Laser structure and preparation method

Abstract

The invention discloses a laser structure and a preparation method. The laser structure comprises a semiconductor function layer arranged on the surface of a substrate; the surface of the semiconductor function layer is provided with a latticed structure, the latticed structure penetrates through the semiconductor function layer and is communicated with a cavity arranged on the surface of the substrate below the latticed structure, so that the latticed structure is suspended on the cavity, and the width of a latticed framework of the latticed structure is gradually reduced from the edge to the middle. According to the laser structure, the electroluminescence effect can be remarkably enhanced, and therefore the problems that due to the indirect band gap structure of germanium, the transmitting power and efficiency of a traditional silicon-based germanium laser are limited, and the threshold current is high can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular, to a laser structure and a preparation method thereof. Background Art

[0002] In traditional silicon-based germanium lasers, due to the indirect bandgap structure of germanium, the emission power and efficiency of the lasers are limited, and the problem of high threshold current of the devices is caused. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and to provide a laser structure and a preparation method thereof.

[0004] To achieve the above purpose, the technical solution of the present invention is as follows:

[0005] The present invention provides a laser structure, including:

[0006] A semiconductor functional layer disposed on the surface of a substrate;

[0007] A grid-like structure is disposed on the surface of the semiconductor functional layer, the grid-like structure penetrates through the semiconductor functional layer and is connected to a cavity disposed on the surface of the lower substrate, so that the grid-like structure is suspended on the cavity, and the grid framework of the grid-like structure has a width that gradually decreases from the edge to the middle.

[0008] Further, a two-dimensional material layer is disposed on the surface of the semiconductor functional layer, the two-dimensional material layer is at least stacked on the surface of the grid-like structure facing away from the cavity, and the two-dimensional material layer and the semiconductor functional layer form a vertical pn junction facing the substrate to inject carriers.

[0009] Further, the semiconductor functional layer includes a germanium thin film layer; and / or, the two-dimensional material layer includes a graphene thin film layer or a germanene thin film layer; and / or, the two-dimensional material layer at the grid-like structure conforms to the semiconductor functional layer.

[0010] Further, it further includes: an optical reflection structure, and the optical reflection structure includes two gratings respectively disposed on the surfaces of the semiconductor functional layer outside the opposite sides of the grid-like structure.

[0011] Further, the grid-like structure has a plurality of grids formed by the grid frameworks arranged in a cross direction, the two gratings are distributed in an arc shape, and are disposed outside the two ends of the grid framework in the same direction in a manner that the arc concave surfaces face each other.

[0012] The present invention also provides a method for preparing a laser structure, including:

[0013] Providing a substrate;

[0014] Form a semiconductor functional layer on the surface of the substrate;

[0015] Form a through grid-like structure on the surface of the semiconductor functional layer, and make the grid framework of the grid-like structure have a width that gradually narrows from the edge to the middle;

[0016] Form a cavity communicating with the grid-like structure on the surface of the substrate below the grid-like structure, so that the grid-like structure is suspended on the cavity.

[0017] Further, when forming the semiconductor functional layer, it further includes: performing n-type in-situ doping on the semiconductor functional layer to form the n-type semiconductor functional layer; after forming the n-type semiconductor functional layer, it further includes: forming a two-dimensional material layer on the surface of the semiconductor functional layer, so that the two-dimensional material layer and the n-type semiconductor functional layer form a vertical pn junction facing the substrate for injecting carriers; when forming the grid-like structure and the cavity, first use photolithography and dry etching processes to pattern the two-dimensional material layer and the semiconductor functional layer simultaneously, form a through and conformal grid-like structure on the two-dimensional material layer and the semiconductor functional layer, and make the grid framework have a width that gradually narrows from the edge to the middle, and then use a wet etching process and use the mesh holes of the grid-like structure as a window to form a cavity communicating with the grid-like structure on the surface of the substrate below the grid-like structure, so that the grid-like structure is suspended on the cavity.

