Preparation method of band gap tunable semiconductor three-dimensional micro-nano structure

Abstract

The application belongs to the technical field of semiconductor device manufacturing, and specifically discloses a preparation method of a semiconductor three-dimensional micro-nano structure with tunable band gap, which comprises the following steps: heating a semiconductor core optical fiber according to a target heating temperature, and controlling the cooling rate of the optical fiber during cooling; the heating process and the cooling rate have a corresponding relationship with the stress applied on the fiber core and the related semiconductor three-dimensional micro-nano structure during heating of the optical fiber, and the stress can be used to tune the band gap of the semiconductor three-dimensional micro-nano structure; wherein, in the case that the target heating temperature is higher than the melting point of the fiber core, the optical fiber is locally heated to apply a controllable compressive stress on the fiber core so that the fiber core forms a semiconductor three-dimensional micro-nano structure and the band gap structure thereof is tuned; in the case that the target heating temperature is lower than the melting point of the fiber core, the optical fiber is heated as a whole so that the semiconductor three-dimensional micro-nano structure is recrystallized, a tensile stress is applied on the semiconductor three-dimensional micro-nano structure by using the volume difference between the recrystallized structure and the original structure, and the band gap structure thereof is tuned.

Description

Technical Field

[0001] This application belongs to the field of semiconductor device manufacturing technology, and more specifically, relates to a method for fabricating a bandgap tunable semiconductor three-dimensional micro / nano structure. Background Technology

[0002] In recent years, although silicon photonics has been widely applied and researched in integrated circuits, existing silicon-based materials are severely limited in terms of technological advancements and performance improvements for future devices, resulting in a current lack of suitable semiconductor materials for devices. Semiconductor materials and devices are the foundation for many key technologies, including electronics, computing, communications, optoelectronics, and sensing, and the bandgap structure of semiconductors is a key factor determining their electrical and optical properties. Current developments in electrical and optical technologies aim not only to adjust the properties of semiconductors but also to miniaturize the corresponding devices.

[0003] To overcome the limitations of semiconductors in optoelectronic performance, researchers have introduced strain modulation techniques. By precisely controlling the type and magnitude of strain, the crystal structure of semiconductor materials can be altered, enabling the tuning of the semiconductor bandgap. However, current strain engineering-based bandgap tuning methods involve complex procedures and high costs, and their functionality is limited, only able to reduce or increase the bandgap, failing to meet both requirements simultaneously. Furthermore, samples prepared using these techniques are large, making them unsuitable for the high-density integration requirements of electronic devices. In recent years, with the deepening research on strain modulation of two-dimensional materials, researchers have reached near-limits at almost every level. However, influenced by Moore's Law, three-dimensional integration technology will gradually develop, opening new avenues for the exploration of three-dimensional materials. Strain modulation techniques for three-dimensional materials hold promise for overcoming the limitations of two-dimensional strain modulation, achieving more efficient and flexible bandgap control. How to conveniently fabricate semiconductor three-dimensional micro / nanostructures and precisely control their bandgap is a pressing technical problem in this field. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to realize the convenient fabrication of semiconductor three-dimensional micro-nano structures and the precise control of the band gap of semiconductor three-dimensional micro-nano structures.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure, the method comprising:

[0006] The optical fiber is heated to a target heating temperature, and the cooling rate during cooling is controlled. The heating process and cooling rate are related to the stress applied to the fiber core and related semiconductor three-dimensional micro / nano structures during the heating of the optical fiber. This stress can be used to tune the semiconductor bandgap.

[0007] In the case that the target heating temperature is higher than the melting point of the core, the optical fiber is locally heated to exert a compressive controllable stress on the core and form a semiconductor three-dimensional micro-nano structure and tune its bandgap structure; in the case that the target heating temperature is lower than the melting point of the core, the optical fiber is heated as a whole to recrystallize the semiconductor three-dimensional micro-nano structure, exert a tensile stress on the semiconductor three-dimensional micro-nano structure by virtue of the volume difference between the recrystallized structure and the original structure, and tune its bandgap structure.

[0008] In the heating process, the optical fiber can be locally heated when the target heating temperature is higher than the melting point of the core, for example, the target region is heated by a first heating source (to be described later); the optical fiber can also be heated as a whole when the target heating temperature is lower than the melting point of the core, for example, the optical fiber treated by the first heating source is heated as a whole by a second heating source (to be described later).

[0009] The principle of preparing the semiconductor three-dimensional micro-nano structure is that the energy of the heating source is mainly absorbed by the semiconductor material due to the difference in the absorption coefficient of the heating source between the semiconductor material (core) and the cladding. The absorbed energy causes the core to begin to liquefy. Under the action of capillary instability, the surface tension and viscoelastic force between the core and the cladding jointly cause the liquefied cylindrical core to split into a plurality of droplets in the cladding. Under certain temperature and stress conditions, these droplets can form micro-nano structures such as spherical, ellipsoidal or rod-shaped, which mainly depend on the thermal expansion properties of the optical fiber, the stress distribution in the heating process and the initial shape of the optical fiber. When the optical fiber is uniformly heated, the semiconductor material is subjected to uniform stress in all directions, thereby forming stable spherical droplets. However, when the optical fiber is subjected to non-uniform heating or generates non-uniform stress distribution (the optical fiber moves at a non-uniform speed, which can generate non-uniform stress distribution), the stress in the semiconductor material is larger in a certain direction, which causes the core to possibly form ellipsoidal or rod-shaped. Finally, as the heating source moves away from the optical fiber, the cladding and the semiconductor droplets begin to solidify in sequence, thereby forming a semiconductor three-dimensional micro-nano structure in the optical fiber.

