CN114256738B - An electrically pumped nitride suspended waveguide microlaser and its preparation method - Google Patents

Abstract

The invention discloses an electrically pumped nitride suspended waveguide microlaser and a preparation method thereof. The present invention uses photolithography, ICP nitride dry etching, silicon wet etching process, and electron beam evaporation process to prepare a nitride microcavity laser with a suspended waveguide structure on a silicon substrate nitride epitaxial wafer; the microcavity is suspended , the optical loss in the vertical direction is greatly reduced. At the same time, the electrode light-emitting area coincides with the microcavity area, and the leads are on the pillars at both ends, avoiding complicated lead processes.

Description

An electrically pumped nitride suspended waveguide microlaser and its preparation method

Technical field

The invention relates to the field of laser technology, and in particular to an electrically pumped nitride suspended waveguide microlaser and a preparation method thereof.

Background technique

Laser technology is widely used in the development of the national economy, involving industrial manufacturing, communications, information processing, medical and health, energy conservation and environmental protection, aerospace and other fields. It is a key supporting technology for the development of high-end precision manufacturing and helps the country's industrial transformation and upgrading. As one of the advanced technologies of modern manufacturing industry, it has the advantages of high precision, high efficiency, low energy consumption and low cost that traditional processing methods do not have. It has great changes in the material, shape, size and processing environment of processing materials. The degree of freedom can better solve technical problems such as processing, forming and refining of different materials. With the continuous development of laser technology and laser micromachining application technology, laser processing technology can replace traditional mechanical processing in more fields.

According to different working media, lasers can be divided into the following categories: solid lasers, liquid lasers, gas lasers, semiconductor lasers, and free electron lasers. Semiconductor lasers have outstanding characteristics such as high energy conversion efficiency, easy high-speed current modulation, ultra-miniaturization, simple structure, and long service life, making them the most important and most valuable type of laser.

So far, researchers have proposed different forms of lasers, mainly in the following directions: semiconductor lasers, fiber lasers, and solid lasers. Both fiber and solid-state lasers rely on the development of semiconductor lasers. In solid-state lasers, LDs are usually fiber-coupled. The energy of a single tube is small and the beam quality is not good. Generally, the output is coupled to the fiber in a shaping manner to improve the beam. Quality; the same goes for fiber lasers, which also use LD as the pump source. The improvement of power efficiency and simplification of the system also rely on the development of LD chips; for the pump source, the biggest difference between optical pumping and electrical pumping is that, Electrical pumping is more efficient, smaller, and can reach wavelengths that cannot be reached by optical pumping.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention provides an electrically pumped nitride suspended waveguide microlaser with low optical loss in the vertical direction, which is conducive to high-density on-chip integration and extremely efficient. It also provides a simple process flow and small mode volume. Preparation method of electrically pumped nitride suspended waveguide structure microlaser with low surface roughness.

According to one aspect of the present invention, an electrically pumped nitride suspended waveguide microlaser is provided. The laser uses a silicon-based nitride epitaxial wafer as a carrier and includes a silicon substrate layer arranged sequentially from bottom to top. The u-type gallium nitride layer, the n-type gallium nitride layer, the quantum well layer, the p-type gallium nitride layer on the surface, the p-type electrode provided on the p-type gallium nitride layer, and the n-type gallium nitride layer on the surface. n-type electrode on the upper surface of the gallium layer; the laser has a waveguide microcavity structure including a positive disk microcavity and a negative disk microcavity, and the positive disk microcavity and the negative disk microcavity are connected by a waveguide , the lower parts of the positive disk microcavity and the negative disk microcavity are respectively supported by a silicon substrate layer.

The silicon substrate layer in the above technical solution has been etched by a mixed solution of HF and HNO _3. Due to isotropy, a disc microcavity structure is formed with only silicon pillars supporting both sides of the waveguide, so that the two disc microcavities are connected. The waveguide structure is completely suspended, greatly reducing optical loss in the vertical direction.

Furthermore, the structure of the positive disk microcavity penetrates the p-type gallium nitride layer 5 and the quantum well layer 4 .