[0018] Further, after forming the cavity, it further includes: forming two gratings on the surfaces of the semiconductor functional layer outside the opposite sides of the grid-like structure to form a light reflection structure.

[0019] Further, when forming the grid-like structure, make the grid-like structure have a plurality of grids composed of the grid frameworks arranged in a cross direction; when forming the gratings, make the two gratings be distributed in an arc shape and be arranged on the outer sides of both ends of the grid framework in the same direction with the arc concave surfaces facing each other.

[0020] Further, use an epitaxial process and perform n-type in-situ doping simultaneously to form a germanium thin film layer as the semiconductor functional layer; use a chemical vapor deposition process to form a single-layer to multi-layer graphene thin film layer or germanene thin film layer as the two-dimensional material layer on the surface of the germanium thin film layer; when performing photolithography to pattern the two-dimensional material layer and the semiconductor functional layer simultaneously, first form an adhesion promoter on the surface of the graphene thin film layer or the germanene thin film layer, and then form a photoresist on the adhesion promoter to enhance the adhesion between the photoresist and the surface of the graphene thin film layer or the germanene thin film layer.

[0021] As can be seen from the above technical solution, the present invention proposes a novel laser structure. By forming a grid-like structure on a cavity suspended on the surface of a substrate on a semiconductor functional layer, and making the width of the grid framework gradually decrease from the edge to the middle, the suspension effect can be utilized to cause the semiconductor functional layer material located outside the grid-like structure to apply tensile stress to the semiconductor functional layer material located on the grid framework, and the semiconductor functional layer material on the grid framework can correspondingly generate tensile strain concentrated towards the middle. Taking the semiconductor functional layer made of n-type doped germanium material as an example, the energy difference between the indirect bandgap and the direct bandgap of germanium can be reduced by using the tensile strain concentrated in the middle of the grid framework, and the quasi-Fermi level of the conduction band of germanium can be made closer to the direct bandgap valley by using n-type doping, so that germanium exhibits the characteristics of a quasi-direct bandgap, and further, electron-hole pairs can achieve effective radiative recombination near the Brillouin zone. Further, by arranging a two-dimensional material layer and the semiconductor functional layer to form a vertical pn junction structure, a pump source using electrical injection of carriers can be formed, thereby realizing population inversion; by arranging a grating with an arc distribution, optical feedback can be provided in the suspended grid-like structure, thereby forming oscillation amplification and finally generating laser light. Therefore, the laser structure of the present invention can significantly enhance the electroluminescence effect, thereby effectively solving the problems that the traditional silicon-based germanium laser is limited by the indirect bandgap structure of germanium, restricting the emission power and efficiency of the laser, and having a high threshold current. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a top view of a laser structure according to a preferred embodiment of the present invention.

[0023] Figure 2 is Figure 1 a cross-sectional view taken along line A-A in

[0024] Figures 3 - 8 It is a schematic diagram of the process steps of a method for preparing a laser structure according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains. The words such as "including" used herein mean that the elements or objects appearing before this word cover the elements or objects enumerated after this word and their equivalents, without excluding other elements or objects.

[0026] To solve the problems in traditional silicon-based germanium lasers that, due to the indirect bandgap structure of germanium, the emission power and efficiency of the lasers are limited, and the threshold current of the devices is relatively high, the present invention provides a novel laser structure and a preparation method thereof.

[0027] Among them, the laser structure includes:

[0028] A semiconductor functional layer disposed on the surface of a substrate;

[0029] A grid-like structure is disposed on the surface of the semiconductor functional layer. The grid-like structure penetrates the semiconductor functional layer and is connected to a cavity disposed on the surface of the substrate below, so that the grid-like structure is suspended above the cavity. The grid framework of the grid-like structure has a width that gradually decreases from the edge to the middle.

