Laser structure and preparation method

Abstract

The invention discloses a laser structure and a preparation method. The laser structure comprises a substrate; the cross-shaped micro-bridge structure is suspended on a cavity formed in the surface of the substrate through four bridge ends; the multi-quantum well layer is arranged on the cross-shaped micro-bridge structure, and the multi-quantum well layer comprises barrier layers and potential well layers which are alternately arranged in the direction away from the substrate; and the photonic crystal is at least arranged on the bridge surface of the cross-shaped micro-bridge structure and forms a photonic crystal resonant cavity. The optical loss of the laser can be reduced, the quality factor can be remarkably improved, the current threshold value of the laser can be reduced, the thickness of the active area can be reduced, narrow-linewidth and high-quality single-mode emission can be realized, and higher performance and application potential can be achieved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor integrated circuit technology, and in particular to a laser structure and its fabrication method. Background Technology

[0002] GeSn / SiGeSn, as an optoelectronic material, has attracted extensive research into GeSn quantum well lasers due to its tunable band structure and compatibility with CMOS processes. When the Sn content reaches 6.5%–11.0%, the band structure of the GeSn alloy transforms into a direct bandgap, at which point the lattice mismatch between Ge and Sn reaches as high as 15%. However, the solid solubility of Sn in Ge is only 1%, and excessively high Sn content will generate unfavorable compressive strain, making the growth of high-quality, high-tin-content GeSn alloys extremely challenging.

[0003] Meanwhile, in order to obtain low threshold current and high mode factor, and thus offset various optical losses such as free carrier absorption and cavity surface loss, the confinement factor of multi-quantum-well lasers is usually increased by increasing the number of quantum wells (at least a dozen quantum wells are needed to offset internal optical losses and obtain mode gain), which undoubtedly increases the complexity of the process.

[0004] Therefore, research on improving the band structure of GeSn / SiGeSn quantum wells, reducing the threshold current and optical loss of GeSn / SiGeSn quantum well lasers, and increasing the quality factor Q of GeSn / SiGeSn quantum well lasers is of great significance to the development of GeSn / SiGeSn quantum well lasers. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and to provide a laser structure and a method for its fabrication.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a laser structure, comprising:

[0008] Substrate;

[0009] A cross-shaped microbridge structure, which is suspended from a cavity on the surface of the substrate by four bridge ends;

[0010] A multi-quantum well layer is disposed on the cross-shaped microbridge structure, the multi-quantum well layer comprising a barrier layer and a potential well layer alternately arranged along the direction away from the substrate;

[0011] A photonic crystal is disposed at least on the bridge surface of the cross-shaped microbridge structure and forms a photonic crystal resonant cavity.

[0012] Further, the cross-shaped microbridge structure includes a first bridge surface arranged along a first direction and a second bridge surface arranged along a second direction perpendicular to the first direction. The photonic crystal includes a first photonic crystal and a second photonic crystal. The second photonic crystal is located at the intersection of the first bridge surface and the second bridge surface. The first photonic crystal is located on the first bridge surface and the second bridge surface outside the second photonic crystal. The first photonic crystal includes a plurality of first microcavities arranged in an array along the first direction and the second direction. The second photonic crystal includes a plurality of second microcavities and a plurality of third microcavities arranged in an array along the first direction and the second direction. The third microcavities are located on the same side of the second microcavities along the first direction. The diameter of the second microcavities is the same as the diameter of the first microcavities. The diameter of the third microcavities is smaller than the diameter of the second microcavities. The second microcavities are aligned with the first microcavities on the first bridge surface in the first direction, and the second microcavities are aligned with the first microcavities on the second bridge surface in the second direction.

[0013] Furthermore, it also includes a waveguide, which is disposed on the substrate on one side of the first bridge surface along the first direction. The photonic crystal also includes a third photonic crystal disposed on the surface of the waveguide. The third photonic crystal includes a plurality of fourth microcavities arranged along the first direction and located in the waveguide, and the diameter of each fourth microcavity decreases sequentially along the direction away from the first bridge surface.

[0014] Furthermore, the cross-shaped microbridge structure is further provided with an n-type contact layer and a buffer layer located sequentially on the side of the multi-quantum well layer closer to the substrate, and a p-type contact layer located on the other side of the multi-quantum well layer away from the substrate. The p-type contact layer is located on the bridge surface of the cross-shaped microbridge structure, and the first photonic crystal and the second photonic crystal are located in the p-type contact layer.

[0015] Furthermore, the multiple quantum well layer includes SiGeSn barrier layers and GeSn well layers alternately arranged along the direction away from the substrate, the buffer layer includes a SiGeSn buffer layer, the n-type contact layer includes an n-type SiGeSn contact layer, the p-type contact layer includes a p-type SiGeSn contact layer; and / or, the substrate includes an SOI substrate.

