -3 The thickness is 200nm-800nm, and the doping concentration of the upper confinement layer is 5E17-1E19cm. -3 .

[0018] By adopting the above technical solution, the doping concentration of the ohmic contact layer is limited so that the P-side electrode can form a good ohmic contact with the ohmic contact layer.

[0019] Preferably, the insulating layer is made of one of SiO2, Si3N4 or a composite film thereof.

[0020] In summary, this application includes at least one of the following beneficial technical effects:

[0021] By setting the confinement region, the TM mode gain of the current injection region can be suppressed, thereby improving the TE polarization degree of the semiconductor laser;

[0022] The process for suppressing TM mode lasing is compatible with existing processes, can share mask and preparation processes, and does not require the introduction of additional processes, thus reducing manufacturing costs. Attached Figure Description

[0023] Figure 1 This is a lasing pattern of an existing semiconductor laser chip in TM mode;

[0024] Figure 2 This is a schematic diagram of the structure of the high polarization semiconductor laser in the embodiment;

[0025] Figure 3 This is a schematic diagram of the current injection region in the embodiment;

[0026] Figure 4 This is a schematic diagram of the restricted area in Embodiment 1;

[0027] Figure 5 This is a schematic diagram of the structure of the restricted area in Embodiment 2;

[0028] Figure 6 This is a schematic diagram of the restricted area in Embodiment 3.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1. N-side electrode; 2. Substrate; 3. Buffer layer; 4. Lower confinement layer; 5. Lower waveguide layer; 6. Quantum well active layer; 7. Upper waveguide layer; 8. Upper confinement layer; 9. Ohmic contact layer; 10. P-side electrode; 11. Current injection region; 12. Confinement region; 13. Current injection window; 14. Insulating layer; 15. Insulating block; 16. Groove. Detailed Implementation

[0031] The present application will be further described in detail below with reference to all the accompanying drawings.

[0032] like Figure 1 Through actual near-field testing of existing semiconductor laser chips, operators discovered that the main region of TM mode lasing is distributed on both sides of the current injection region 11. To improve TE polarization, it is necessary to suppress TM mode lasing on both sides of the current injection region 11. Based on this, this application designs a high-polarization semiconductor laser.

[0033] This application discloses a high-polarization semiconductor laser, referring to... Figures 2 to 3 It includes, from bottom to top, an N-side electrode 1, a substrate 2, a buffer layer 3, a lower confinement layer 4, a lower waveguide layer 5, a quantum well active layer 6, an upper waveguide layer 7, an upper confinement layer 8, an ohmic contact layer 9, and a P-side electrode 10.

[0034] Reference Figures 2 to 3 The ohmic contact layer 9 has a current injection region 11, which includes a horizontal plane facing the P-side electrode 10. The horizontal plane includes two long sides and two short sides. Several confinement layers symmetrically distributed along the two long sides are provided within the horizontal plane. The confinement layers are parallel to the long sides and consist of several confinement regions 12. The confinement regions 12 within the same confinement layer are arranged sequentially along the long side. The confinement layers suppress the current on both sides of the current injection region 11, thereby effectively suppressing the TM mode on both sides of the current injection region 11.

[0035] Reference Figures 2 to 3 Each long side has multiple confinement layers. In this embodiment, the current injection region 11 has three confinement layers on each side. Of course, it doesn't have to be three layers, as long as the following proportional relationship is met; here, we are only illustrating with three layers. Gaps are left between the confinement layers to allow current to pass through. The length of the short side is H1, and the sum of the lengths of all confinement layers along a single long side is H3, where the ratio of H3 to H1 is between 1:10 and 1:3. Here, H3 refers to the distance between the top of the outermost confinement layer and the bottom of the innermost confinement layer. The overall ratio of H3 to H1 is determined based on the distribution of TM mode lasing throughout the current injection region 11.

[0036] Reference Figures 2 to 3The projection of the restriction area 12 onto the horizontal plane is square, and the projection of the restriction area 12 onto the horizontal plane includes a wide side parallel to the long side and a high side parallel to the short side. The length L1 of the wide side is 5-500μm, the length H2 of the high side is 5-50μm, the horizontal distance S1 between adjacent restriction areas 12 within the same restriction layer is 5-100μm, the distance S2 between adjacent restriction layers is 5-100μm, the minimum distance d1 between the restriction area 12 closest to the short side and the short side is 5-200μm, and the minimum distance d2 between the restriction layer closest to the long side and the long side is 5-200μm.

[0037] Reference Figures 2 to 3 Within the same confinement layer, a gap is left between confinement regions 12 to form a current injection window 13, and the confinement regions 12 in adjacent confinement layers are staggered. The current injection window 13 between confinement regions 12 and the gap between confinement layers serve the same purpose: to facilitate current flow. The confinement region 12 can suppress the TM mode, while the current injection window 13 and the gap between confinement layers ensure the lasing of the TE mode on both sides of the current injection region 11.

[0038] The implementation principle of a high-polarization semiconductor laser according to an embodiment of this application is as follows: current is introduced from the P-side electrode 10 and finally extracted from the N-side electrode 1. When the current passes through the ohmic contact layer 9, the conductivity at the direct contact between the P-side electrode 10 and the ohmic contact layer 9 is good, and the current can pass smoothly. The confinement region 12 can restrict the current passing through this region, thereby achieving a current suppression effect, and thus suppressing the TM mode on both sides of the current injection region 11, thereby improving the TE polarization degree.