[0030] The preparation method of the laser structure includes:

[0031] Provide a substrate;

[0032] Form a semiconductor functional layer on the surface of the substrate;

[0033] Form a through grid-like structure on the surface of the semiconductor functional layer, and make the grid framework of the grid-like structure have a width that gradually decreases from the edge to the middle;

[0034] Form a cavity connecting the grid-like structure on the surface of the substrate below the grid-like structure, so that the grid-like structure is suspended above the cavity.

[0035] In the present invention, a grid-like structure is formed on a cavity suspended on the surface of a substrate over a semiconductor functional layer, and the grid framework has a width that gradually decreases from the edge to the middle. By utilizing the suspension effect, the semiconductor functional layer material located outside the grid-like structure can apply a tensile stress to the semiconductor functional layer material located on the grid framework, and the semiconductor functional layer material on the grid framework can correspondingly generate a tensile strain that concentrates towards the middle. Applying the laser structure of the present invention can significantly enhance the electroluminescence effect, thereby effectively solving the problems of traditional silicon-based germanium lasers. Due to the indirect bandgap structure of germanium, the emission power and efficiency of the laser are limited, and the threshold current is relatively high.

[0036] Taking the germanium thin film layer as the semiconductor functional layer as an example, and in combination with the accompanying drawings, a further detailed description of a specific embodiment of a laser structure of the present invention will be given below.

[0037] Reference Figures 1 - 2 A laser structure of the present invention includes a germanium thin film layer 11 provided on the surface of a substrate 10 as a semiconductor functional layer. The germanium thin film layer 11 serves as the gain medium for forming the laser structure.

[0038] Among them, a grid-like structure 12 is provided on the surface of the germanium thin film layer 11. A cavity 15 is correspondingly provided on the surface of the substrate 10 below the grid-like structure 12, and the cavity 15 forms an opening opposite to the grid-like structure 12 on the surface of the substrate 10. The grid-like structure 12 penetrates through the germanium thin film layer 11 and is connected to the lower cavity 15 through the mesh holes 122 on the grid-like structure 12, so that the grid-like structure 12 is suspended on the cavity 15. The germanium thin film layer 11 material on the grid framework 121 of the grid-like structure 12 and the germanium thin film layer 11 material outside the boundary of the grid-like structure 12 are connected as a whole at the boundary of the grid-like structure 12.

[0039] The grid framework 121 has a width that gradually decreases from the edge (the boundary of the grid-like structure 12) to the middle 123 (the middle 123 of the grid-like structure 12). In this way, after the grid-like structure 12 loses the constraint effect generated by the substrate 10 on it due to being suspended on the cavity 15, the tensile force effect brought by the suspension can be utilized to prompt the germanium thin film layer 11 material located outside the grid-like structure 12 (outside the boundary) to apply a tensile stress to the germanium thin film layer 11 material located on the grid framework 121, and the germanium thin film layer 11 material on the grid framework 121 can correspondingly generate a tensile strain that concentrates towards the middle 123 due to the gradually decreasing width.

[0040] In some embodiments, the grid framework 121 in the middle 123 region has a relatively consistent width, which corresponds to the width of the grid framework 121 with a gradually decreasing width at the boundary of the middle 123.

[0041] Furthermore, the germanium thin film layer 11 includes a germanium thin film layer 11 doped with n-type dopants. On the one hand, by utilizing the tensile strain concentrated on the middle part 123 of the grid framework of the germanium thin film layer 11, the energy difference between the indirect bandgap and the direct bandgap of germanium can be reduced; at the same time, by heavily doping the germanium thin film layer 11 with n-type dopants, the quasi-Fermi level of the conduction band of germanium can be made closer to the direct bandgap valley, so that germanium exhibits the characteristics of a quasi-direct bandgap, and thus electron-hole pairs can achieve effective radiative recombination near the Brillouin zone. Therefore, the above structural characteristics can be utilized to reduce the threshold current of the germanium laser and achieve a narrow linewidth.

