Laser and method for manufacturing the same

Abstract

The present invention relates to a laser and a method for preparing the same. The method for preparing the laser comprises: providing a silicon substrate; forming an active layer on the silicon substrate, wherein the active layer comprises a III-V group quantum dot material; forming an upper waveguide layer on the upper surface of the active layer; and forming a grating in the upper waveguide layer by using an equivalent chirp technique. The method for preparing the above-mentioned laser, by replacing the traditional quantum well active layer with a quantum dot active layer, makes full use of the characteristics of quantum dots being insensitive to dislocations, thereby improving the luminous efficiency of the laser; and, by using the equivalent chirp technique to form a grating in the waveguide layer, the manufacturing cost is reduced, the efficiency is improved, and the laser is suitable for low-cost large-scale manufacturing. In addition, the equivalent chirp technique can flexibly adjust the spacing between sub-gratings in the grating to achieve accurate selection of the wavelength, which is conducive to realizing multi-wavelength high integration of the laser.

Description

Technical Field

[0001] The invention relates to an optoelectronic device, in particular to a laser and a preparation method thereof. Background Art

[0002] Traditional high-speed lasers mostly use a distributed negative feedback design. In order to achieve precise phase conversion etching of the grating, the industry usually chooses electron beam exposure, which is very time-consuming and has limited yield. In addition, traditional high-speed lasers usually use a quantum well emission structure design on an indium phosphide substrate. However, the epitaxy cost of the indium phosphide substrate is high, and the wafer process yield is low; and the quantum well emission structure is very sensitive to dislocations, making it difficult to achieve silicon-based integration with high luminous efficiency. Summary of the invention

[0003] Based on this, it is necessary to provide a new laser and its preparation method to address the problems of time-consuming and dislocation-sensitive traditional distributed negative feedback laser preparation process.

[0004] A method for preparing a laser comprises: providing a silicon substrate; forming an active layer on the silicon substrate, wherein the active layer comprises a III-V group quantum dot material; forming an upper waveguide layer on the upper surface of the active layer; and forming a grating in the upper waveguide layer by using an equivalent chirp technique.

[0005] The above-mentioned laser preparation method replaces the traditional quantum well active layer with a quantum dot active layer, making full use of the characteristics of quantum dots being insensitive to dislocations to improve the luminous efficiency of the laser; and by using the equivalent chirp technology to form the grating in the waveguide layer, the manufacturing cost is reduced, the efficiency is improved, and it is suitable for low-cost large-scale manufacturing. In addition, the equivalent chirp technology can flexibly adjust the spacing of the sub-gratings in the grating, so that the prepared grating has extremely strong wavelength selectivity.

[0006] In one embodiment, before forming the active layer on the silicon substrate, the method further includes: sequentially epitaxially generating a buffer layer, a lower contact layer, a lower confinement layer and a lower waveguide layer on the upper surface of the silicon substrate; wherein the active layer is located on the upper surface of the lower waveguide layer. The buffer layer can further filter dislocations and reduce the influence of dislocations on luminous efficiency.

[0007] In one embodiment, a dislocation of a first angle is formed between the III-V group quantum dot material and the silicon substrate.

[0008] In one embodiment, the III-V group quantum dot material includes indium arsenide quantum dots.

[0009] In one embodiment, a plurality of lasers with different wavelengths are fabricated on the silicon substrate.

[0010] The present application also discloses a laser, comprising: a silicon substrate; an active layer located above the silicon substrate, the active layer comprising a III-V group quantum dot material; an upper waveguide layer located on the upper surface of the active layer, a grating formed in the upper waveguide layer; wherein the grating is formed using an equivalent chirp technology.

[0011] The laser uses III-V quantum dot materials to make the active layer for light emission, which can reduce the influence of dislocation on the light emission efficiency compared with the traditional quantum well active layer. In addition, the grating in the upper waveguide layer is made by equivalent chirp technology, which greatly reduces the preparation cost of the laser.

[0012] In one embodiment, the silicon substrate and the active layer further include: a buffer layer, a lower contact layer, a lower confinement layer and a lower waveguide layer stacked in sequence from bottom to top. The buffer layer can filter dislocations and reduce the impact of dislocations on luminous efficiency.

[0013] In one embodiment, the III-V group quantum dot material includes: Indium Arsenide quantum dots.

[0014] In one of the embodiments, there is a dislocation of a first angle between the III-V group quantum dot material and the silicon substrate.

[0015] A multi-wavelength array laser comprises a plurality of lasers as described in any one of the above embodiments, each laser having a different wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, drawings of other embodiments can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a flowchart of a method for preparing a laser in one embodiment of the present application.