[0016] Furthermore, the n-type contact layer and the p-type contact layer are respectively connected to the electrodes; and / or, the cross-shaped microbridge structure is covered with a protective layer.

[0017] Furthermore, the cross-shaped microbridge structure has a bridge deck width that gradually decreases from any one end towards the center.

[0018] The present invention also provides a method for fabricating the above-mentioned laser structure, comprising:

[0019] Provide substrate;

[0020] A cavity is formed on the surface of the substrate, and a cross-shaped microbridge structure is suspended on the cavity. The cross-shaped microbridge structure has a multi-quantum well layer, and a photonic crystal is formed at least on the bridge surface of the cross-shaped microbridge structure. The photonic crystal forms a photonic crystal resonant cavity.

[0021] Furthermore, the method for forming the cavity, the cross-shaped microbridge structure, and the photonic crystal specifically includes:

[0022] A buffer layer, an n-type contact layer, a multiple quantum well layer, and a p-type contact layer are sequentially formed on the surface of the substrate;

[0023] A first photonic crystal formed by a first microcavity and a second photonic crystal formed by a second microcavity and a third microcavity are formed on the surface of the p-type contact layer to form a photonic crystal resonant cavity;

[0024] The p-type contact layer, the multiple quantum well layer, the n-type contact layer, and the buffer layer are patterned to form a cross-shaped microbridge structure, exposing the surface of the substrate;

[0025] Using the exposed substrate surface as a window, a cavity is formed on the substrate surface below the cross-shaped microbridge structure, so that the cross-shaped microbridge structure is suspended in the cavity.

[0026] Furthermore, the method for forming the photonic crystal further includes:

[0027] A waveguide is formed on the substrate surface on one side of the cross-shaped microbridge structure, and a third photonic crystal formed through a fourth microcavity is formed on the surface of the waveguide.

[0028] And / or, also includes:

[0029] Electrodes are formed that connect the n-type contact layer and the p-type contact layer respectively;

[0030] And / or, also includes:

[0031] A protective layer is formed covering the cross-shaped microbridge structure.

[0032] As can be seen from the above technical solution, this invention introduces biaxial tensile strain into the quantum well laser structure by forming a cross-shaped microbridge structure suspended on the substrate. Utilizing the suspension effect, residual tensile strain concentrated towards the center is retained in the cross-shaped microbridge structure, thereby compensating for the insufficient Sn content in the GeSn alloy of the GeSn / SiGeSn quantum well material and the potential problem of biaxial compressive strain. Simultaneously, utilizing the two fundamental properties of photonic crystals—the photonic bandgap and photonic localization—a defect-state photonic crystal resonator formed by combining a first and second photonic crystal is designed and introduced into the cross-shaped microbridge structure. This enables oscillation amplification, reduces optical loss, and significantly improves the quality factor Q of the microcavity, resulting in a lower current threshold for the photonic crystal laser. Furthermore, the introduction of a third photonic crystal with linear defect states into the waveguide makes the light output more stable, thus exhibiting higher performance and application potential. Attached Figure Description

[0033] Figure 1 This is a top view of a laser structure according to a preferred embodiment of the present invention.

[0034] Figure 2 This is a perspective view of a laser structure according to a preferred embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of the layer structure of an active region according to a preferred embodiment of the present invention.

[0036] Figures 4-9 This is a schematic diagram of the process steps for fabricating a laser structure according to a preferred embodiment of the present invention. Detailed Implementation

[0037] 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 clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects.

[0038] The problem this invention aims to solve is that, due to the lower surface free energy of Sn compared to Ge, Sn is more prone to surface segregation during growth. When the Sn content is too high, introducing tensile strain into GeSn to grow a high-tin-content, high-quality GeSn alloy becomes extremely difficult. Furthermore, increasing the number of quantum wells to improve the confinement factor of multi-quantum-well lasers in pursuit of mode gain requires continuously increasing the active region thickness, which undoubtedly increases the complexity of the manufacturing process and results in problems such as high resonant cavity optical loss and a very low Q-factor for the laser.

[0039] Photonic crystals, also known as photonic bandgap materials, are artificially designed and manufactured structures with a periodic distribution of dielectric constant (refractive index). The photonic bandgap (PBG) and photonic localization are the two most important characteristics of photonic crystals. Applying photonic crystals to lasers allows for the control and modulation of light through the manipulation of photon states, enabling continuous reflection and amplification of photons, thus achieving lasing. Furthermore, photonic crystal resonators offer advantages such as high quality factor and small mode volume, significantly enhancing the spontaneous emission efficiency of the laser gain medium, i.e., the Purcell effect. In summary, the unique structure and function of photonic crystals provide new opportunities for the further development and innovation of optical technology and applications.

