A single mode low divergence vertical cavity surface emitting laser

Abstract

The application relates to the technical field of semiconductor lasers, in particular to a single-mode low-divergence vertical-cavity surface-emitting laser. The laser comprises, from bottom to top, a substrate, an N-type DBR layer, a multi-quantum-well active region, a current-limiting layer, a spacing layer, a concave etching layer and a concave dielectric-film DBR layer which are tightly stacked in sequence; the concave etching layer and the concave dielectric-film DBR layer are concave to the spacing layer direction, and jointly form a concave mirror for filtering high-order modes; a P-type contact electrode is arranged on the concave etching layer and serves as a positive electrode; an N-type contact electrode is stacked on the surface of the substrate away from the N-type DBR layer and forms a negative electrode. The advantage lies in that the concave mirror is arranged in the VCSEL cavity to increase the loss of high-order modes, suppress the generation of high-order modes and reduce the divergence angle; meanwhile, the concave mirror has a strong suppression on high-order modes, and compared with the prior art, the size of the oxidation hole can be increased and the power of the VCSEL can be improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to a single-mode low-divergence-angle vertical-cavity surface-emitting laser. Background Technology

[0002] Vertical-cavity surface-emitting lasers (VCSELs) possess numerous advantages, including low threshold current, circular spot size, high modulation bandwidth, single longitudinal mode lasing, ease of fabrication into high-density two-dimensional arrays, and relatively low manufacturing cost. They are widely used in many fields, particularly playing a crucial role in fiber optic communication. However, due to their large transverse width, VCSELs typically operate with multiple transverse modes, resulting in poor coherence and a large divergence angle in the output laser. To achieve fundamental mode lasing, a common method is to limit higher-order transverse modes by fabricating small current injection apertures, typically using wet nitrogen oxidation, proton bombardment, or buried heterojunctions. However, simply reducing the current injection aperture to control modes significantly increases the device's series resistance, leading to overheating and failure. Furthermore, reducing the area of ​​the current injection region is detrimental to achieving high-power lasing in VCSELs. Other VCSEL mode control methods exist, such as surface relief designs and anti-waveguide structures. A common problem with these methods is that the microstructures controlling the modes are fabricated on the device surface. While the fabrication process is simple, the difference in loss introduced between modes is relatively small. During operation, as the current increases, higher-order modes in a VCSEL tend to achieve higher gains, leading to lasing and the formation of multimode. How to enable a VCSEL to possess fundamental mode and low divergence angle output characteristics through effective, reliable, and simple structures and processes is a technical problem that those skilled in the art need to solve. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a single-mode, low-divergence-angle vertical-cavity surface-emitting laser.

[0004] The present invention aims to provide a single-mode low divergence angle vertical cavity surface-emitting laser, comprising a substrate, an N-type DBR layer, a multi-quantum well active region, a current confinement layer, a spacer layer, a concave etched layer, and a concave dielectric film DBR layer stacked tightly from bottom to top;

[0005] The concave etched layer and the concave dielectric film DBR layer are recessed towards the spacer layer to form a concave reflector, which is used to filter out higher-order modes.

[0006] The concave etched layer is provided with a P-type contact electrode, which serves as the positive electrode; the N-type contact electrode is stacked on the side surface of the substrate away from the N-type DBR layer to form the negative electrode.

[0007] Preferably, the focal point of the concave mirror is aligned with the center of the oxide hole in the current-limiting layer.

[0008] Preferably, the material of the current-limiting layer is oxidized Al. x Ga 1-x As is used to restrict the flow path of injected charge carriers; the pore size of the oxide holes in the current-limiting layer is greater than 4 micrometers.

[0009] Preferably, the material of the concave etching layer is GaAs.

[0010] Preferably, the spacer layer is made of Al. x Ga 1-x As is used to adjust the distribution of the optical field within the cavity, so that the active region of the multi-quantum well is located at the position of the strong optical field within the cavity, thereby increasing the confinement factor of the optical field.

[0011] Preferably, the material for the active region of the multi-quantum well is GaAs / Al. x Ga 1-x As.

[0012] Preferably, the N-type DBR layer is an Al with high and low Al composition. x Ga 1-x As semiconductor materials.

[0013] Preferably, the concave dielectric film DBR layer is an oxide dielectric film, arranged in a periodic pattern of high and low refractive indices, with each layer grown to a thickness equal to one-quarter of the optical thickness; the material of the concave dielectric film DBR layer includes two of Si, SiO2, HfO2, and Al2O3; the period is 8 to 9.

[0014] Preferably, the substrate is a group III-V semiconductor material.

