阅读说明：本技术 一种发光均匀的顶发射垂直腔面发射激光器及其制备方法 (Top-emitting vertical-cavity surface-emitting laser with uniform light emission and preparation method thereof ) 是由 郑君雄 崔雨舟 冉宏宇 王青 于 2021-09-10 设计创作，主要内容包括：本发明提供一种发光均匀的顶发射垂直腔面发射激光器及其制备方法,该方法包括：在衬底上生长外延层(包括上下布拉格反射镜、缓冲层、有源层、过渡层、限制层、接触层)；通过光刻和干法刻蚀在外延层上形成台面结构；通过湿法处理对台面结构进行清洗；通过湿法氧化工艺氧化限制层,在中间形成出光孔；在获得的台面结构上镀膜金属形成上下电极。制备方法优点在于能够提高激光器出射激光的均匀性,并有效抑制氧化过程中出现的分层现象,从而提高顶发射垂直腔面发射激光器的可靠性和稳定性。通过本发明工艺制备得到的顶发射垂直腔面发射激光器克服了之前激光器出射光斑不均匀的问题,对开拓其在多个领域的应用十分有利。(The invention provides a top-emitting vertical cavity surface emitting laser with uniform light emission and a preparation method thereof, wherein the method comprises the following steps: growing an epitaxial layer (comprising an upper Bragg reflector, a lower Bragg reflector, a buffer layer, an active layer, a transition layer, a limiting layer and a contact layer) on a substrate; forming a mesa structure on the epitaxial layer by photolithography and dry etching; cleaning the mesa structure through wet processing; oxidizing the limiting layer through a wet oxidation process to form a light emitting hole in the middle; and plating metal on the obtained mesa structure to form an upper electrode and a lower electrode. The preparation method has the advantages that the uniformity of the laser emitted by the laser can be improved, and the layering phenomenon in the oxidation process is effectively inhibited, so that the reliability and the stability of the top emission vertical cavity surface emitting laser are improved. The top-emitting vertical cavity surface emitting laser prepared by the process overcomes the problem of uneven emergent light spots of the prior laser, and is very beneficial to developing the application of the top-emitting vertical cavity surface emitting laser in multiple fields.)

1. A top-emitting vertical cavity surface emitting laser with uniform light emission and a preparation method thereof are characterized in that:

growing an epitaxial layer on a substrate, wherein the epitaxial layer sequentially comprises a buffer layer, an N-type Bragg reflector, an active layer, a transition layer, a limiting layer, a P-type Bragg reflector and a contact layer from bottom to top;

forming a mesa structure on the epitaxial layer by photoetching and dry etching;

cleaning the mesa structure through wet processing to remove etching byproducts which are generated in the process of forming the mesa structure and are attached to the surface of the mesa structure and a passivation film deposited on the side wall of the mesa structure, wherein a cleaning agent used for removing the passivation film does not react with a semiconductor material;

oxidizing the limiting layer through a wet oxidation process to form a light emitting hole in the middle;

plating metal on the mesa structure to form an upper electrode and a lower electrode;

covering a transparent conductive film on the contact layer and the upper electrode on the upper surface;

the complete structure of the laser obtained finally comprises an N-type metal electrode, a substrate, a buffer layer, an N-type Bragg reflector, an active layer, a transition layer, a limiting layer, a P-type Bragg reflector, a contact layer, a P-type metal electrode and a transparent conductive film from bottom to top.

2. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the preparation method thereof as claimed in claim 1, wherein the surface roughness of the side wall of the mesa structure formed by dry etching is controlled below 15nm, and the verticality of the side wall is controlled at 85-90 degrees.

3. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the preparation method thereof as claimed in claim 2, wherein the mesa structure formed by dry etching has a passivation film deposited on its side wall during etching, and the presence of the passivation film can better control the surface roughness and the verticality of the side wall and simultaneously protect the mesa structure from lateral reaction.

4. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the manufacturing method thereof as claimed in claim 3, wherein before the wet oxidation process, a cleaning agent is further required to clean the mesa structure.

5. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the preparation method thereof as claimed in claim 4, wherein the time for cleaning the mesa structure by the cleaning agent is controlled within a range of 1-15 minutes according to the kinds of different cleaning agents.

6. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the manufacturing method thereof as claimed in claim 5, wherein the cleaning agent used includes but is not limited to neutral inorganic solvent, neutral organic solvent, acid-base solvent or solution, wherein the cleaning agent used for removing the passivation film does not react with the semiconductor material.

7. The top-emitting VCSEL and the manufacturing method thereof as claimed in claim 1, wherein a transparent conductive film is coated on the contact layer and the upper electrode, the transparent conductive film is electrically connected to the upper electrode, and the electrode structure is changed from a ring structure to a planar structure.

8. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the method for manufacturing the same as claimed in claim 7, wherein the transparent conductive film is an indium tin oxide film.