[0040] The purpose of this invention is to design a GeSn / SiGeSn quantum well laser structure based on photonic crystals. By setting a suspended cross-shaped microbridge structure, compressive strain can be prevented in GeSn. The photonic crystal resonator set on the cross-shaped microbridge structure can improve the quality factor Q of the GeSn / SiGeSn quantum well laser, thereby reducing the threshold current and the thickness of the active region, realizing narrow linewidth and high-quality single-mode emission. Furthermore, by adjusting the parameters of the photonic crystal, the energy loss and resistance loss of the laser can be reduced.

[0041] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0042] refer to Figures 1-3 A laser structure according to the present invention includes a substrate 10, a cross-shaped microbridge structure 13 suspended on the substrate 10, a multiple quantum well (MQWs) layer 16 disposed on the cross-shaped microbridge structure 13, and a photonic crystal 14.

[0043] The cross-shaped microbridge structure 13 has a bridge surface and four bridge ends located at the ends of the bridge surface. A cavity 12 located in the substrate 10 is provided on the surface of the substrate 10 below the cross-shaped microbridge structure 13. The cross-shaped microbridge structure 13 is connected to the surface of the substrate 10 around the cavity 12 through the four bridge ends, thereby being suspended above the cavity 12.

[0044] A multi-quantum well layer 16 is disposed on the cross-shaped microbridge structure 13. The multi-quantum well layer 16 includes a barrier layer 161 and a well layer 162 alternately arranged along the direction away from the substrate.

[0045] The photonic crystal 14 is disposed at least on the bridge surface of the cross-shaped microbridge structure 13, that is, on the multi-quantum well layer 16. The photonic crystal 14 forms a photonic crystal resonant cavity.

[0046] refer to Figures 1-2 In some embodiments, the cross-shaped microbridge structure 13 includes a first bridge surface 132 disposed along a first direction and a second bridge surface 131 disposed along a second direction perpendicular to the first direction. The first bridge surface 132 and the second bridge surface 131 are disposed perpendicular to each other to form the cross-shaped microbridge structure 13. The two ends of the first bridge surface 132 overlap the surfaces of the substrate 10 on two corresponding sides of the cavity 12, and the two ends of the second bridge surface 131 overlap the surfaces of the substrate 10 on the other two corresponding sides of the cavity 12. The first bridge surface 132 and the second bridge surface 131 intersect at the middle of the cross-shaped microbridge structure 13.

[0047] refer to Figures 1-2 In some embodiments, the photonic crystal 14 includes a first photonic crystal 141 and a second photonic crystal 142. The second photonic crystal 142 is located at the intersection of the first bridge surface 132 and the second bridge surface 131, and the first photonic crystal 141 is located on the first bridge surface 132 and the second bridge surface 131 outside the second photonic crystal 142. In other words, the second photonic crystal 142 is located in the middle of the cross-shaped microbridge structure 13 at the intersection of the first bridge surface 132 and the second bridge surface 131, and the first photonic crystal 141 is located on the first bridge surface 132 and the second bridge surface 131 at a non-intersection location outside the middle of the cross-shaped microbridge structure 13.

[0048] In some embodiments, the first photonic crystal 141 includes a plurality of first microcavities 1411 arranged in an array of n rows × m columns along a first direction and a second direction, where n ≥ 2 and m ≥ 2. Each first microcavity 1411 forms a first photonic crystal unit of the first photonic crystal 141.

[0049] In some embodiments, the number of rows and columns of the first photonic crystal 141 in the first direction and the second direction may not be equal.

[0050] The second photonic crystal 142 includes a plurality of second microcavities 1421 arranged in an array of x rows × y columns along a first direction and a second direction, and a plurality of third microcavities 1422 arranged in an array of x rows × y columns along the first direction and the second direction, where x ≥ 2 and y ≥ 2. The third microcavities 1422 are located on the same side of the second microcavities 1421 along the first direction, for example, Figure 1 and Figure 2 The diagram shows that each third microcavity 1422 in the second photonic crystal 142 is located to the left of a corresponding second microcavity 1421. The combination of a second microcavity 1421 and a third microcavity 1422 forms a second photonic crystal unit of the second photonic crystal 142.

[0051] In some embodiments, the first microcavity 1411, the second microcavity 1421, and the third microcavity 1422 are circular cavities. Furthermore, the diameter of the second microcavity 1421 is the same as the diameter of the first microcavity 1411, and the diameter of the third microcavity 1422 is smaller than the diameter of the second microcavity 1421 (and the first microcavity 1411). The diameters of the first microcavity 1411, the second microcavity 1421, and the third microcavity 1422 are on the nanometer scale.