[0015] Preferably, the P-type contact electrode has a Ti / Pt / Au three-layer structure.

[0016] Preferably, the N-type contact electrode has an Au-Ge / Ni / Au structure.

[0017] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0018] The technical solution of this invention uses a concave mirror inside the VCSEL cavity to diverge higher-order modes, increasing the loss of higher-order modes. The concave mirror also has a strong interaction between modes within the VCSEL cavity, resulting in greater loss for higher-order modes and further suppressing their generation. Meanwhile, the fundamental mode, due to its smaller divergence angle and mode distribution near the optical axis, experiences almost no loss from the concave structure, thus reducing the divergence angle. Simultaneously, because the concave mirror strongly suppresses higher-order modes, compared to existing technologies, it allows for larger oxide apertures and increased VCSEL injection current, thereby increasing the VCSEL power. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a fundamental mode vertical cavity surface-emitting laser structure provided according to an embodiment of the present invention.

[0020] Figure label:

[0021] 1. Substrate; 2. N-type DBR layer; 3. Multiple quantum well active region; 4. Current confinement layer; 5. Spacer layer; 6. Concave etched layer; 7. Concave dielectric DBR layer; 8. P-type contact electrode; 9. N-type contact electrode. Detailed Implementation

[0022] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0024] The present invention provides a single-mode low divergence angle vertical cavity surface-emitting laser, comprising a substrate, an N-type DBR layer, a multi-quantum well active region, a current confinement layer, a spacer layer, a concave etched layer, and a concave dielectric film DBR layer stacked tightly from bottom to top;

[0025] The concave etched layer and the concave dielectric film DBR layer are recessed towards the spacer layer to form a concave reflector, which is used to filter out higher-order modes.

[0026] The concave etched layer is provided with a P-type contact electrode, which serves as the positive electrode; the N-type contact electrode is stacked on the side surface of the substrate away from the N-type DBR layer to form the negative electrode.

[0027] The focal point of the concave mirror is aligned with the center of the oxide hole in the current-limiting layer.

[0028] The N-type DBR layer is a multi-period N-type DBR structure with alternating growth of high and low refractive index semiconductor materials, and each layer is grown with a thickness of one-quarter of the optical thickness.

[0029] The multi-quantum-well active region is an active region structure composed of multiple quantum well structures, used to generate the optical gain required to form laser light.

[0030] The current limiting layer is an insulating layer used to restrict the flow path of injected charge carriers;

[0031] The spacer layer is used to adjust the optical field distribution inside the VCSEL cavity, so that the multi-quantum well active region is located at the position of strong optical field inside the cavity, thereby increasing the confinement factor of the optical field.

[0032] The concave etching layer has an inner concave structure, which can be realized by utilizing the isotropic principle of wet etching.

[0033] The concave dielectric film DBR layer is an oxide dielectric film, arranged in a periodic pattern of high and low refractive indices. Each layer is grown with a thickness of one-quarter of the optical thickness. The top DBR (optional materials include Si, SiO2, HfO2, Al2O3, etc.) has a lower reflectivity than the N-type DBR layer, allowing laser light to exit from the concave dielectric film DBR layer.

[0034] The P-type contact electrode and the N-type contact electrode correspond to the positive and negative electrodes of the fundamental mode vertical cavity surface-emitting laser, respectively.

[0035] In a specific embodiment, the substrate is a group III-V semiconductor material; preferably GaN, GaAs, InP, or GaSb.

[0036] In a specific embodiment, the N-type DBR layer is an Al layer with high and low Al composition. x Ga 1-x As semiconductor material, typically high Al content x = 0.9, low Al content x = 0.1, typical number of cycles is about 32, each layer is grown with a thickness of one-quarter of the optical thickness of the material, and reflectivity > 99.5%;

[0037] In a specific embodiment, the active region of the multi-quantum well is GaAs / Al. x Ga 1-x As, x = 0.2~0.3, by adjusting the thickness of the trap or the Al composition of the barrier, the emission band coverage of the active region can be tuned to 850nm;

[0038] In a specific embodiment, the current-limiting layer is formed by lateral wet oxidation of Al with a high Al content. x Ga 1-xAs is formed, Al = 0.98; or by using proton bombardment, an insulating region with high resistivity is formed at the target depth, creating current confinement. Typical protons include hydrogen and zinc.

[0039] In a specific embodiment, the spacer layer is made of Al x Ga 1-x As is the constituent, x = 0.3 to 0.4;

[0040] In a specific embodiment, the material of the concave etching layer is GaAs;

[0041] In a specific embodiment, the concave dielectric film DBR layer is achieved by alternating growth of Si and SiO2, with each layer having a thickness of one-quarter of the optical thickness of the material, and a typical period of about 8 to 9.