[0018] Figure 2 Schematic diagram of the cross-sectional structure of a laser in one embodiment of the present application.

[0019] Figure 3 FIG. 1 is a schematic diagram of the cross-sectional structure of a laser in another embodiment of the present application.

[0020] Explanation of the accompanying drawings: 1. Silicon substrate; 2. Active layer; 3. Upper waveguide layer; 4. Buffer layer; 5. Lower contact layer; 6. Lower confinement layer; 7. Lower waveguide layer; 9. Upper confinement layer; 10. Upper contact layer; 11. N-type electrode; 12. P-type electrode. DETAILED DESCRIPTION

[0021] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0023] It should be understood that when an element or layer is referred to as "on ...", "adjacent to ...", "connected to" or "coupled to" other elements or layers, it can be directly on, adjacent to, connected to or coupled to other elements or layers, or there can be intervening elements or layers. On the contrary, when an element is referred to as "directly on ...", "directly adjacent to ...", "directly connected to" or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings of the present application, the first element, component, region, layer or part discussed below can be represented as a second element, component, region, layer or part.

[0024] Spatially relative terms such as "under," "below," "below," "under," "above," "above," etc., may be used herein for ease of description to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that in addition to the orientations shown in the figures, the spatially relative terms are intended to include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is flipped, then the elements or features described as "under other elements" or "under" or "under" will be oriented as "on" the other elements or features. Therefore, the exemplary terms "under" and "under" may include both upper and lower orientations. The device may be oriented otherwise (rotated 90 degrees or other orientations) and the spatial descriptors used herein are interpreted accordingly.

[0025] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0026] The laser in the present application may be a distributed negative feedback laser (DFB). Conventional distributed negative feedback lasers are usually based on quantum well schemes on indium phosphide substrates, and gratings are made through electron beam exposure process to achieve wavelength selection and narrow line width lasing. However, the indium phosphide substrates currently available in the industry are generally below 4 inches, and the production and epitaxy costs of indium phosphide substrates are very high. In addition, the yield of indium phosphide wafer process is low, and the production efficiency of electron beam exposure process is low, which cannot meet the preparation requirements of large-scale, multi-wavelength distributed negative feedback lasers.

[0027] In order to improve the above situation, an embodiment of the present application provides a method for preparing a laser, such as Figure 1 As shown, including:

[0028] S11: Provide a silicon substrate.

[0029] S12: forming an active layer on the silicon substrate, wherein the active layer comprises a III-V group quantum dot material.

[0030] S13: forming an upper waveguide layer on the upper surface of the active layer.

[0031] S14: forming a grating in the upper waveguide layer using an equivalent chirp technique.

[0032] In step S11, the size of silicon wafers currently available in the industry can reach 12 inches. Compared with indium phosphide substrates of less than 4 inches, producing lasers on larger silicon substrates can reduce manufacturing costs.

[0033] In step S12, silicon, as an indirect bandgap semiconductor material, is difficult to achieve effective luminescence, so a silicon-based light source can be obtained by integrating III-V group quantum dot materials. III-V group semiconductors, as direct bandgap materials, have extremely high luminescence efficiency. For example, III-V group quantum dot materials may include indium arsenide (InAs) quantum dots. Specifically, molecular beam epitaxy (MBE) technology can be used to form an active layer structure containing III-V group quantum dot materials on a silicon substrate. Among them, by means of the independent characteristics of quantum dots, even if there are individual dislocated quantum dots, it will not affect the optical properties of other quantum dots. The traditional quantum well active layer belongs to a two-dimensional quantum thin film material, which makes it easy for dislocations to derive and transmit in the thin film layer, reducing the luminescence efficiency.

[0034] In step S13, an upper waveguide layer is formed on the upper surface of the active layer. The upper waveguide layer is located above the active layer. Optionally, in other embodiments, a waveguide layer may also be provided below the active layer, and the waveguide layer located below the active layer may be referred to as a lower waveguide layer. By forming a grating, such as a Bragg grating, in the waveguide layer, light waves can obtain gain while being fed back, thereby enhancing the wavelength selectivity of the laser and improving the monochromaticity. The Bragg grating mainly causes Bragg reflection by controlling the periodic change of the refractive index, i.e., index coupling (Index-Coupling).

[0035] The quality of the Bragg grating directly affects the quality of the semiconductor laser and determines the quality of the semiconductor laser. However, due to the complex structure and high difficulty of the Bragg grating, it is often necessary to use a costly electron beam exposure process for preparation, which is difficult to apply to the manufacture of large-scale multi-wavelength distributed negative feedback lasers. Therefore, in step S14, the present application adopts another process to prepare the grating, which can not only ensure the grating quality, but also greatly reduce the preparation cost.