Further, the p-type electrode 6, p-type gallium nitride layer 5 and quantum well layer 4 are provided in the positive disk microcavity; the n-type electrode 7 and n-type gallium nitride layer 3 are provided in the negative disk microcavity. cavity.

Further, the positive disk microcavity and the negative disk microcavity are in the shape of steps.

Further, the n-type electrode 7 is formed at the center of the negative electrode disc microcavity; the p-type electrode 6 is formed at the center of the positive electrode disc microcavity.

According to one aspect of the present invention, a method for preparing the electrically pumped nitride suspended waveguide microlaser is provided, including:

Step 1: Spin-coat photoresist on the upper surface of the p-type gallium nitride layer 5 of the silicon-based nitride epitaxial wafer, and then use a photolithography process to define the pattern of the cathode disk microcavity on the spin-coated photoresist layer. ;

Step 2: Use electron beam evaporation process to evaporate metallic nickel on the pattern of the positive electrode disk microcavity, and remove the remaining photoresist;

The third step: Use the ICP etching process to etch down the nitride layer until the upper surface of the n-type gallium nitride layer 3, thereby transferring the pattern structure defined in the first step downward to the silicon-based nitride. In the p-type gallium nitride layer 5 and quantum well layer 4 of the epitaxial wafer, the metallic nickel is then removed with dilute nitric acid;

Step 4: Spin-coat photoresist on the upper surface of the silicon-based nitride epitaxial wafer, and then use photolithography technology to define the pattern of the negative electrode disk microcavity on the spin-coated photoresist layer;

Step 5: Use the electron beam evaporation process to evaporate metallic nickel on the surface of the pattern structure of the negative electrode disk microcavity, and remove the remaining photoresist;

Step 6: Use the ICP etching process to etch down the n-type gallium nitride layer 3 along the defined structure of the complete negative electrode disk microcavity to the upper surface of the silicon substrate layer 1, thereby removing the complete negative electrode disk. The pattern structure of the disk microcavity is transferred to the n-type gallium nitride layer 3 and the u-type gallium nitride layer 2 in sequence, and finally the metallic nickel is removed with dilute nitric acid;

Step 7: Spin-coat photoresist on the upper surface of the silicon-based nitride epitaxial wafer, use photolithography technology, and define p-type region electrode patterns and n-type region electrode patterns on the spin-coated photoresist layer;

Step 8: Use an electron beam evaporation process to evaporate a positive electrode on the upper surface of the p-type region electrode pattern, and evaporate a negative electrode on the upper surface of the n-type region electrode pattern, so that the p-type gallium nitride layer 5 and the n-type nitride layer are Positive and negative electrodes are plated on the gallium layer 3 respectively, and finally the remaining photoresist is removed, and the Au/Ni on the photoresist is peeled off to obtain p-type electrode 6 and n-type electrode 7;

Step 9: Use isotropic wet etching of the silicon substrate layer 1 to form silicon pillars supporting the disks on both sides of the waveguide, thereby obtaining a completely suspended waveguide microcavity.

The above technical solution uses advanced micro-nano processing technology to design and prepare an electrically driven gallium nitride suspended waveguide microcavity. Since the suspended waveguide structure only has a disk microcavity connected at both ends supported by a silicon substrate layer underneath, the two circles are connected. The waveguide microcavity structure of the disk is completely suspended, which greatly reduces the optical loss in the vertical direction and further reduces the system cost by avoiding complex wiring processes.

Further, both the positive electrode and the negative electrode are evaporated Au/Ni.

Compared with the existing technology, the beneficial effects of the present invention include:

(1) The present invention is a laser based on a gallium nitride material system. Compared with solid lasers using crystals and glass as matrix materials and gas lasers using gas as the working medium, the wavelength of the semiconductor laser can be extended to the visible spectrum. and ultraviolet spectral range; and, as a representative of Group III nitride wide band gap semiconductors, gallium nitride has significant performance advantages compared with the previous two generations of semiconductors, overcoming the narrow band gap and low electron mobility of silicon materials. There are many restrictive issues in the high-frequency and high-power fields. It has a low-dimensional quantum structure and excellent optoelectronic physical properties. Furthermore, because gallium nitride is a good optoelectronic material, it can more intuitively reflect the luminous color of the microcavity. The change.