[0042] In a specific embodiment, the P-type contact electrode has a Ti / Pt / Au three-layer structure; the N-type contact electrode has an Au-Ge / Ni / Au structure.

[0043] The VCSEL structure of this invention uses a concave mirror inside the cavity to diverge higher-order modes, increasing the loss of these modes. Because the concave mirror structure is inside the VCSEL cavity, its interaction with the modes is strong, resulting in lower loss for higher-order modes. Meanwhile, the fundamental mode, due to its smaller divergence angle and mode distribution near the optical axis, experiences almost no loss due to the concave structure. Therefore, the concave structure effectively increases the loss of higher-order modes, ensuring that the fundamental mode can always reciprocate within the VCSEL resonant cavity to achieve stimulated amplification, while other higher-order modes are suppressed, thus reducing the divergence angle. Simultaneously, because the concave mirror strongly suppresses higher-order modes, compared to existing technologies, the size of the oxide aperture and the VCSEL injection current can be increased. While increasing the VCSEL injection current results in a carrier distribution in the injection region that is high at both ends and low in the middle, higher-order modes in this region will not generate lasing, thus preventing an increase in the number of modes. This, in turn, increases the power of the VCSEL.

[0044] Example 1

[0045] Figure 1 A single-mode low divergence angle vertical cavity surface-emitting laser is shown, comprising a substrate 1, an N-type DBR layer 2, a multi-quantum well active region 3, a current confinement layer 4, a spacer layer 5, a concave etched layer 6, and a concave dielectric film DBR layer 7, which are tightly stacked from bottom to top.

[0046] The concave etching layer 6 is used together with the concave dielectric film DBR layer 7 to form a concave reflector, thereby achieving the filtering of higher-order modes; the focal point of the concave reflector and the center of the oxide hole of the current limiting layer 4 are on a straight line.

[0047] A P-type contact electrode 8 is provided on the concave etched layer 6 as the positive electrode; an N-type contact electrode 9 is stacked on the side surface of the substrate 1 away from the N-type DBR layer 2 to form the negative electrode.

[0048] The material of substrate 1 is GaAs;

[0049] N-type DBR layer 2 is an Al layer with high and low Al composition. x Ga 1-x As semiconductor material, with high Al content x = 0.9, low Al content x = 0.1, 32 cycles, each layer grown to a thickness of one-quarter of the optical thickness of the material, and reflectivity > 99.5%;

[0050] The material of the active region 3 of the multi-quantum well is GaAs / Al 0.2 Ga 0.8 As;

[0051] The material of current-limiting layer 4 is oxidized Al. 0.98 Ga 0.02 As;

[0052] The pore size of the oxide pores is greater than 4 micrometers;

[0053] The material of spacer layer 5 is Al 0.3 Ga 0.7 As;

[0054] The material of the concave etching layer 6 is GaAs;

[0055] The concave dielectric film DBR layer 7 is an oxide dielectric film with alternating growth of Si and SiO2. Each layer is one-quarter of the optical thickness of the material, with a typical period of 8. Its reflectivity is lower than that of the N-type DBR layer 2, allowing the laser to be emitted from the concave dielectric film DBR layer 7.

[0056] P-type contact electrode 8 has a Ti / Pt / Au three-layer structure; N-type contact electrode 9 has an Au-Ge / Ni / Au structure.

[0057] In the prior art, the diameter of the oxide pore is less than 4 micrometers to limit higher-order modes. In this embodiment, the concave etching layer 6 is used together with the concave dielectric film DBR layer 7 to form a concave reflector, which has a strong filtering effect on higher-order modes, thereby increasing the pore size of the oxide pore and thus obtaining higher power.

[0058] Example 2

[0059] A method for fabricating a single-mode, low-divergence-angle vertical-cavity surface-emitting laser (VCSEL) specifically includes the following steps:

[0060] S1. AlxGa1-xAs semiconductor materials with high and low Al compositions are alternately epitaxially grown on substrate 1 using MOCVD method to form N-type DBR layer 2;

[0061] S2. Epitaxially grow a multi-quantum-well active region 3 on the N-type DBR layer 2;

[0062] S3. Epitaxial growth of Al on the multi-quantum-well active region 3 0.98 Ga 0.02 As;

[0063] S4, Continue epitaxial growth of spacer layer 5;

[0064] S5. Epitaxially grow GaAs material on spacer layer 5;

[0065] S6. The sample is coated with resist, photolithographically etched, and developed to form a mesa structure pattern. The mesa structure is then dry-etched using an ICP etching device until the Al described in step S3 is exposed. 0.98 Ga 0.02 For As material, the etching gases are Cl2 / BCl3 / Ar;

[0066] S7. Wet oxidation equipment is used to process Al in a high temperature and high humidity environment. 0.98 Ga 0.02 The As material is laterally oxidized to form a current confinement layer 4; the current confinement layer 4 is a confinement structure for injected carriers, and the diameter of the formed aperture can be controlled by the oxidation time.