[0052] In some embodiments, the second microcavity 1421 is aligned with the first microcavity 1411 on the first bridge surface 132 in a first direction, and the second microcavity 1421 is also aligned with the first microcavity 1411 on the second bridge surface 131 in a second direction.

[0053] It is worth noting that since the diameter of the second microcavity 1421 is the same as that of the first microcavity 1411, by setting a second microcavity 1421 with the same diameter as the first microcavity 1411 at the intersection of the first bridge surface 132 and the second bridge surface 131, and setting a third microcavity 1422 with a diameter smaller than both the diameters of the second microcavity 1421 and the first microcavity 1411 on one side of the second microcavity 1421, a defect state is introduced into the array of the first photonic crystal 141 on the cross microbridge structure 13, making the formed photonic crystal resonator a defect-state photonic crystal resonator, thereby forming oscillation amplification, reducing optical loss and significantly improving the Q value of the microcavity, thereby reducing the current threshold of the laser.

[0054] refer to Figure 1 In some embodiments, the laser structure further includes a waveguide 15. The waveguide 15 is disposed on a substrate 10 on one side of the first bridge surface 132 along a first direction for light output.

[0055] In some embodiments, the photonic crystal 14 further includes a third photonic crystal 143 disposed on the surface of the waveguide 15. The third photonic crystal 143 includes a plurality of fourth microcavities 1431 arranged along a first direction and located within the waveguide 15. Furthermore, the diameter of each fourth microcavity 1431 decreases sequentially in the direction away from the first bridge surface 132. This generates linear defect states in the third photonic crystal 143, further modulating light propagation and making the light output more stable. The diameter of the fourth microcavities 1431 is on the nanometer scale.

[0056] refer to Figures 1-3In some embodiments, a buffer layer 17, an n-type contact layer 18, a multiple quantum well layer 16, and a p-type contact layer 19 are sequentially disposed on the cross-shaped microbridge structure 13 in a direction away from the substrate 10. The p-type contact layer 19 is located on the bridge surface of the cross-shaped microbridge structure 13, serving as the top layer of the cross-shaped microbridge structure 13. A first photonic crystal 141 and a second photonic crystal 142 are located within the p-type contact layer 19; that is, the first microcavity 1411, the second microcavity 1421, and the third microcavity 1422 have openings on the surface of the p-type contact layer 19, and the bottom surfaces of the first microcavity 1411, the second microcavity 1421, and the third microcavity 1422 are located within the p-type contact layer 19.

[0057] In some embodiments, the multiple quantum well layer 16 includes a SiGeSn barrier layer 161 and a GeSn well layer 162 alternately arranged along a direction away from the substrate 10.

[0058] The buffer layer 17 includes a SiGeSn buffer layer 171.

[0059] The n-type contact layer 18 includes an n-type SiGeSn contact layer 181.

[0060] p-type contact layer 19 includes p-type SiGeSn contact layer 191.

[0061] In some embodiments, substrate 10 includes SOI substrate 101. SOI substrate 101 includes a bottom silicon layer, a buried oxide layer, and a top silicon layer. Cavity 12 and waveguide 15 are disposed on the top silicon layer, and cross-shaped microbridge structure 13 is suspended on the surface of the top silicon layer above cavity 12. Buffer layer 17, n-type contact layer 18, multiple quantum well layer 16, and p-type contact layer 19 also extend beyond cross-shaped microbridge structure 13 to form a planar region 21 surrounding cross-shaped microbridge structure 13. Cross-shaped microbridge structure 13 and planar region 21 are located on the active region. Figure 3 The diagram only shows the film layer hierarchy of the active region, and does not show the cross-shaped microbridge structure 13. The graphic boundaries are not used to represent the actual boundaries of the active region.

[0062] refer to Figures 1-3 In some embodiments, the n-type contact layer 18 and the p-type contact layer 19 are respectively connected to the electrode 11. A first electrode 112 connected to the n-type contact layer 18 is disposed on the top silicon layer surface of the SOI substrate 101 outside the active region (or on the top silicon layer surface between the n-type contact layer 18 and the waveguide 15); a second electrode 111 connected to the p-type contact layer 19 is disposed on the other side of the active region opposite to the first electrode 112, and is located on the surface of the p-type contact layer 19 of the planar region 21. The first electrode 112 and the second electrode 111 can be wired to the pad, wherein the first electrode 112 is used to connect to the voltage Vg.

[0063] In some other embodiments, the n-type SiGeSn contact layer is exposed on one side of the multi-quantum well layer, and contact holes (or TSVs) connected to the Pad are provided on the exposed surface of the n-type SiGeSn contact layer and the surface of the p-type SiGeSn contact layer, respectively, to achieve electrical lead-out.