(2) The present invention uses photolithography, ICP nitride dry etching, silicon wet etching process, and electron beam evaporation process to prepare a nitride microcavity laser with a suspended waveguide structure on a silicon substrate nitride epitaxial wafer. The waveguide The microcavity is suspended in the air, and the optical loss in the vertical direction is extremely small. At the same time, the electrode light-emitting area coincides with the microcavity area, and the leads are on the pillars at both ends, avoiding complex lead processes.

(3) The electrically pumped nitride suspended waveguide microlaser provided by the present invention has low optical loss in the vertical direction, which is conducive to high-density on-chip integration and is extremely efficient; the preparation method provided by the present invention has a simple process flow and can prepare a pattern with small volume and surface Low roughness nitride suspended waveguide structure electrically pumped laser.

Description of drawings

Figure 1 is a side view of an electrically pumped nitride suspended waveguide microlaser according to an embodiment of the present invention;

Figure 2 is a top view of an electrically pumped nitride suspended waveguide microlaser according to an embodiment of the present invention;

Figure 3 is a flow chart of a manufacturing process of an electrically pumped nitride suspended waveguide microlaser according to an embodiment of the present invention.

In the picture: 1. Silicon substrate layer; 2. U-type gallium nitride layer; 3. n-type gallium nitride layer; 4. Quantum well layer; 5. p-type gallium nitride layer; 6. p-type electrode; 7. n-type electrode.

Detailed ways

The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present invention.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " The directions indicated by "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" etc. or The positional relationship is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, Therefore, it should not be construed as a limitation of the present invention. In addition, the terms “first” and “second” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Thus, features defined as “first” and “second” may explicitly or implicitly include one or more of the described features. In the description of the present invention, "plurality" means two or more than two, unless otherwise explicitly and specifically limited.

In the description of the present invention, it should be noted that, unless otherwise clearly stated and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection. Connection, or integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or it can be an indirect connection through an intermediary, it can be an internal connection between two elements or an interaction between two elements relation. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

In the present invention, unless otherwise expressly provided and limited, the term "above" or "below" a first feature of a second feature may include direct contact between the first and second features, or may also include the first and second features. Not in direct contact but through additional characteristic contact between them. Furthermore, the terms "above", "above" and "above" a first feature on a second feature include the first feature being directly above and diagonally above the second feature, or simply mean that the first feature is higher in level than the second feature. “Below”, “under” and “under” the first feature is the second feature includes the first feature being directly below and diagonally below the second feature, or simply means that the first feature is less horizontally than the second feature.

Example 1

As shown in Figure 1-2, this embodiment provides an electrically pumped nitride suspended waveguide microlaser, using a silicon-based nitride epitaxial wafer as a carrier, including a silicon substrate layer 1, a u-type gallium nitride layer 2, an n-type nitrogen The gallium nitride layer 3 , the quantum well layer 4 provided on one side of the n-type gallium nitride layer 3 , and the p-type gallium nitride layer 5 . The n-type gallium nitride platform is in a stepped shape with the p-type gallium nitride platform on the other side. An n-type electrode 7 of Au/Ni is evaporated on the upper surface of the exposed n-type gallium nitride layer 3 in the center of the disk, and a deposited metal material is evaporated on the waveguide and disk patterns of the p-type gallium nitride platform. It is a p-type electrode 6 of Au/Ni. The silicon substrate layer 1 has been etched by a mixed solution of HF and HNO _3. Due to isotropy, a disk is formed only supported by silicon pillars, making the waveguide structure completely suspended and the optical loss in the vertical direction is small.

The waveguide structure and the right disc structure penetrate the p-type gallium nitride layer 5 and the quantum well layer 4 .

