Semiconductor laser with high polarization degree

Abstract

The invention relates to the technical field of lasers, in particular to a high-polarization-degree semiconductor laser which comprises an N-face electrode, a substrate, a buffer layer, a lower limiting layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper limiting layer, an ohmic contact layer and a P-face electrode which are sequentially arranged from bottom to top. A plurality of limiting areas are arranged in the current injection area, the limiting areas are linearly distributed on the two sides of the current injection area to form limiting layers, multiple limiting layers are arranged on each side of the current injection area, gaps are reserved between the limiting layers, and gaps are reserved between the limiting areas in the same limiting layer to form current injection windows. The limiting areas in every two adjacent limiting layers are arranged in a staggered mode. And a plurality of limiting regions are arranged in the current injection region, so that the injection of the current can be prevented, and the lasing of a TM mode can be inhibited. And according to the formula of TE% = TE / (TE + TM), the TE polarization degree can be correspondingly enhanced after TM is weakened.

Description

Technical Field

[0001] The present application relates to the technical field of lasers, and in particular to a semiconductor laser with high polarization degree. Background Art

[0002] Semiconductor lasers are widely used in fields including industrial production, laser radar, military attack and defense, optical communications, optical information storage and medical cosmetology due to their compact structure, long life, high reliability, high electro-optical conversion efficiency, fast modulation rate, wide wavelength range and easy integration. With the development and progress of society, higher requirements are placed on the polarization degree of semiconductor lasers in many application fields. For example, in the industrial application of kilowatt to 10,000-watt fiber lasers, the 915 / 976nm semiconductor lasers used for optical pumping are usually required to have a TE polarization degree of more than 90%, and the TE polarization degree is defined as TE%=TE / (TE+TM). At present, through the optimization of epitaxial structure, patch wire bonding packaging parameters, heat sink solder component thickness and stacking structure, the TE polarization degree of 915 / 976 semiconductor laser chips can usually reach about 95%, but it is difficult to further increase it to a higher level.

[0003] Based on the above background, the present invention advocates a new semiconductor laser chip design to achieve higher TE polarization degree. Summary of the invention

[0004] In order to achieve a higher TE polarization degree, the present application provides a semiconductor laser with a high polarization degree.

[0005] A high polarization semiconductor laser provided in this application adopts the following technical solution: A semiconductor laser with high polarization degree comprises an N-face electrode, a substrate, a buffer layer, a lower limiting layer, a lower waveguide layer, a quantum well active layer, an upper waveguide layer, an upper limiting layer, an ohmic contact layer and a P-face electrode which are sequentially arranged from bottom to top, wherein a current injection region is arranged on the ohmic contact layer, a plurality of limiting regions are arranged in the current injection region, the limiting regions are symmetrically distributed on both sides of the current injection region, the limiting regions are linearly distributed on both sides of the current injection region to form limiting layers, multiple limiting layers are arranged on each side of the current injection region, gaps are left between limiting layers, gaps are left between limiting regions in the same limiting layer to form current injection windows, and limiting regions in two adjacent limiting layers are arranged alternately.

[0006] Through actual testing of the near field of semiconductor laser chips, it is found that the main areas of TM mode lasing are distributed on both sides of the current injection area. By adopting the above technical solution, several restriction areas set in the current injection area can prevent the injection of current, thereby suppressing the TM mode lasing. According to the formula TE%=TE / (TE+TM), the weakening of TM can correspondingly enhance the TE polarization degree.

[0007] Preferably, the restriction zone is arranged in a square shape, the width L1 of the restriction zone is 5-500μm, the height H2 is 5-50μm, the horizontal spacing S1 between adjacent restriction zones in the same restriction layer is 5-100μm, the spacing S2 between adjacent restriction layers is 5-100μm, the minimum distance d1 between the restriction zone at the end of the current injection zone and the end of the current injection zone is 5-200μm, and the minimum distance d2 between the restriction layer on the side of the current injection zone and the side of the current injection zone is 5-200μm.

[0008] Preferably, the height of the current injection region is H1, and the sum of the heights of all the confinement layers on one side of the current injection region is H3, wherein the ratio of H3 to H1 is between 1:10 and 1:3.

[0009] By adopting the above technical solution, the restriction areas are staggered and the gaps between the restriction areas are available for current to flow, thereby suppressing the TM mode and reducing the impact on the TE mode.

[0010] Preferably, an insulating layer is provided between the P-surface electrode and the ohmic contact layer, and the insulating layer includes a plurality of insulating blocks for constituting a restricted area.

[0011] By adopting the above technical solution, the current is transmitted downward through the ohmic contact layer, and the insulating layer can prevent the current injection into this area, thereby suppressing the TM mode.