[0042] Reference Figures 1 - 2 。In some embodiments, a two-dimensional material layer 13 is further provided on the surface of the n-type doped germanium thin film layer 11. The two-dimensional material layer 13 is at least stacked on the surface of the grid-like structure 12 facing away from the cavity 15. For example, the two-dimensional material layer 13 can be stacked on the surface of the grid-like structure 12 and extend to the surface of a part of the germanium thin film layer 11 outside the boundary of the grid-like structure 12, so that the surface of the germanium thin film layer 11 at a position outside the two-dimensional material layer 13 is exposed. The two-dimensional material layer 13 is used to form a vertical pn junction facing the substrate 10 with the n-type doped germanium thin film layer 11, so as to realize a pump source for injecting carriers electrically, and thus achieve population inversion.

[0043] In some embodiments, the two-dimensional material layer 13 at the grid-like structure 12 is conformal with the germanium thin film layer 11. That is, the two-dimensional material layer 13 has the same grid-like structure 12 as the germanium thin film layer 11 above the cavity 15.

[0044] In some embodiments, the two-dimensional material layer 13 includes a graphene thin film layer 131 or a germanene thin film layer.

[0045] The substrate 10 may include a SOI substrate 10 to form a silicon-based tensile strain germanium laser structure.

[0046] Reference Figures 1 - 2 。In some embodiments, the laser structure further includes an optical reflection structure 14.

[0047] The optical reflection structure 14 includes two gratings 141 respectively disposed outside the opposite sides of the grid-like structure 12 (cavity 15) and on the exposed surface of the germanium thin film layer 11 outside the two-dimensional material layer 13.

[0048] In some embodiments, the grid-like structure 12 of the germanium thin film layer 11 has a plurality of grids formed by grid skeletons 121 arranged in a cross-cross direction. For example Figure 1A plurality of grids formed by a plurality of grid skeletons 121 arranged horizontally and vertically intersecting, thereby forming a micro-cross suspension bridge structure above the cavity 15. The middle (the middle part 123) of the micro-cross suspension bridge structure has a narrow bridge deck, and the two sides (the area between the middle part 123 and the boundary of the grid-like structure 12) have a wide bridge deck. After the substrate 10 is hollowed out to form the cavity 15, the germanium thin film layers 11 in the form of flat plates on the opposite sides of the micro-cross suspension bridge structure will generate biaxial (the horizontal axis and the vertical axis formed by the grid skeletons 121) tensile stress on the micro-bridge, which can concentrate the strain in the narrow suspended area of the bridge deck. Using this method, a large biaxial tensile strain has been successfully introduced into the germanium thin film layer 11 material.

[0049] The number of grid skeletons 121 in the horizontal direction and the number of grid skeletons 121 in the vertical direction may be the same or different.

[0050] The boundary of the grid-like structure 12 encloses a rectangle. Alternatively, the boundary of the grid-like structure 12 may also enclose other shapes, such as a circle, an ellipse, or a polygon with more than five sides, as well as irregular shapes.

[0051] Two gratings 141 are distributed in an arc to form a grating 141 with an arc structure. And, the two arc gratings 141 are respectively arranged on the outer sides of both ends of the grid skeletons 121 in the same direction with their arc concave surfaces facing each other. In this embodiment, the two arc gratings 141 are arranged on Figure 1 the outer sides of both ends of the grid skeletons 121 in the horizontal direction.

[0052] The pump source, the gain medium, and the optical resonator are the three major elements of a laser. In order to further reduce the threshold current of the silicon-based germanium laser and achieve a narrow linewidth, while introducing tensile strain into germanium, it is necessary to reasonably optimize the structural relationship among the three. Therefore, how to fabricate a germanium laser with a low threshold current based on the energy band engineering theory combined with the actual process is crucial.