[0064] In some embodiments, a protective layer 20 covers the cross-shaped microbridge structure 13. The protective layer 20 covers the active region, including the cross-shaped microbridge structure 13, and protects the active region.

[0065] In some embodiments, the cross-shaped microbridge structure 13 has a bridge width that gradually decreases from any one end towards the center. When the substrate 10 is hollowed out to form a cavity 12, the flat plate region 21 surrounding the cross-shaped microbridge structure 13 will generate biaxial tensile stress on the cross-shaped microbridge structure 13, which can concentrate the strain in the central region of the cross-shaped microbridge structure 13 where the bridge width narrows. Using this structure, a large biaxial tensile strain is successfully introduced into the GeSn / SiGeSn quantum well material to compensate for the insufficient Sn content in the GeSn alloy and the potential problem of biaxial compressive strain.

[0066] In some embodiments, the cavity 12 and the photonic crystal resonator together form the resonator of the laser.

[0067] It should be noted that the innovation of this invention lies in the introduction of biaxial tensile strain into the GeSn / SiGeSn quantum well laser structure through a suspended cross-shaped microbridge structure 13, based on bandgap engineering principles, thereby compensating for the insufficient Sn content in the GeSn alloy. The active region of the laser structure adopts a GeSn / SiGeSn multi-quantum-well structure, and the pump source uses electrically injected carriers to achieve population inversion. Utilizing the two fundamental characteristics of photonic bandgap and photonic localization of the photonic crystal 14, a defect-state photonic crystal resonator is designed and introduced. This allows for precise control of the photonic state by confining light within a very small range (a resonant light field with very high energy density), enabling photons to reflect back and forth within the cavity, thereby enhancing the interaction between photons and matter and achieving laser oscillation. This photonic crystal structure achieves a high quality factor and small mode volume, which is beneficial for increasing the spontaneous emission efficiency of the laser, i.e., a large Purcell effect enhancement (the phenomenon that the spontaneous emission rate of an excited atom, quantum dot, or exciton is greatly enhanced when coupled to a resonant cavity. This enhancement is usually due to the electromagnetic field enhancement caused by the resonant cavity, making it more likely that the excited-state particle will return to the ground state by emitting photons). It can also reduce the thickness of the active region to a certain extent, achieving narrow linewidth and high-quality single-mode emission, resulting in a symmetrical laser beam with narrow beam divergence and narrow spectral width. Furthermore, by adjusting the parameters of the photonic crystal 14, the energy loss and resistance loss of the laser can also be reduced.

[0068] The following detailed description, in conjunction with specific embodiments and accompanying drawings, provides a further detailed explanation of a method for fabricating a laser structure according to the present invention.

[0069] A method for fabricating a laser structure according to the present invention includes:

[0070] Provide substrate;

[0071] A cavity is formed on the surface of a substrate, a cross-shaped microbridge structure is formed suspended on the cavity, a multi-quantum well layer is provided on the cross-shaped microbridge structure, and a photonic crystal is formed at least on the bridge surface of the cross-shaped microbridge structure, the photonic crystal forming a photonic crystal resonant cavity.

[0072] refer to Figures 4-9 In some embodiments, a method for fabricating a laser structure according to the present invention can be used to fabricate, for example... Figures 1-2 The laser structure of the present invention is shown, and includes the following steps:

[0073] Step S1: Provide substrate 10.

[0074] like Figure 4 As shown, an SOI substrate 101 is used to further form a laser structure of the present invention on the SOI substrate 101.

[0075] In some embodiments, a cleaning process is used to remove organic contaminants and metal ion contaminants from the surface of the SOI substrate 101, as well as to remove the natural oxide film on the silicon surface of the SOI substrate 101 and passivate the dangling bonds on the silicon surface of the SOI substrate 101.

[0076] Step S2: Form a cross-shaped microbridge structure 13 and a photonic crystal 14 on the surface of the substrate 10.

[0077] In some embodiments, an epitaxial process is used to sequentially form a buffer layer 17, an n-type contact layer 18, a multiple quantum well layer 16, and a p-type contact layer 19 on the surface of an SOI substrate 101.

[0078] like Figure 5 As shown, a SiGeSn buffer layer 171 is first grown on the surface of the SOI substrate 101 to reduce the lattice mismatch between layers.

[0079] In some embodiments, low-pressure chemical vapor deposition (LPCVD) technology is used, with gas sources such as Si2H6, Ge2H6, SnCl4, and N2, and the growth temperature is around 350°C, which can grow a single-crystal SiGeSn buffer layer 171 with good quality on the surface of SOI substrate 101.