[0012] Preferably, a plurality of grooves are etched on the ohmic contact layer, the bottom of the grooves is an upper limiting layer, the doping concentration of the upper limiting layer is lower than the doping concentration of the ohmic contact layer, and the grooves constitute a limiting area.

[0013] By adopting the above technical solution, the P-side electrode at the groove contacts the upper confinement layer. The lower doping concentration here makes its ohmic contact with the P-side electrode above it poor, and a higher series resistance is generated between the two, thereby reducing the injection of current to suppress the TM mode.

[0014] Preferably, an insulating layer is provided in the groove.

[0015] By adopting the above technical solution, the insulating layer improves the limiting effect of the current in the region, thereby further improving the suppression effect of the TM mode.

[0016] Preferably, the doping concentration of the ohmic contact layer is 2E19-1E20cm -3 , with a thickness of 200nm-800nm, and the doping concentration of the upper confinement layer is 5E17-1E19cm -3 .

[0017] 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.

[0018] Preferably, the insulating layer is made of SiO2, Si3N4 or a composite film layer thereof.

[0019] In summary, the present application includes at least one of the following beneficial technical effects: By setting the restriction region, the restriction region can suppress the TM mode gain of the current injection region and improve the TE polarization degree of the semiconductor laser; The process of suppressing TM mode lasing is compatible with existing processes and can share the mask and preparation process without introducing additional processes, thus reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the lasing diagram of the TM mode of the existing semiconductor laser chip; Figure 2 is a schematic structural diagram of a semiconductor laser with high polarization degree in an embodiment; Figure 3 is a schematic structural diagram of a current injection region in an embodiment; Figure 4 is a schematic diagram of the structure of the restricted area in Example 1; Figure 5 is a schematic diagram of the structure of the restricted area in Example 2; Figure 6 It is a schematic diagram of the structure of the restricted area in the third embodiment.

[0021] Description of reference numerals: 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. Insulation layer; 15. Insulation block; 16. Groove. DETAILED DESCRIPTION

[0022] The present application is further described in detail below in conjunction with all the accompanying drawings.

[0023] like Figure 1Through actual testing of the near field of an existing semiconductor laser chip, the operator found that the main areas of TM mode lasing are distributed on both sides of the current injection region 11. In order to improve the TE polarization degree, it is necessary to suppress the TM mode lasing on both sides of the current injection region 11. Based on this, the present application designs a semiconductor laser with a high polarization degree.

[0024] The present application embodiment discloses a semiconductor laser with high polarization degree, referring to Figures 2 to 3 , including 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, which are arranged in sequence from bottom to top.

[0025] Reference Figures 2 to 3 A current injection region 11 is provided on the ohmic contact layer 9, and a plurality of restriction regions 12 are provided in the current injection region 11. The restriction regions 12 are symmetrically distributed on both sides of the current injection region 11, and the restriction regions 12 are linearly distributed on both sides of the current injection region 11 to form a restriction layer. The restriction layer suppresses 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.

[0026] Reference Figures 2 to 3 , multiple restriction layers are provided on each side of the current injection zone 11. In the present embodiment, three restriction layers are provided on each side of the current injection zone 11. Of course, it may not be three layers, as long as the following proportional relationship is satisfied. Here, only three layers are used for explanation. A gap is left between the restriction layers for current to pass through. The height of the current injection zone 11 is H1, and the sum of the heights of all restriction layers on one side of the current injection zone 11 is H3, wherein the ratio of H3 to H1 is between 1:10 and 1:3. Among them, H3 refers to the distance between the top of the outermost restriction layer and the bottom end of the innermost restriction layer. The overall ratio of H3 and H1 is determined according to the distribution of TM mode lasing in the entire current injection zone 11.

[0027] Reference Figures 2 to 3 The restriction zone 12 is arranged in a square shape, the width L1 of the restriction zone 12 is 5-500μm, the height H2 is 5-50μm, the horizontal spacing S1 between adjacent restriction zones 12 in the same restriction layer is 5-100μm, the spacing S2 between adjacent restriction layers is 5-100μm, the minimum distance d1 between the restriction zone 12 at the end of the current injection zone 11 and the end of the current injection zone 11 is 5-200μm, and the minimum distance d2 between the restriction layer on the side of the current injection zone 11 and the side of the current injection zone 11 is 5-200μm.

[0028] Reference Figures 2 to 3, a gap is left between the restriction areas 12 and the restriction areas 12 in the same restriction layer to form a current injection window 13, and the restriction areas 12 in two adjacent restriction layers are arranged alternately. The current injection windows 13 between the restriction areas 12 and the gaps between the restriction layers have the same function, which is to flow current. The restriction area 12 can suppress the TM mode, and the current injection window 13 and the gaps between the restriction layers ensure the lasing of the TE mode on both sides of the current injection area 11.