The p-type electrode 6 is arranged along the upper surface of the p-type gallium nitride layer 5, with a waveguide and a disk structure connected to the right below it; the n-type electrode 7 is arranged along the upper surface of the n-type gallium nitride layer 3, with a waveguide structure below it. Connected discs on the left.

Example 2

As shown in Figure 3, this embodiment takes the preparation of a disk + waveguide microcavity structure as an example to prepare an electrically pumped nitride suspended waveguide microlaser, in which the disk radius is 75 microns, the waveguide length is 200 microns, and the width is 16 microns. .

Step 1: Clean the purchased commercial silicon substrate nitride epitaxial wafer once with acetone, absolute ethanol and deionized water, blow dry it with a nitrogen gun, and use a glue leveler to apply the glue on the front of the wafer (p-type gallium nitride). The upper surface of layer 5) is spin-coated with photoresist AZ5214 at a speed of 4000 rpm, and the spin-coating time is 40 seconds (photoresist thickness is 1.5 microns);

Using the photolithography process, the positive electrode disc and its supporting waveguide microcavity structure are defined on the spin-coated photoresist layer. The photolithography machine model is MA6.

Step 2: Use an electron beam evaporation process to evaporate 700nm metal nickel on the surface of the p-type gallium nitride layer 5, and then use an acetone solution to remove the remaining photoresist.

The third step: Use the III-V inductively coupled plasma etching process to etch down the nitride layer to the upper surface of the n-type gallium nitride layer, thereby converting the disk and waveguide structures defined in the first step. The pattern is transferred to the quantum well layer 4 and p-type gallium nitride layer 5 of the silicon-based nitride epitaxial wafer, and then the remaining metallic nickel on the wafer is removed with a dilute nitric acid solution.

Step 4: Use a glue leveling machine to spin-coat photoresist AZ5214 on the upper surface of the silicon-based nitride epitaxial wafer at a speed of 4000 rpm, and the spin-coating time is 50 seconds (photoresist thickness is 2 microns); then use The photoresist layer spin-coated by the photolithography process defines the pattern of the negative electrode disk and the waveguide microcavity structure it supports.

Step 5: Use electron beam evaporation process to evaporate 700nm metal nickel on the upper surface of the pattern structure. Finally, use acetone solution to remove the remaining photoresist and peel off the metal nickel.

Step 6: Use the ICP etching process to etch down the n-type gallium nitride layer along the complete waveguide structure defined above to the upper surface of the silicon substrate layer, thereby transferring the complete pattern structure downward to the n-type Gallium nitride layer 3 and U-type gallium nitride layer 2, and finally use dilute nitric acid solution to remove metallic nickel.

Step 7: Use a glue leveler to spin-coat photoresist AZ5214 on the front of the wafer at 4000 rpm. The spin-coating time is 50 seconds (photoresist thickness is 2 microns). Use photolithography technology. The left and right sides of the adhesive layer define the n-type area electrode pattern and the p-type area electrode pattern respectively. The photolithography machine model is MA6.

Step 8: Use an electron beam evaporation process to evaporate metal (Au/Ni) on the upper surface of the electrode pattern, so that p-type gallium nitride layer 5 and n-type gallium nitride layer 3 are plated with p-type electrodes 6 and n respectively. Type electrode 7, and finally use acetone solution to remove the remaining photoresist and peel off the excess Au/Ni.

Using an isotropic wet etching process to etch the silicon substrate layer 1 from the bottom of the waveguide microcavity, a suspended waveguide structure microcavity supported by silicon pillars can be obtained. The etching solution is a mixed solution of hydrofluoric acid and dilute nitric acid with a ratio of 1:1.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be used Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent substitutions are made to some or all of the technical features; however, these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims (7)

1. The electric pump nitride suspended waveguide micro-laser is characterized in that the laser takes a silicon-based nitride epitaxial wafer as a carrier and comprises a silicon substrate layer (1), a u-type gallium nitride layer (2), an n-type gallium nitride layer (3), a quantum well layer (4), a p-type gallium nitride layer (5), a p-type electrode (6) arranged on the p-type gallium nitride layer (5) and an n-type electrode (7) arranged on the upper surface of the n-type gallium nitride layer (3), wherein the u-type gallium nitride layer (2), the n-type gallium nitride layer (3), the quantum well layer (4) and the p-type gallium nitride layer (5) are sequentially arranged from bottom to top; the laser is provided with a waveguide microcavity structure comprising an anode disc microcavity and a cathode disc microcavity, the anode disc microcavity and the cathode disc microcavity are connected through a waveguide, and the lower parts of the anode disc microcavity and the cathode disc microcavity are respectively supported by a silicon substrate layer (1).