[0036] In step S14, based on the equivalent chirp technology, one holographic exposure and one micro-nanoscale lithography are used to etch the grating to prepare an equivalent grating. In the effective broadband of the equivalent grating, the equivalent grating can replace the Bragg grating to achieve the same optical response. The so-called equivalent grating can also be called a shadow grating. The Bragg grating has multiple reflection peaks, each reflection peak corresponds to a Fourier coefficient, and the Fourier coefficients of +1 and -1 correspond to the two reflection peaks closest to the central Bragg wavelength, respectively, and each reflection peak represents a shadow grating. Both the +1 and -1 shadow gratings can be selected as equivalent gratings.

[0037] As an example, a mask plate may be prepared first, and the mask plate has a desired sampling period distribution. For example, the sampling period of the mask plate may be 3 microns, and the duty cycle of each sampling period is 0.5. The sampling period is changed in the center of the mask plate, for example, from 3 microns to 2 microns. The sampling period of other parts remains unchanged at 3 microns. Then, the upper waveguide layer is holographically exposed based on the above mask plate, and finally etching, cleaning and other processes are performed to obtain the desired equivalent grating.

[0038] The equivalent chirp technology can achieve various nanoscale changes of gratings by using one holographic exposure and one ordinary micron-level lithography. It is suitable for low-cost and large-scale lithography of the gratings of multiple lasers, achieving precise control of the laser wavelength and obtaining lasers with different wavelengths.

[0039] The preparation method of the above laser combines silicon-based quantum dot technology with equivalent chirp technology, which not only reduces the impact of dislocations on the luminous efficiency of the laser, but also quickly and efficiently prepares equivalent gratings through equivalent chirp technology, reducing the preparation cost of the laser, improving efficiency and yield, and effectively solving the severe challenges of low production efficiency and high manufacturing cost of electron beam exposure in the current distributed negative feedback laser grating manufacturing process. Moreover, when the above method is applied to prepare silicon-based multi-wavelength distributed negative feedback lasers, thanks to the high production efficiency of lithography compared to electron beam exposure technology, the preparation method of the above laser can also achieve multi-wavelength high integration of silicon-based multi-wavelength distributed negative feedback lasers.

[0040] In one embodiment, before forming the active layer on the silicon substrate, it also includes: sequentially epitaxially generating a buffer layer, a lower contact layer, a lower confinement layer and a lower waveguide layer on the upper surface of the silicon substrate; wherein the active layer is located on the upper surface of the lower waveguide layer.

[0041] Specifically, the laser structure prepared by the method in this embodiment is as follows: Figure 2 As shown. For example, the buffer layer 4, the lower contact layer 5, the lower confinement layer 6 and the lower waveguide layer 7 can be sequentially formed by molecular beam epitaxy technology. Among them, the nucleation layer of aluminum arsenic is epitaxially grown on a beveled silicon substrate to control the penetration dislocation density, and the dislocation is further filtered by epitaxially growing a buffer layer 4 with a micron-level thickness, so that the dislocation penetrating into the active layer 2 is reduced. In addition, since the active layer 2 includes III-V quantum dot materials, such as indium arsenide quantum dots, and the quantum dots are insensitive to dislocations, the influence of dislocations on the luminous efficiency of the laser can be reduced.

[0042] For example, the lower contact layer 5 can be an N-type contact layer. The lower limiting layer 6 is mainly used to limit the leakage of light generated by the active area to form an optical limit. For example, the lower limiting layer 6 can be formed of a material with a higher refractive index than the waveguide layer. Optionally, an upper limiting layer is also formed above the active layer, and the upper limiting layer is made of the same material as the lower limiting layer.

[0043] The preparation of the lower waveguide layer 7 can refer to the upper waveguide layer 3. The two waveguide layers are the same and are both used to transmit the light generated in the active area.

[0044] In one embodiment, a dislocation of a first angle is formed between the III-V quantum dot material and the silicon substrate 1. As an example, the first angle may be 90 degrees, or an angle close to 90 degrees, such as 87 degrees, 89 degrees, 91 degrees, or 93 degrees. By forming a dislocation of 90 degrees or close to 90 degrees between the III-V quantum dot material and the silicon substrate 1, the problem of anti-phase domains between the silicon material and the III-V material is effectively overcome, and the quantum dot material is insensitive to dislocations, so that the influence of dislocations on luminous efficiency can be minimized.