9. The top-emitting vertical cavity surface-emitting laser with uniform light emission and the method as claimed in claim 7, wherein the thickness of the transparent conductive film is controlled within the range of 100-800 nm.

Technical Field

The invention relates to the technical field of semiconductors, in particular to a top-emitting vertical cavity surface emitting laser with uniform light emission and a preparation method thereof.

Background

A Vertical-Cavity Surface-Emitting Laser (VCSEL) is a semiconductor Laser with a Laser Emitting direction perpendicular to a chip Surface, and compared with an edge-Emitting semiconductor Laser, a VCSEL has the advantages of small temperature drift, low threshold current, single longitudinal mode emission, small divergence angle, high modulation rate, easiness in high-speed communication, easiness in coupling a circular light spot with an optical fiber, low optical fiber transmission loss, easiness in packaging, easiness in two-dimensional integration, long service life and the like, and is deeply researched, and the application prospect in the field of high-speed optical communication is very good. The laser of the vertical cavity surface emitting laser is perpendicular to the surface of the chip and is emitted from the top surface or the bottom surface, the emitting direction is determined by the laser wavelength, and the optical communication application laser with the wavelength of 850nm generally adopts a top emitting structure.

A typical top-emitting vertical cavity surface-emitting laser has a basic structure including upper and lower N-type bragg mirrors each being a multilayer highly reflective film made of a material alternately changing in high and low refractive indices to achieve a reflectivity exceeding 99%, and an active region sandwiched therebetween, the refractive index of the upper P-type bragg mirror being relatively low, so that laser light exits from the upper surface. For the purpose of achieving a low threshold current, it is common practice to grow a limiting layer on the upper side or the lower side or both of the active region. In the preparation process of the laser, the periphery of the limiting layer is oxidized into an alumina insulating layer with low refractive index and high insulation through a wet oxidation process, the limiting layer which is not oxidized in the middle becomes a light emitting hole, so that a light path is limited in the middle of the limiting layer, and the aperture size of the light emitting hole in the limiting layer can be determined by controlling reaction parameters. The technology of introducing the limiting layer and controlling the size of the light-emitting hole can effectively reduce the threshold current of the device, improve the electro-optic conversion efficiency and play a great role in improving the performance of the laser.

However, the shape of the upper electrode of the vcsel laser is generally an annular structure, which facilitates the laser to emit from the middle and reduces the loss, but has the disadvantage of causing uneven electric field distribution, generally strong electric field strength near the electrode, weak electric field strength at the center of the vcsel relatively far from the electrode, uneven intensity distribution causing uneven spot distribution of the emitted laser light, forming an annular uneven spot with strong light intensity near the electrode and weak light intensity at the center far from the electrode, and seriously affecting the performance and practical application of the vcsel. In addition, because some cleaning agents can react with the materials forming the laser in the cleaning process, after the cleaning and oxidation processes are finished, because the oxidation rates of different materials are different from the reaction rate of the cleaning agents, the surface of the side wall of the laser can become uneven, namely, the layering phenomenon occurs, and the layering phenomenon can greatly influence the reliability and the stability of the product. Therefore, in order to solve these problems, it is necessary to develop a novel top emission vertical cavity surface emitting laser with uniform light emission and a fabrication scheme thereof. .

Disclosure of Invention

The method can prepare the laser with uniform emergent light spots, and can avoid the occurrence of layering phenomenon by controlling the oxidation process, thereby improving the reliability and stability of the product and being beneficial to developing the application range.

The preparation method provided by the invention comprises the following steps: growing an epitaxial layer on a substrate, wherein the epitaxial layer is sequentially provided with a buffer layer, an N-type Bragg reflector, an active layer, a transition layer, a limiting layer, a P-type Bragg reflector and a contact layer from bottom to top; forming a mesa structure on the epitaxial layer by photoetching and dry etching, and adding nitrogen into etching gas in the etching process so as to deposit and form a protective film on the side wall of the mesa structure; cleaning the mesa structure through wet processing to remove etching byproducts which are generated and attached to the surface in the process of forming the mesa structure and a passivation film deposited on the side wall; oxidizing the periphery of the limiting layer by a wet oxidation process to form a light outlet hole in the middle; forming an upper metal electrode and a lower metal electrode on the mesa structure through film coating; and a transparent conductive film is covered on the annular metal electrode and the contact layer on the upper surface.

The structure of the vertical cavity surface emitting laser is respectively an N-type metal electrode, a substrate, a buffer layer, an N-type Bragg reflector, an active layer, a transition layer, a limiting layer, a P-type Bragg reflector, a contact layer, a P-type metal electrode and a transparent conductive film from bottom to top.