[0080] Then, SiGeSn layers and GeSn layers are alternately grown on the surface of SiGeSn buffer layer 171 to form a GeSn / SiGeSn multi-quantum-well layer.

[0081] In some embodiments, such as Figure 6 As shown, ultra-high vacuum chemical vapor deposition (UHVCVD) technology is used, with SnD4 as the gas source for Sn atoms and GeH4 as the gas source for Ge atoms. SiGeSn layers and GeSn layers are alternately grown on the surface of SiGeSn buffer layer 171, and the top layer is SiGeSn layer. Specifically, an n-type SiGeSn contact layer 181 is formed by n-type heavy doping of one SiGeSn layer of an adjacent SiGeSn buffer layer 171, and a p-type SiGeSn contact layer 191 is formed by p-type heavy doping of the top SiGeSn layer. Between the n-type SiGeSn contact layer 181 and the p-type SiGeSn contact layer 191, a SiGeSn barrier layer 161 and a GeSn well layer 162 are formed by alternating layers of SiGeSn and GeSn layers to form a GeSn / SiGeSn multi-quantum-well layer 16. The n-type SiGeSn contact layer 181 and the p-type SiGeSn contact layer 191 serve as the lead-out contact structure layer of the multi-quantum-well layer 16, and their thickness can be greater than that of the SiGeSn barrier layer 161 and the GeSn well layer 162.

[0082] By patterning the SiGeSn buffer layer 171, n-type SiGeSn contact layer 181, multiple quantum well layer 16, and p-type SiGeSn contact layer 191 formed above, an active region is formed on the surface of the SOI substrate 101, such as... Figure 6 As shown. For the specific hierarchical structure of the active region, please refer to [reference needed]. Figure 3 To understand.

[0083] In some embodiments, a waveguide 15 is formed on the surface of the SOI substrate 101 on the active region side by patterning the top silicon layer of the SOI substrate 101, such as... Figure 1 As shown.

[0084] Next, a cross-shaped microbridge structure 13 was fabricated in the active region, and a photonic crystal 14 was fabricated.

[0085] In some embodiments, such as Figure 7As shown, a cross-shaped microbridge structure region and a first photonic crystal and a second photonic crystal region are defined on the surface of the p-type SiGeSn contact layer 191 in the active region by photolithography. Before spin-coating photoresist onto the surface of the p-type SiGeSn contact layer 191, an adhesion promoter is first coated on the surface of the p-type SiGeSn contact layer 191 to enhance the adhesion between the photoresist and the SiGeSn material surface, and then the photoresist is spin-coated onto the adhesion promoter. In this embodiment, a layer of hexamethylsilazane (HDMS) is spin-coated onto the surface of the p-type SiGeSn contact layer 191 as an adhesion promoter, and then a photoresist layer is formed on the hexamethylsilazane layer. In order to control the surface uniformity of the photoresist and prevent the formation of bubbles, a spin coater is used when applying the photoresist. The photoresist is initially spin-coated on the hexamethylsilazane layer at a slow speed (e.g., 450-550 rpm / min, preferably 500 rpm / min) and then at a high speed (e.g., 2500-3500 rpm / min, preferably 3000 rpm / min). After soft baking, the photoresist is exposed.

[0086] Then, an etching process is used to etch the active region to form a cross-shaped microbridge structure 13, as well as a first photonic crystal 141 and a second photonic crystal 142.

[0087] In some embodiments, such as Figure 7 As shown, highly selective and directional inductively coupled plasma (ICP) etching technology is used to etch each film layer (p-type contact layer 19, multiple quantum well layer 16, n-type contact layer 18 and buffer layer 17) in the active region, and preferentially etching the regions of the first photonic crystal 141 and the second photonic crystal 142. The photoresist pattern is transferred to the p-type SiGeSn contact layer 191 on top of the active region through etching. The first photonic crystal 141 formed by the first microcavity 1411 and the second photonic crystal 142 formed by the second microcavity 1421 and the third microcavity 1422 are formed on the surface of the p-type SiGeSn contact layer 191, thereby forming a defect-state photonic crystal resonator.

[0088] Then, further etching is performed to form a cross-shaped microbridge structure 13. For the cross-shaped microbridge structure region, a cross-shaped microbridge structure 13 with a depth slightly greater than the total thickness of each layer in the active region is first etched in the p-type SiGeSn contact layer 191, the multi-quantum well layer 16, the n-type SiGeSn contact layer 181, and the SiGeSn buffer layer 171 in the active region. That is, the buffer layer 17, which is the lowest layer in each layer of the active region, is etched through to expose the surface of the SOI substrate 101, forming a wet etching window 22. A flat plate region 21 is formed around the cross-shaped microbridge structure 13, and the width of the first bridge surface 132 and the second bridge surface 131, which intersect in a cross shape on the cross-shaped microbridge structure 13, gradually decreases from the bridge ends at the edge to the middle. At this time, a smaller initial tensile strain can be obtained.