[0039] Example 1

[0040] Reference Figure 4 In this embodiment, the restricted region 12 is composed of an insulating layer 14, which is made of one of SiO2, Si3N4, or a composite film thereof, with a thickness between 100-300 nm. The insulating layer 14 is located between the P-side electrode 10 and the ohmic contact layer 9, and includes insulating blocks 15 distributed on both sides of the current injection region 11 to form the restricted region 12. Part of the P-side electrode 10 is in direct contact with the ohmic contact layer 9, and another part is in contact with the insulating blocks 15. The insulating blocks 15 block the current passing through this region, thereby limiting the current.

[0041] Example 2

[0042] Reference Figure 5In this embodiment, the restricted region 12 differs from that in Embodiment 1: several grooves 16 are etched on the ohmic contact layer 9, and the highly doped portion of the upper restricted layer 8 is etched away. The bottom of the grooves 16 is located in the low-doped region of the upper restricted layer 8. The grooves 16 constitute the restricted region 12. Furthermore, the doping concentration of the upper restricted layer 8 is lower than that of the ohmic contact layer 9. The doping concentration of the ohmic contact layer 9 is 2E19-1E20 cm⁻¹. -3 The thickness is 200nm-800nm, and the doping concentration of the upper confinement layer 8 is 5E17-1E19cm. -3 The P-side electrode 10 at the groove 16 contacts the upper confinement layer 8. The lower doping concentration at this location results in poor ohmic contact between the electrode and the P-side electrode 10 above it, leading to a higher series resistance between them. This reduces current injection and suppresses the TM mode.

[0043] Example 3

[0044] The difference between Example 3 and Example 2 is as follows: (Refer to...) Figure 6 An insulating layer 14 is provided within the groove 16. The insulating layer 14 is made of one of SiO2, Si3N4, or a composite film thereof, with a thickness between 100-300 nm. The insulating layer 14 can better limit the current within the groove 16, thereby improving the suppression effect on TM mode.

[0045] 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 high-polarization semiconductor laser, comprising, from bottom to top, an N-plane electrode (1), a substrate (2), a buffer layer (3), a lower confinement layer (4), a lower waveguide layer (5), a quantum well active layer (6), an upper waveguide layer (7), an upper confinement layer (8), an ohmic contact layer (9), and a P-plane electrode (10), characterized in that: The ohmic contact layer (9) is provided with a current injection region (11). The current injection region (11) includes a horizontal plane facing the P-side electrode (10). The horizontal plane includes two long sides and two short sides. Several confinement layers are symmetrically distributed on the two long sides within the horizontal plane. The confinement layers are parallel to the long sides. The confinement layers are composed of several confinement areas (12). The confinement areas (12) are arranged sequentially along the long side. A gap is left between the confinement areas (12) in the same confinement layer to form a current injection window (13). The confinement areas (12) in two adjacent confinement layers are staggered. Multiple confinement layers are provided next to each long side, and a gap is left between the confinement layers.

2. A high polarization semiconductor laser according to claim 1, characterized in that: The projection of the restricted area (12) on the horizontal plane is square, and the projection of the restricted area on the horizontal plane includes a wide side parallel to the long side and a high side parallel to the short side. The length of the wide side L1 is 5-500μm, the length of the high side H2 is 5-50μm, the horizontal distance S1 between adjacent restricted areas (12) in the same restricted layer is 5-100μm, the distance S2 between adjacent restricted layers is 5-100μm, the minimum distance d1 between the restricted area (12) closest to the short side and the short side is 5-200μm, and the minimum distance d2 between the restricted layer closest to the long side and the long side is 5-200μm.

3. A high-polarization semiconductor laser according to claim 1, characterized in that: The length of the short side is H1, and the distance between the top of the outermost limiting layer and the bottom of the innermost limiting layer on a single long side is H3, wherein the ratio of H3 to H1 is between 1:10 and 1:

3.

4. A high polarization semiconductor laser according to claim 1, characterized in that: An insulating layer (14) is provided between the P-side electrode (10) and the ohmic contact layer (9), the insulating layer (14) including a plurality of insulating blocks (15) for forming the restricted area (12).

5. A high polarization semiconductor laser according to claim 1, characterized in that: The ohmic contact layer (9) has several grooves (16) etched on it. The bottom of the grooves (16) is an upper confinement layer (8). The doping concentration of the upper confinement layer (8) is lower than that of the ohmic contact layer (9). The grooves (16) constitute a confinement region (12).

6. A high-polarization semiconductor laser according to claim 5, characterized in that: An insulating layer (14) is provided inside the groove (16).

7. A high-polarization semiconductor laser according to claim 5, characterized in that: The doping concentration of the ohmic contact layer (9) is 2E19-1E20 cm⁻¹ -3 The thickness is 200nm-800nm, and the doping concentration of the upper confinement layer (8) is 5E17-1E19cm. -3 .

8. A high-polarization semiconductor laser according to claim 4 or 6, characterized in that: The insulating layer (14) is made of one of SiO2, Si3N4 or a composite film thereof.

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