Before the step of forming the light-emitting hole in the limiting layer through a wet oxidation process, the side walls of the P-type Bragg reflector, the N-type Bragg reflector and the active region clamped between the P-type Bragg reflector and the N-type Bragg reflector are protected by the nitrogen-containing passivation film deposited in the etching process, a cleaning agent which does not react with a laser material is used in the cleaning process to remove the protective film, then the oxidation is carried out immediately, and the delamination phenomenon can be inhibited to the maximum extent. The time of the cleaning treatment is 1 to 15 minutes. The cleaning agent used comprises a neutral inorganic solvent, a neutral organic solvent, an acid-base solvent or a solution (the cleaning agent does not react with the semiconductor material, particularly the active layer and the confinement layer material). The transparent conductive film covers the upper electrode and the contact layer exposed in the middle. The transparent conductive film is electrically connected to the upper electrode. The transparent conductive film is an ITO film with a thickness of 100-800 nm. The transparent conductive film is introduced, so that the laser transmittance of the transparent conductive film is over 95 percent, laser emission is not influenced, and more importantly, the transparent conductive film is introduced, so that the annular electrode structure on the upper surface is changed into a planar electrode structure, the problem of uneven light intensity distribution of emitted laser is solved, and the application prospect of the vertical cavity surface emitting laser is greatly expanded. The method is not only suitable for the top emission structure, but also suitable for the bottom emission structure.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

fig. 1 is a schematic structural view of a top-emitting vertical cavity surface-emitting laser according to the present invention.

In the figure: 1. an N-type metal electrode; 2. a substrate; 3. a buffer layer; 4. an N-type Bragg reflector; 5. an active layer; 6. a transition layer; 7. a confinement layer; 8. a P-type Bragg reflector; 9. a contact layer; 10. a P-type metal electrode; 11. a transparent conductive film.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

Example (b): as shown in fig. 1, the top-emitting vertical cavity surface-emitting laser according to the present invention has a structure including, from bottom to top, an N-type metal electrode 1, a substrate 2, a buffer layer 3, an N-type bragg reflector 4, an active layer 5, a transition layer 6, a confinement layer 7, a P-type bragg reflector 8, a contact layer 9, a P-type metal electrode 10, and a transparent conductive film 11. The materials of each structure are respectively as follows: the N-type metal electrode 1 is a titanium platinum alloy and is a surface electrode; the substrate 2 is a gallium arsenide substrate and is doped with silicon; the buffer layer 3 is aluminum-doped gallium arsenide; the N-type Bragg reflector 4 is of an aluminum gallium arsenide multilayer alternating structure with different aluminum components and is doped with silicon; undoped aluminum-gallium arsenide with gradually changed aluminum components grows between the N-type Bragg reflector 4 and the active region, and the undoped aluminum-gallium arsenide has the functions of reducing stress and improving the lattice quality of the quantum well of the active region; the active layer 5 comprises a quantum well and a phase matching layer, and the indium gallium arsenide/aluminum gallium arsenide multi-quantum well structure adopted by the invention has the advantages of higher bandwidth, lower threshold current and the like compared with the traditional gallium arsenide/aluminum gallium arsenide quantum well structure; the transition layer 6 and the limiting layer 7 are aluminum gallium arsenide with different components and are used for limiting current and an optical field; the P-type Bragg reflector 8 is of an aluminum gallium arsenide multilayer alternating structure with different aluminum components and is doped with carbon; the contact layer 9 is gallium arsenide, which is used as ohmic contact; the P-type metal electrode 10 is made of gold-germanium-nickel alloy and is a ring electrode; the transparent conductive film 11 is an indium tin oxide film.

The preparation process comprises the following steps: firstly, sequentially growing each epitaxial structure on a substrate 2 to obtain an epitaxial wafer; obtaining a mesa structure of the laser by photoetching and dry etching processes, and removing etching byproducts and a passivation film on the side wall attached to the mesa structure by cleaning treatment; carrying out lateral oxidation on the limiting layer 7 through a wet oxidation process to form a light emitting hole in the middle; and growing metal electrodes on the upper surface and the lower surface, completing a rapid annealing process, and finally covering a transparent conductive film 11 on the upper electrode and the contact layer 9 to obtain the final top-emitting vertical cavity surface-emitting laser device.

A transparent conductive film 11 is covered on the annular P-type metal electrode 10, the transmittance of the corresponding laser wavelength is more than 95%, and the laser emission is not influenced. The transparent conductive film 11 is electrically connected with the annular metal electrode, the annular electrode is changed into a planar electrode, the electric field distribution of the laser emergent surface is uniform, and the intensity uniformity of emergent light spots is realized.

In addition, since part of the cleaning agent has the property of corroding the semiconductor, the side wall of the mesa structure becomes uneven after the cleaning process is finished, and a delamination phenomenon occurs, which affects the reliability and stability of the laser. Therefore, in the application, the table-board structure is cleaned by adopting a cleaning agent which does not react with the laser material, namely, the cleaning agent for removing the limiting layer 7 and the passivation film deposited on the side wall of the Bragg reflector does not react with the device material, the layering phenomenon is inhibited, and the performance and the stability of the laser are greatly improved.

Finally, it should be noted that: in the description of the present invention, it should be noted that the terms "vertical", "upper", "lower", "horizontal", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.