[0067] S8. A second photolithography process is performed, followed by spin coating, photolithography, and development steps to form the concave etched layer 6. The GaAs material grown in step S5 is wet-etched using a wet etching solution. By adjusting the ratio of the etching solution, isotropic etching can be achieved, ultimately forming the concave etched layer 6. The wet etching solution is a hydrogen peroxide-based solution containing phosphoric acid, sulfuric acid, or nitric acid.

[0068] S9. Perform a third photolithography using negative photoresist to create the electrode pattern; deposit P-type metal on the photolithographically developed sample using magnetron sputtering equipment, and place the deposited sample in an acetone solution for a lift-off process to form P-type contact electrode 8.

[0069] S10. Perform the fourth photolithography using negative photoresist. After photolithography and development, use an electron beam evaporation device to alternately grow and deposit Si and SiO2 on the sample. Perform a lift-off process on the evaporated sample in acetone solution to remove unwanted parts and form a concave dielectric film DBR layer 7.

[0070] S11. Thin and polish the substrate 1, and then use electron beam evaporation to deposit the N-type contact electrode 9 to complete the fabrication of the entire structure.

[0071] Example 3

[0072] A method for fabricating a single-mode, low-divergence-angle vertical-cavity surface-emitting laser differs from Example 2 in that the current-limiting layer 4 in step S7 is fabricated using a proton bombardment process to form an insulating region with high resistivity at the target depth, thereby creating current limitation; the protons are hydrogen, zinc, etc.; step S9 uses electron beam evaporation to fabricate the P-type contact electrode 8; the remaining fabrication steps are the same.

[0073] The fabrication process of the mechanism of the present invention is simple and consists of conventional semiconductor processes, which can ensure good reliability and repeatability.

[0074] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0075] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A single-mode, low-divergence-angle vertical-cavity surface-emitting laser, characterized in that: It includes a substrate, an N-type DBR layer, a multi-quantum well active region, a current confinement layer, a spacer layer, a concave etched layer, and a concave dielectric DBR layer, which are stacked tightly from bottom to top. The spacer layer is made of Al x Ga 1-x Composed of As, x = 0.3~0.4; The pore size of the oxide holes in the current-limiting layer is greater than 4 micrometers; the current-limiting layer is an insulating layer used to limit the flow path of injected charge carriers. The material of the concave etching layer is GaAs; The concave etched layer and the concave dielectric film DBR layer are recessed towards the spacer layer to form a concave reflector, which is used to filter out higher-order modes and reduce the divergence angle; the focal point of the concave reflector is on the same straight line as the center of the oxide hole of the current limiting layer. The concave etched layer is provided with a P-type contact electrode, which serves as the positive electrode; an N-type contact electrode is stacked on the side of the substrate away from the N-type DBR layer to form the negative electrode. The concave dielectric film DBR layer is achieved by alternating growth of Si and SiO2, with each layer having a thickness of one-quarter of the optical thickness of the material.

2. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 1, characterized in that: The material of the current limiting layer is oxidized Al. x Ga 1-x As.

3. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 1, characterized in that: The spacer layer is used to adjust the distribution of the optical field inside the cavity, so that the active region of the multi-quantum well is located at the position of strong optical field inside the cavity, thereby increasing the confinement factor of the optical field.

4. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 3, characterized in that: The active region of the multi-quantum-well is made of GaAs / Al. x Ga 1-x As.

5. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 4, characterized in that: The N-type DBR layer is an Al layer with high and low Al composition. x Ga 1-x As semiconductor materials.

6. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 5, characterized in that: The concave dielectric film DBR layer is arranged in a periodic pattern of high and low refractive indices; the period of the concave dielectric film DBR layer is 8~9.

7. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 6, characterized in that: The substrate is a III-V group semiconductor material.

8. A single-mode low-divergence-angle vertical-cavity surface-emitting laser according to claim 7, characterized in that: The P-type contact electrode has a Ti / Pt / Au three-layer structure; the N-type contact electrode has an Au-Ge / Ni / Au structure.

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