[0045] In one embodiment, after forming a grating in the upper waveguide layer 3 using an equivalent chirp technique, the method further includes: forming an upper confinement layer 9 and an upper contact layer 10 on the upper waveguide layer 3, such as Figure 3 shown.

[0046] Specifically, the upper limiting layer 9 and the upper contact layer 10 can be prepared by using metal-organic chemical vapor deposition (MOCVD). MOCVD is a new type of vapor phase epitaxial growth technology developed on the basis of vapor phase epitaxy (VPE). MOCVD can use organic compounds of group III and group II elements and hydrides of group V and VI elements as crystal growth source materials, and perform vapor phase epitaxy on the substrate in a thermal decomposition reaction mode to grow various group III-V, group II-VI compound semiconductors and their multi-component solid solutions of thin-layer single crystal materials.

[0047] Further, a metal electrode may be sputtered on the surface of the upper contact layer 10 to form a P-type electrode 12. An N-type electrode 11 is formed on the lower surface of the silicon substrate 1, and power may be supplied to the laser through the P-type electrode 12 and the N-type electrode 11. For example, the upper contact layer 10 is a P-type contact layer, and the lower contact layer 5 is an N-type contact layer.

[0048] As an example, the lower contact layer 5 and the upper contact layer 10 may be III-V material layers, and the P-type electrode 12 and the N-type electrode 11 may be metal titanium, gold or other metal films.

[0049] In one embodiment, a plurality of lasers with different wavelengths are prepared on a silicon substrate 1 to form a multi-wavelength array laser. Specifically, the laser preparation method in the above embodiment can be used to prepare a plurality of lasers on a silicon substrate 1, different lasers have different wavelengths, and a plurality of laser arrays are arranged on a silicon substrate. For example, the waveguide process in silicon-based optoelectronics and the electric modulation technology of the electro-optical modulator can be used to realize silicon-based monolithic laser array integration. Since the equivalent chirp technology can equivalently realize various grating nanometer-level changes using one holographic exposure and one ordinary micron-level lithography, it has a strong control ability over the wavelength and is therefore very suitable for low-cost large-scale manufacturing. By combining the equivalent chirp technology with the silicon-based quantum dot laser technology, a multi-wavelength array laser can be prepared at low cost, which can greatly improve the production efficiency and reduce the cost compared with the electron beam exposure process. The multi-wavelength array laser prepared in this embodiment can be used in a wavelength division multiplexing system in high-speed optical communication to increase the information carrying capacity of the optical module. Therefore, the combination of a silicon-based quantum dot integrated laser and an equivalent chirp technology provides a method for preparing a wavelength division multiplexing laser.

[0050] For example, the preparation method of the laser in the above embodiment can be used to prepare a wavelength division multiplexing multi-wavelength long-wave 1310nm laser. The wavelength division multiplexing multi-wavelength long-wave 1310nm laser has a low threshold current and can achieve high-efficiency room temperature continuous lasing.

[0051] An embodiment of the present application also provides a laser, such as Figure 2 As shown, it includes: a silicon substrate 1; an active layer 2, located above the silicon substrate 1, and the active layer 2 includes a III-V group quantum dot material; an upper waveguide layer 3, located on the upper surface of the active layer 2, and a grating is formed in the upper waveguide layer 3; wherein the grating is formed by using an equivalent chirp technology.

[0052] Specifically, the III-V quantum dot material can be indium arsenide quantum dots. III-V semiconductors are direct bandgap materials with extremely high luminescence efficiency. In addition, since quantum dots have independent characteristics, even if there are individual quantum dots with dislocations, they will not affect the optical properties of other quantum dots. Since traditional high-resolution lasers usually adopt a quantum well edge emission structure design of an indium phosphide substrate, the active region is very sensitive to dislocations and the luminescence efficiency is severely limited. Therefore, the laser in this embodiment uses III-V quantum dot materials to make the active layer 2, which reduces the sensitivity of the active layer 2 to dislocations compared to the traditional quantum well active region, and the luminescence efficiency of the laser is significantly improved.

[0053] Furthermore, a grating is provided in the upper waveguide layer 3 located on the upper surface of the active layer 2, and the grating is prepared by an equivalent chirp technique. By using the equivalent chirp technique, an equivalent grating can be prepared using one holographic exposure and one micro-nanoscale lithography. In the effective broadband of the equivalent grating, the equivalent grating can replace the Bragg grating to achieve the same optical response. The equivalent chirp technique can prepare an equivalent grating quickly, efficiently and accurately. In the manufacture of large-scale multi-wavelength distributed negative feedback lasers, the equivalent chirp technique has the technical advantages of high yield and low cost.