[0029] The implementation principle of a semiconductor laser with high polarization degree in the embodiment of the present application is as follows: the current is introduced from the P-side electrode 10 and finally led out from the N-side electrode 1. When the current passes through the ohmic contact layer 9, the conductivity of the direct contact between the P-side electrode 10 and the ohmic contact layer 9 is good, and the current can pass smoothly, and the restriction area 12 can limit the current passing through the area, thereby achieving the effect of suppressing the current, and then suppressing the TM mode on both sides of the current injection area 11, thereby improving the TE polarization degree.

[0030] Example 1: Reference Figure 4 In this embodiment, the restriction area 12 is composed of an insulating layer 14, and the insulating layer 14 is made of one of SiO2, Si3N4 or a composite film layer thereof, and has a thickness between 100-300nm. 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 area 11 for forming the restriction area 12. A portion of the P-side electrode 10 is directly in contact with the ohmic contact layer 9, and another portion is in contact with the insulating block 15. The insulating block 15 blocks the current passing through the area, thereby limiting the current.

[0031] Example 2: Reference Figure 5 The restriction area 12 in this embodiment is different from the restriction area 12 in the first embodiment: a plurality of grooves 16 are etched on the ohmic contact layer 9, and the highly doped portion of the upper restriction layer 8 is etched away, and the bottom of the groove 16 is located in the low-doped region of the upper restriction layer 8. The grooves 16 constitute the restriction area 12. Moreover, the doping concentration of the upper restriction layer 8 is lower than the doping concentration of the ohmic contact layer 9. The doping concentration of the ohmic contact layer 9 is 2E19-1E20cm -3 , 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 here makes the ohmic contact effect with the P-side electrode 10 thereon poor, and a higher series resistance is generated between the two, thereby reducing the injection of current to suppress the TM mode.

[0032] Embodiment 3: The difference between Embodiment 3 and Embodiment 2 is: Figure 6An insulating layer 14 is provided in the groove 16. The insulating layer 14 is made of SiO2, Si3N4 or a composite film thereof, and has a thickness between 100-300 nm. The insulating layer 14 can better limit the current in the groove 16, thereby improving the suppression effect on the TM mode.

[0033] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A semiconductor laser with high polarization degree, comprising 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) arranged in sequence from bottom to top, characterized in that: A current injection region (11) is provided on the ohmic contact layer (9), a plurality of restriction regions (12) are provided in the current injection region (11), the restriction regions (12) are symmetrically distributed on both sides of the current injection region (11), the restriction regions (12) are linearly distributed on both sides of the current injection region (11) to form restriction layers, multiple restriction layers are provided on each side of the current injection region (11), and gaps are left between the restriction layers, gaps are left between restriction regions (12) and restriction regions (12) in the same restriction layer to form current injection windows (13), and the restriction regions (12) in two adjacent restriction layers are arranged in an alternating manner.

2. A semiconductor laser with high polarization degree according to claim 1, characterized in that: The restriction zone (12) is arranged in a square shape, the width L1 of the restriction zone (12) is 5-500 μm, the height H2 is 5-50 μm, the horizontal spacing S1 between adjacent restriction zones (12) in the same restriction layer is 5-100 μm, the spacing S2 between adjacent restriction layers is 5-100 μm, the minimum distance d1 between the restriction zone (12) at the end of the current injection zone (11) and the end of the current injection zone (11) is 5-200 μm, and the minimum distance d2 between the restriction layer on the side of the current injection zone (11) and the side of the current injection zone (11) is 5-200 μm.

3. A semiconductor laser with high polarization degree according to claim 1, characterized in that: The height of the current injection region (11) is H1, and the sum of the heights of all the confinement layers on one side of the current injection region (11) is H3, wherein the ratio of H3 to H1 is between 1:10 and 1:

3.

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

5. A semiconductor laser with high polarization degree according to claim 1, characterized in that: A plurality of grooves (16) are etched on the ohmic contact layer (9), the bottom of the grooves (16) is an upper limiting layer (8), the doping concentration of the upper limiting layer (8) is lower than the doping concentration of the ohmic contact layer (9), and the grooves (16) constitute a limiting region (12).

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

7. A semiconductor laser with high polarization degree according to claim 5, characterized in that: The doping concentration of the ohmic contact layer (9) is 2E19-1E20cm -3 , with a thickness of 200nm-800nm, and the doping concentration of the upper limiting layer (8) is 5E17-1E19cm -3 .

8. A semiconductor laser with high polarization degree according to claim 4 or 6, characterized in that: The insulating layer (14) is made of a material selected from the group consisting of SiO2, Si3N4, or a composite film layer thereof.

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