[0053] Two-dimensional materials are a group of materials with a layered structure of several atomic thicknesses. Among them, graphene, as the most representative two-dimensional material, has unique structural, electrical, thermal, mechanical, and chemical properties, and has thus become one of the popular research fields for various applications in academia and industry. For example, the theoretical prediction of the electron mobility of graphene is 3×10 7 cm 2 / Vs, and the electron mobility of the graphene thin film grown by chemical vapor deposition (CVD) reported in experiments is 350000 cm 2 / Vs. The research on integrating two-dimensional materials into silicon-based germanium light sources can not only meet the requirements of electronic devices but also be of great significance for promoting the development of nano-scale silicon-based germanium lasers.

[0054] By designing the above-mentioned suspended grid-like structure 12 in the germanium thin film layer 11, the present invention successfully introduces a large biaxial tensile strain into the germanium material; at the same time, by forming a vertical pn junction between the two-dimensional material and germanium, a pump source optimization structure using electrical injection of carriers is realized; further, by arranging the arc-shaped distributed gratings 141, an arc-shaped distributed Bragg reflector structure (light reflection structure 14) is formed, and an arc-shaped optical resonator is formed between the two arc-shaped gratings 141, which can confine the light field in the distribution direction of the two arc-shaped gratings 141 and provide optical feedback in the suspended grid-like structure 12, thereby forming oscillation amplification and finally generating laser light. Therefore, the above-mentioned laser structure of the present invention has a significant enhancement effect on the electroluminescence of the laser, thus providing a new idea and approach for realizing a low-threshold current and narrow linewidth tensile strain germanium laser.

[0055] The following further details a method for preparing a laser structure of the present invention through specific embodiments and in conjunction with the accompanying drawings.

[0056] Refer to Figures 3 - 8 . A method for preparing a laser structure of the present invention can be used to prepare, for example, Figures 1 - 2 a laser structure of the present invention as shown above, and includes the following steps:

[0057] Step S1: Provide a substrate 10.

[0058] As Figure 3 shown, an SOI substrate 10 is used to further form a laser structure of the present invention on the SOI substrate 10.

[0059] In some embodiments, a cleaning treatment method is adopted to remove organic pollutants and metal ion contamination on the surface of the SOI substrate 10, and to remove the natural oxide film on the silicon surface of the SOI substrate 10.

[0060] Step S2: Sequentially form a germanium thin film layer 11 and a two-dimensional material layer 13 on the surface of the substrate 10.

[0061] As Figure 4 shown, an epitaxial process is used to form a germanium thin film layer 11 on the surface of the SOI substrate 10.

[0062] In some embodiments, a two-step deposition method of low temperature and high temperature and cyclic annealing are adopted to epitaxially grow a single-crystalline germanium thin film layer 11 on the surface of the SOI substrate 10. And while epitaxially growing the single-crystalline germanium thin film layer 11, n-type in-situ doping is carried out to form an n-type doped germanium thin film layer 11 as a semiconductor functional layer. Performing n-type doping on the germanium thin film layer 11 can improve the radiation efficiency of the germanium thin film layer 11 as a gain medium and further improve the light-emitting efficiency. In this embodiment, for example, AsH3 and PH3 are used as dopants to simultaneously perform n-type in-situ doping on the germanium thin film layer 11 during epitaxy.

[0063] After that, a chemical mechanical polishing (CMP) process is adopted to planarize the surface of the grown germanium thin film layer 11 to remove the uneven parts on the surface of the germanium thin film layer 11.

[0064] As Figure 5 shown, then, a two-dimensional material layer 13 is formed on the surface of the germanium thin film layer 11.