[0089] By employing inductively coupled plasma etching to etch the photolithographically etched active region, not only can better etching directionality be obtained, but the etching speed is also greatly improved. This enables the formation of sidewalls of a cross-shaped microbridge structure 13 with high steepness in depth and uniform, smooth width.

[0090] Step S3: A cavity 12 is formed on the surface of the substrate 10 below the cross microbridge structure 13, so that the cross microbridge structure 13 is suspended on the cavity 12.

[0091] like Figure 8 As shown, a wet etching process is then employed, and the surface of the exposed SOI substrate 101 (top silicon layer surface) is etched through the wet etching window 22 to form a cavity 12 on the surface of the SOI substrate 101 below the cross-shaped microbridge structure 13. This allows the cross-shaped microbridge structure 13 to be suspended over the opening of the cavity 12. The bridge ends of the first bridge surface 132 and the second bridge surface 131 on the cross-shaped microbridge structure 13 are connected to the flat plate region 21, and the edge of the cavity 12 is located below the bridge ends, allowing the cross-shaped microbridge structure 13 to be suspended from the surface of the SOI substrate 101 surrounding the cavity 12 via its four bridge ends.

[0092] In some embodiments, a tetramethylammonium hydroxide (TMAH) solution with a concentration of 4-8%, preferably 5%, is used to etch the silicon material on the SOI substrate 101 beneath the cross-shaped microbridge structure 13. After the cross-shaped microbridge structure 13 loses the constraint of the SOI substrate 101, due to the gradually decreasing width from the edge to the center of the first bridge surface 132 and the second bridge surface 131, the surrounding flat plate region 21 will exert biaxial tension on the central region of the cross-shaped microbridge structure 13 at the intersection of the first bridge surface 132 and the second bridge surface 131. This causes a redistribution of the initial tensile strain of the various film layers on the cross-shaped microbridge structure 13, thereby concentrating the strain in the central region of the cross-shaped microbridge structure 13.

[0093] In some embodiments, photolithography and etching processes can also be used to form a third photonic crystal 143 formed through the fourth microcavity 1431 on the surface of the waveguide 15, such as... Figure 1 As shown.

[0094] Step S4: Form electrode 11.

[0095] In some embodiments, such as Figure 9 As shown, using electron beam evaporation (EBE) or physical vapor deposition (PVD) techniques, Au, Ti, Al, and other electrode metals are deposited on the surface of the p-type SiGeSn contact layer 191 and the SOI substrate 101 on one side of the n-type SiGeSn contact layer 181, and patterned first electrode 112 and second electrode 111 are formed to connect the n-type SiGeSn contact layer 181 and the p-type SiGeSn contact layer 191, respectively, thereby forming an electric pump electrode 11, which is then led to Pad.

[0096] In some other embodiments, it may be unnecessary to fabricate the first electrode 112 and the second electrode 111 described above. This can be achieved by exposing the n-type SiGeSn contact layer on one side of the multi-quantum-well layer, and fabricating contact holes (or TSVs) connected to the Pad on the exposed surface of the n-type SiGeSn contact layer and the surface of the p-type SiGeSn contact layer, respectively.

[0097] In some embodiments, a deposition process may be used to further form a dielectric protective layer 20 covering the active region, including the cross-shaped microbridge structure 13. This completes the fabrication of the germanium-tin quantum well electrically pumped laser structure based on photonic crystals according to the present invention.

[0098] In summary, this invention introduces biaxial tensile strain into the quantum well laser structure by forming a cross-shaped microbridge structure 13 suspended on the substrate 10. Utilizing the suspension effect, residual tensile strain concentrated towards the center is retained in the cross-shaped microbridge structure 13, thereby compensating for the insufficient Sn content in the GeSn alloy of the GeSn / SiGeSn quantum well material and the potential problem of biaxial compressive strain. Simultaneously, leveraging the fundamental properties of the photonic bandgap and photonic localization of the photonic crystal 14, a defect-state photonic crystal resonator formed by combining a first photonic crystal 141 and a second photonic crystal 142 is designed and introduced into the cross-shaped microbridge structure 13. This enables oscillation amplification, reduces optical loss, and significantly improves the quality factor Q of the microcavity, resulting in a lower current threshold for the photonic crystal laser. Furthermore, the introduction of a third photonic crystal 143 with linear defect states into the waveguide 15 makes the light output more stable, thus exhibiting higher performance and application potential.