2. The electric pump nitride suspended waveguide micro-laser according to claim 1, wherein the positive electrode disc microcavity structure penetrates through the p-type gallium nitride layer (5) and the quantum well layer (4).

3. The electric pump nitride suspended waveguide micro-laser according to claim 1 or 2, wherein the p-type electrode (6), the p-type gallium nitride layer (5) and the quantum well layer (4) are arranged in a positive disc microcavity; the n-type electrode (7) and the n-type gallium nitride layer (3) are arranged in the negative disc microcavity.

4. The pump nitride suspended waveguide micro-laser of claim 1, wherein the positive disc microcavity and the negative disc microcavity are stepped.

5. An electric pump nitride suspended waveguide micro-laser according to claim 1, characterized in that the n-type electrode (7) is formed in the centre of the negative disc microcavity; the p-type electrode (6) is formed in the center of the anode disc microcavity.

6. A method of making the electric pump nitride suspended waveguide micro-laser of any one of claims 1-5, comprising:

the first step: spin-coating photoresist on the upper surface of a p-type gallium nitride layer (5) of a silicon-based nitride epitaxial wafer, and defining a graph of a positive disc microcavity on the spin-coated photoresist layer by adopting a photoetching process;

and a second step of: evaporating metallic nickel on the graph of the positive plate micro-cavity by adopting an electron beam evaporation process, and removing residual photoresist;

and a third step of: etching the nitride layer downwards by adopting an ICP etching process until the upper surface of the n-type gallium nitride layer (3) is reached, so that the pattern structure defined in the first step is downwards transferred into the p-type gallium nitride layer (5) and the quantum well layer (4) of the silicon-based nitride epitaxial wafer, and then dilute nitric acid is used for removing metallic nickel;

fourth step: spin-coating photoresist on the upper surface of the silicon-based nitride epitaxial wafer, and defining a pattern of a negative disc microcavity on the spin-coated photoresist layer by adopting a photoetching process;

fifth step: evaporating metallic nickel on the surface of the pattern structure of the negative disc microcavity by adopting an electron beam evaporation process, and removing residual photoresist;

sixth step: etching the n-type gallium nitride layer (3) downwards along the defined complete negative disc microcavity structure by adopting an ICP etching process until reaching the upper surface of the silicon substrate layer (1), thereby transferring the pattern structure of the complete negative disc microcavity to the n-type gallium nitride layer (3) and the u-type gallium nitride layer (2) in sequence, and finally removing metallic nickel by using dilute nitric acid;

seventh step: spin-coating photoresist on the upper surface of the silicon-based nitride epitaxial wafer, and defining a p-type region electrode pattern and an n-type region electrode pattern on the spin-coated photoresist layer by adopting a photoetching process;

eighth step: evaporating a positive electrode on the upper surface of the electrode pattern of the p-type region by adopting an electron beam evaporation process, evaporating a negative electrode on the upper surface of the electrode pattern of the n-type region, respectively plating positive and negative electrodes on the p-type gallium nitride layer (5) and the n-type gallium nitride layer (3), finally removing residual photoresist, and stripping Au/Ni on the photoresist to obtain a p-type electrode (6) and an n-type electrode (7);

ninth step: and etching the silicon substrate layer (1) by using an isotropic wet method, so that silicon columns supporting discs at two sides of the waveguide are formed in the silicon substrate layer (1), and a completely suspended waveguide microcavity is obtained.

7. The method of making an electric pump nitride suspended waveguide micro-laser of claim 6, wherein the positive and negative electrodes are both evaporated Au/Ni.