[0065] Taking the formation of a graphene thin film layer 131 as the two-dimensional material layer 13 on the surface of the germanium thin film layer 11 as an example, in some embodiments, a chemical vapor deposition (CVD) process is adopted to form a single-layer to multi-layer graphene thin film on the surface of the germanium thin film layer 11 to obtain a wafer-level graphene thin film layer 131. In this embodiment, a chemical vapor deposition method of metal-catalyzed graphene is adopted. By introducing a carbon source gas (precursor), such as methane gas, into the surface of the epitaxial germanium thin film layer 11 heated at high temperature, using the catalytic mechanism of germanium metal on methane gas, the methane gas is decomposed, resulting in the cleavage of carbon-hydrogen bonds and generating independently moving carbon atoms, that is, dehydrogenation reaction occurs. After the free carbon atoms adsorb and penetrate into the germanium surface and interior in a high-temperature gas atmosphere, they aggregate with each other to form new carbon-carbon bonds and cluster together, and then gradually grow. After cooling, a single-layer to several-layer graphene thin film layer 131 is formed on the germanium surface.

[0066] By forming the graphene thin film layer 131 on the surface of the germanium thin film layer 11, the graphene thin film layer 131 and the n-type germanium thin film layer 11 can form a vertical pn junction facing the SOI substrate 10 for electrical injection of carriers.

[0067] In some embodiments, in order to make the graphene thin film layer 131 have p-type characteristics to form a vertical pn junction with the germanium thin film layer 11 having n-type characteristics, the characteristics of the graphene thin film layer 131 can be changed by chemical doping of the graphene thin film layer 131. For example, a B (boron) substitution doping method can be adopted to make the graphene thin film layer 131 have p-type characteristics.

[0068] Alternatively, the doping by adsorption method can be adopted, in which dopants adsorbed on the surface of the graphene thin film layer 131 interact with the surface of the graphene thin film layer 131 to endow the graphene thin film layer 131 with p-type characteristics. Some organic molecules with electron groups can be used as dopants, such as NO2, tetracyanoethylene (TCNE), etc.

[0069] Or, an external negative voltage can be applied to adjust the Fermi level of graphene to be below the Dirac point to open the energy gap of graphene, which can also endow the graphene thin film layer 131 with p-type characteristics.

[0070] Step S3: A penetrating grid-like structure 12 is formed on the surfaces of the germanium thin film layer 11 and the two-dimensional material layer 13, and the grid skeleton 121 of the grid-like structure 12 has a width that gradually decreases from the edge to the middle 123.

[0071] First, the photolithography pattern of the grid-like structure (micro-cross suspension bridge) is defined by photolithography. Before spin-coating the photoresist on the surface of the graphene thin film layer 131, in order to enhance the adhesion between the photoresist and the surface of the graphene thin film layer 131 material, a tackifier is first formed on the surface of the graphene thin film layer 131, and then the photoresist is formed on the tackifier. In this embodiment, a layer of hexamethyldisilazane (HDMS) is spin-coated on the surface of the graphene thin film layer 131 as the tackifier, and then a photoresist layer is formed on the hexamethyldisilazane layer. When coating the photoresist, in order to control the surface uniformity of the photoresist without generating bubbles, a spin coater is used, and the initial rotation is at a slow speed (for example, the rotation speed is 450 - 550 rpm / min, preferably 500 rpm / min), and then at a high speed (for example, the rotation speed is 2500 - 3500 rpm / min, preferably 3000 rpm / min) to spin-coat the photoresist on the hexamethyldisilazane layer, and after soft baking, the photoresist is exposed.

[0072] As Figure 6 shown, then, a dry etching process is adopted to pattern the graphene thin film layer 131 and the germanium thin film layer 11 simultaneously, and a penetrating and conformal grid-like structure 12 is formed on the graphene thin film layer 131 and the germanium thin film layer 11, and the grid skeleton 121 has a width that gradually decreases from the edge to the middle 123 (refer to Figure 1 ).