[0099] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A laser structure, characterized in that, include: Substrate; A cross-shaped microbridge structure, which is suspended from a cavity on the surface of the substrate by four bridge ends; A multi-quantum well layer is disposed on the cross-shaped microbridge structure, the multi-quantum well layer comprising a barrier layer and a potential well layer alternately arranged along the direction away from the substrate; A photonic crystal is disposed at least on the bridge surface of the cross-shaped microbridge structure and forms a photonic crystal resonant cavity.

2. The laser structure according to claim 1, characterized in that, The cross-shaped microbridge structure includes a first bridge surface arranged along a first direction and a second bridge surface arranged along a second direction perpendicular to the first direction. The photonic crystal includes a first photonic crystal and a second photonic crystal. The second photonic crystal is located at the intersection of the first bridge surface and the second bridge surface. The first photonic crystal is located on the first bridge surface and the second bridge surface outside the second photonic crystal. The first photonic crystal includes a plurality of first microcavities arranged in an array along the first direction and the second direction. The second photonic crystal includes a plurality of second microcavities and a plurality of third microcavities arranged in an array along the first direction and the second direction. The third microcavities are located on the same side of the second microcavities along the first direction. The diameter of the second microcavities is the same as the diameter of the first microcavities. The diameter of the third microcavities is smaller than the diameter of the second microcavities. The second microcavities are aligned with the first microcavities on the first bridge surface in the first direction, and the second microcavities are aligned with the first microcavities on the second bridge surface in the second direction.

3. The laser structure according to claim 2, characterized in that, It also includes a waveguide, which is disposed on the substrate on one side of the first bridge surface along the first direction. The photonic crystal also includes a third photonic crystal disposed on the surface of the waveguide. The third photonic crystal includes a plurality of fourth microcavities arranged along the first direction and located in the waveguide, and the diameter of each fourth microcavity decreases sequentially along the direction away from the first bridge surface.

4. The laser structure according to claim 2, characterized in that, The cross-shaped microbridge structure is further provided with an n-type contact layer and a buffer layer located sequentially on the side of the multi-quantum well layer closer to the substrate, and a p-type contact layer located on the other side of the multi-quantum well layer away from the substrate. The p-type contact layer is located on the bridge surface of the cross-shaped microbridge structure, and the first photonic crystal and the second photonic crystal are located in the p-type contact layer.

5. The laser structure according to claim 4, characterized in that, The multiple quantum well layer includes alternating SiGeSn barrier layers and GeSn well layers along a direction away from the substrate; the buffer layer includes a SiGeSn buffer layer; the n-type contact layer includes an n-type SiGeSn contact layer; the p-type contact layer includes a p-type SiGeSn contact layer; and / or, the substrate includes an SOI substrate.

6. The laser structure according to claim 4, characterized in that, The n-type contact layer and the p-type contact layer are respectively connected to the electrodes; and / or, the cross-shaped microbridge structure is covered with a protective layer.

7. The laser structure according to claim 1, characterized in that, The cross-shaped microbridge structure has a bridge deck width that gradually decreases from any one end toward the center.

8. A method for fabricating a laser structure according to any one of claims 1-7, characterized in that, include: Provide substrate; A cavity is formed on the surface of the substrate, and a cross-shaped microbridge structure is suspended on the cavity. The cross-shaped microbridge structure has a multi-quantum well layer, and a photonic crystal is formed at least on the bridge surface of the cross-shaped microbridge structure. The photonic crystal forms a photonic crystal resonant cavity.

9. The method for fabricating a laser structure according to claim 8, characterized in that, The method for forming the cavity, the cross-shaped microbridge structure, and the photonic crystal specifically includes: A buffer layer, an n-type contact layer, a multiple quantum well layer, and a p-type contact layer are sequentially formed on the surface of the substrate; A first photonic crystal formed by a first microcavity and a second photonic crystal formed by a second microcavity and a third microcavity are formed on the surface of the p-type contact layer to form a photonic crystal resonant cavity; The p-type contact layer, the multiple quantum well layer, the n-type contact layer, and the buffer layer are patterned to form a cross-shaped microbridge structure, exposing the surface of the substrate; Using the exposed substrate surface as a window, a cavity is formed on the substrate surface below the cross-shaped microbridge structure, so that the cross-shaped microbridge structure is suspended in the cavity.

10. The method for fabricating a laser structure according to claim 9, characterized in that, The method for forming the photonic crystal further includes: A waveguide is formed on the substrate surface on one side of the cross-shaped microbridge structure, and a third photonic crystal formed through a fourth microcavity is formed on the surface of the waveguide. And / or, also includes: Electrodes are formed that connect the n-type contact layer and the p-type contact layer respectively; And / or, also includes: A protective layer is formed covering the cross-shaped microbridge structure.

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