[0054] The above laser includes a layer of III-V quantum dot material and a grating prepared by equivalent chirp technology. It is not only significantly better than the traditional quantum well laser in terms of luminous efficiency, but also, due to the use of a grating preparation technology with a higher yield, the quality of the laser is significantly better than the luminous quality brought by the grating prepared by electron beam exposure technology. For highly integrated multi-channel products, the laser in this application has great advantages.

[0055] In one embodiment, please continue to refer to Figure 2 , the silicon substrate 1 and the active layer 2 also include: a buffer layer 4, a lower contact layer 5, a lower limiting layer 6 and a lower waveguide layer 7 stacked from bottom to top. Among them, the buffer layer 4 can be used to filter dislocations, so that the dislocations penetrating into the active layer 2 are reduced. The lower limiting layer 6 is mainly used to limit the leakage of light generated in the active area to form an optical limit. For example, the lower limiting layer 6 can be formed of a material with a higher refractive index than the waveguide layer. The lower waveguide layer 7 is no different from the upper waveguide layer 3, and both are used to transmit the light generated in the active area.

[0056] In one embodiment, there is a dislocation of a first angle between the III-V group quantum dot material and the silicon substrate 1. As an example, the first angle may be 90 degrees, or an angle close to 90 degrees, such as 87 degrees, 89 degrees, 91 degrees, or 93 degrees. By setting the dislocation angle between the III-V group quantum dot material and the silicon substrate 1 to a right angle or an angle close to a right angle, the effect of the dislocation on the luminous efficiency can be minimized.

[0057] In one embodiment, Figure 3 As shown, the laser further includes an upper confinement layer 9 and an upper contact layer 10. As an example, the upper contact layer 10 is a P-type contact layer, and a P-type electrode 12 is disposed on the upper surface of the upper contact layer 10; the lower contact layer 5 is an N-type contact layer, and an N-type electrode 11 is disposed on the lower surface of the silicon substrate 1. The P-type electrode 12 and the N-type electrode 11 can be titanium thin films, gold thin films or other metal thin films.

[0058] A multi-wavelength array laser includes a plurality of lasers described in any of the above embodiments, each laser having a different wavelength. The plurality of laser arrays are arranged on the same substrate. The multi-wavelength array laser can be used in a wavelength division multiplexing system in high-speed optical communication, which can greatly improve the information carrying capacity of an optical module.

[0059] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a laser, characterized in that: include: providing a silicon substrate; forming an active layer on the silicon substrate, wherein the active layer comprises a III-V group quantum dot material; forming an upper waveguide layer on the upper surface of the active layer; An equivalent chirp technique is used to form a grating in the upper waveguide layer.

2. The method for preparing a laser according to claim 1, characterized in that: Before forming an active layer on the silicon substrate, the method further comprises: Epitaxially generating a buffer layer, a lower contact layer, a lower confinement layer and a lower waveguide layer in sequence on the upper surface of the silicon substrate; Wherein, the active layer is located on the upper surface of the lower waveguide layer.

3. The method for preparing a laser according to claim 1, characterized in that: A dislocation of a first angle is formed between the III-V group quantum dot material and the silicon substrate, wherein the first angle is any one of 87 degrees, 89 degrees, 90 degrees, 91 degrees or 93 degrees.

4. The method for preparing a laser according to claim 1, characterized in that: The III-V group quantum dot material includes: indium arsenide quantum dots.

5. The method for preparing a laser according to any one of claims 1 to 4, characterized in that: A plurality of lasers with different wavelengths are prepared on the silicon substrate to form a multi-wavelength array laser.

6. A laser, characterized in that: include: Silicon substrate; An active layer, located above the silicon substrate, wherein the active layer comprises a III-V group quantum dot material; an upper waveguide layer, located on the upper surface of the active layer; A grating is formed in the upper waveguide layer; wherein the grating is formed by using an equivalent chirp technology.

7. The laser according to claim 6, characterized in that The silicon substrate and the active layer further include: a buffer layer, a lower contact layer, a lower confinement layer and a lower waveguide layer stacked in sequence from bottom to top.

8. The laser according to claim 6, characterized in that The III-V group quantum dot material includes: indium arsenide quantum dots.

9. The laser according to claim 6, characterized in that There is a dislocation of a first angle between the III-V group quantum dot material and the silicon substrate, wherein the first angle is any one of 87 degrees, 89 degrees, 90 degrees, 91 degrees or 93 degrees.

10. A multi-wavelength array laser, comprising a plurality of lasers according to any one of claims 6 to 9, characterized in that: Each laser has a different wavelength.

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