[0073] In this embodiment, NF3 gas is used as the dry etching gas, and inductively coupled plasma (ICP) etching technology with high selectivity and directionality is selected to etch the graphene thin film layer 131 and the germanium thin film layer 11 after lithography, and a micro-cross suspended bridge structure (grid-like structure 12) with a depth slightly greater than the thickness of the germanium thin film layer 11 is etched out as the etching window for subsequent wet etching. During this step of etching, it is necessary to make the width of the grid framework 121 gradually decrease from the edge to the middle 123, and at this time, a relatively small initial tensile strain can be obtained. After etching, a grid-like structure 12 with multiple grids composed of multiple grid frameworks 121 arranged in a crosswise manner is obtained (refer to Figure 1 ).

[0074] By using the inductively coupled plasma etching method, not only can better etching directionality be obtained, but also the etching speed has been greatly improved. Thus, sidewalls of the grid-like structure 12 with high steepness in depth, uniform width, and smoothness can be formed.

[0075] Step S4: A cavity 15 communicating with the grid-like structure 12 is formed on the surface of the substrate 10 below the grid-like structure 12, so that the grid-like structure 12 is suspended above the cavity 15.

[0076] As Figure 7 shown, then, a wet etching process is adopted, and with the mesh holes 122 of the grid-like structure 12 as the etching window, a cavity 15 communicating with the grid-like structure 12 is formed on the surface of the SOI substrate 10 below the grid-like structure 12, so that the entire grid-like structure 12 is suspended above the opening of the cavity 15.

[0077] In this embodiment, a solution of tetramethylammonium hydroxide (TMAH) with a concentration of 4 - 8%, preferably about 5% concentration, is used to etch the silicon on the SOI substrate 10 below the germanium thin film layer 11. After the germanium thin film layer 11 material at the grid-like structure 12 loses the constraint of the substrate 10, due to the characteristic that the width of the grid framework 121 gradually shrinks from the edge to the middle 123, the germanium thin film layer 11 material outside the grid-like structure 12 will exert a biaxial tensile effect on the middle 123 region of the micro-cross suspended bridge structure, causing the initial tensile strain of the germanium thin film layer 11 material at the middle 123 of the grid-like structure 12 to redistribute, so that the strain is concentrated in the middle 123 region where the width of the grid framework 121 is narrower, promoting the germanium in the germanium thin film layer 11 to exhibit the characteristics of a quasi-direct bandgap.

[0078] Step S5: A light reflection structure 14 is formed on the surface of the germanium thin film layer 11 outside the grid-like structure 12.

[0079] As Figure 8As shown, then, through photolithography and etching processes, two oppositely arranged gratings 141 are formed on the surfaces of the germanium thin film layers 11 outside the opposite sides of the grid-like structure 12 to form a light reflection structure 14.

[0080] In this embodiment, photolithography and etching processes are used for patterning, such that the two formed gratings 141 are distributed in an arc shape and are arranged in an arc concave surface facing each other manner on the outer sides of both ends of the grid framework 121 in the same direction (shown as the horizontal direction in the figure). Thus, the grating 141 structure of the arc-distributed Bragg reflector is formed.

[0081] Metal electrode leads can also be further fabricated on the p-type graphene thin film layer 131 and the n-type germanium thin film layer 11 to pads. For example, Au, Ti, Al, etc. can be used as the metal electrode materials, and metal electrodes can be formed by using, for example, the TSV process in the traditional CMOS process. However, the present invention is not limited thereto.

[0082] In summary, the silicon-based biaxially tensile strained germanium laser structure of the present invention can significantly enhance the electroluminescence effect, thereby reducing the threshold current, and provides a new idea and approach for realizing a tensile strained germanium laser with a low threshold current and a narrow linewidth.

[0083] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes all fall within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A laser structure, characterized in that, Comprising: A semiconductor functional layer disposed on the surface of a substrate; A grid-like structure is provided on the surface of the semiconductor functional layer. The grid-like structure penetrates the semiconductor functional layer and is connected to a cavity provided on the surface of the substrate below, so that the grid-like structure is suspended above the cavity. The grid framework of the grid-like structure has a width that gradually decreases from the edge to the middle.

2. The laser structure according to claim 1, characterized in that, A two-dimensional material layer is provided on the surface of the semiconductor functional layer. The two-dimensional material layer is at least stacked on the surface of the grid-like structure facing away from the cavity. The two-dimensional material layer and the semiconductor functional layer form a vertical pn junction facing the substrate to inject carriers.

3. The laser structure according to claim 2, wherein, The semiconductor functional layer includes a germanium thin film layer; and / or, the two-dimensional material layer includes a graphene thin film layer or a germanene thin film layer; and / or, the two-dimensional material layer at the grid-like structure conforms to the semiconductor functional layer.

4. The laser structure according to claim 1, wherein Further comprising: A light reflection structure, which includes two gratings respectively disposed on the surfaces of the semiconductor functional layer outside the opposite sides of the grid-like structure.

5. The laser structure according to claim 4, wherein The grid-like structure has a plurality of grids formed by the grid frameworks arranged in a cross direction. The two gratings are distributed in an arc shape and are disposed on the outer sides of both ends of the grid frameworks in the same direction with the arc concave surfaces facing each other.

6. A method for preparing a laser structure, characterized in that, Comprising: Providing a substrate; Forming a semiconductor functional layer on the surface of the substrate; Forming a through grid-like structure on the surface of the semiconductor functional layer, and making the grid framework of the grid-like structure have a width that gradually decreases from the edge to the middle; Forming a cavity communicating with the grid-like structure on the surface of the substrate below the grid-like structure, so that the grid-like structure is suspended above the cavity.

7. The method for preparing the laser structure according to claim 6, characterized in that, When forming the semiconductor functional layer, it further includes: performing n-type in-situ doping on the semiconductor functional layer to form the n-type semiconductor functional layer; after forming the n-type semiconductor functional layer, it further includes: forming a two-dimensional material layer on the surface of the semiconductor functional layer, so that the two-dimensional material layer and the n-type semiconductor functional layer form a vertical pn junction facing the substrate for injecting carriers; when forming the grid-like structure and the cavity, first use photolithography and dry etching processes to pattern the two-dimensional material layer and the semiconductor functional layer simultaneously, form a through and conformal grid-like structure on the two-dimensional material layer and the semiconductor functional layer, and make the grid framework have a width that gradually decreases from the edge to the middle, and then use a wet etching process and take the mesh holes of the grid-like structure as windows to form a cavity communicating with the grid-like structure on the surface of the substrate below the grid-like structure, so that the grid-like structure is suspended above the cavity.

8. The method for preparing the laser structure according to claim 6, characterized in that, After forming the cavity, it further includes: forming two gratings on the surfaces of the semiconductor functional layer outside the opposite sides of the grid-like structure to form a light reflection structure.

9. The method for preparing the laser structure according to claim 8, wherein When forming the grid-like structure, the grid-like structure is made to have a plurality of grids formed by the grid skeletons arranged in a cross direction; when forming the grating, the two gratings are arranged in an arc distribution and are provided on the outer sides of both ends of the grid skeletons in the same direction with the concave surfaces of the arcs facing each other.

10. The method for preparing the laser structure according to claim 7, wherein An epitaxial process is adopted, and n-type in-situ doping is carried out simultaneously to form a germanium thin film layer as the semiconductor functional layer; a chemical vapor deposition process is adopted to form a monolayer to multilayer graphene thin film layer or a germanene thin film layer as the two-dimensional material layer on the surface of the germanium thin film layer; when performing a patterning photolithography process on the two-dimensional material layer and the semiconductor functional layer simultaneously, a tackifier is first formed on the surface of the graphene thin film layer or the germanene thin film layer, and then a photoresist is formed on the tackifier to enhance the adhesion between the photoresist and the surface of the graphene thin film layer or the germanene thin film layer.

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