[0010] The principle of tuning the bandgap of the semiconductor three-dimensional micro-nano structure is to influence the thermal stress and the degree of crystallization of the semiconductor material (core) in the optical fiber by precisely controlling the cooling rate of the thermal treatment of the optical fiber. Due to the difference in the cooling rate, different types and sizes of internal stress are generated in the semiconductor material during the thermal treatment of the optical fiber. These internal stresses affect the crystal structure of the semiconductor material, and further affect its energy band structure, thereby achieving the purpose of tuning the bandgap.

[0011] Specifically, the thermal stress of the semiconductor material is caused by the difference in thermal expansion coefficient between the core and the cladding material, resulting in volume mismatch. Some materials (such as silicon, germanium) will exhibit abnormal expansion characteristics when they reach a certain temperature during cooling. In addition, the melting point of these semiconductor materials (core) is lower than the softening point of the cladding (such as silica).

[0012] In the first case, the heating source heats the fiber core to a molten state. When the optical fiber begins to cool, the silica cladding first solidifies and forms a fixed cavity, the volume of which is determined by the cooling rate. The faster the cooling rate, the smaller the silica density, and the smaller the fixed cavity it forms. Subsequently, the semiconductor material reaches the solidification temperature (melting point) and changes from a liquid state to a solid state. During the cooling process, the volume of the semiconductor material begins to increase due to its abnormal expansion characteristics, which is restricted and compressed by the surrounding cladding. This volume mismatch causes compression stress inside the semiconductor material. The cooling rate mainly affects the volume of the cladding when it solidifies, thereby affecting the internal stress of the semiconductor material. A faster cooling rate will cause the cladding to still maintain the material properties at high temperature, resulting in a larger volume, which further restricts the space of the semiconductor material and causes greater compression stress inside it.

[0013] In the second case, the heating source only moderately heats the cladding of the optical fiber and does not reach a molten state, and the heating temperature is lower than the melting point of the core. Under this condition, the semiconductor material mainly undergoes a low-temperature recrystallization process. During the heating and cooling process of the optical fiber, due to the distribution of temperature gradient, the semiconductor crystal begins to recrystallize. During crystal growth, new crystal orientations gradually form, internal defects are eliminated or reduced, and the internal structure begins to rearrange, forming a more compact and ordered crystal structure, which leads to a decrease in crystal volume. As the volume of the semiconductor material shrinks, the cladding material hardly expands and shrinks, and its volume changes little. Therefore, this volume mismatch causes tensile stress inside the semiconductor material. The cooling rate directly affects the degree of crystallization of the crystal, and in turn affects the volume change and internal stress of the semiconductor material. A faster cooling rate will shorten the crystal growth time, form smaller crystals, and further reduce the crystal volume, thereby generating greater tensile stress. In practical applications, the situation is often more complex than theory, and only one of the two cases can be analyzed.

[0014] In one possible implementation, the heating of the optical fiber according to the target heating temperature and the control of the cooling rate of the optical fiber during cooling include:

[0015] The target region is heated by the first heating source, and during the heating process, the optical fiber enters and leaves the target region at the target moving speed, so that the fiber core forms a semiconductor three-dimensional micro-nano structure, the target region and the optical fiber are located in the same horizontal plane, the target heating temperature is the temperature of the center of the target region, the temperature of the center of the target region is higher than the melting point of the fiber core of the optical fiber, and the optical fiber has a first cooling rate during the process of leaving the target region.

[0016] The first heating source can select a high-energy light source such as a laser to ensure that the fiber core can reach the melting point. By adjusting the output power of the laser, a sufficient heating temperature can be obtained. By adjusting the height of the laser, the size of the laser spot can be changed. By adjusting the size of the laser spot, the cooling rate of the heat treatment of the optical fiber can be further controlled. The size of the laser spot determines the size of the area irradiated by the laser (i.e. the above-mentioned target region), and under the condition that other variables remain unchanged, the larger the spot size, the larger the laser irradiation area, the smaller the temperature gradient of the heated part of the optical fiber, and the slower the heat treatment cooling rate. Therefore, the cooling rate of the optical fiber can be adjusted according to different laser spot sizes. When the spot size is large, the cooling rate is slow, and when the spot size is small, the cooling rate is fast.

[0017] In a possible implementation, in the case that the first heating source uniformly heats the target region, the shape of the semiconductor three-dimensional micro-nano structure is spherical;

[0018] In the case that the first heating source non-uniformly heats the target region, the shape of the semiconductor three-dimensional micro-nano structure is non-spherical.

[0019] In a possible implementation, the first heating source is a laser, and before the target region is heated by the first heating source, the method further comprises:

[0020] Adjusting the height of the laser to determine the spot size formed by the laser emitted by the laser in the target region, the spot size affecting the speed of the cooling rate, the smaller the spot size, the faster the first cooling rate.

[0021] In a possible implementation, the method further comprises:

[0022] Collecting an image of the optical fiber in the target region;

[0023] Displaying the image and receiving a target input, the image being used to calculate and quantify the numerical value of the cooling rate by using the blackbody radiation principle, and the target input being used to indicate the adjustment amount of the moving speed and the adjustment amount of the output power of the laser;

[0024] In response to the target input, the target moving speed of the optical fiber and the output power of the laser are controlled based on the adjustment amount of the moving speed and the adjustment amount of the output power.

[0025] In a possible implementation, the method further includes:

[0026] The displacement table is used to carry the optical fiber to move at a target moving speed in the process of heating the target area by the first heating source.

[0027] In a possible implementation, the heating the optical fiber at the target heating temperature and controlling a cooling rate of the optical fiber when the optical fiber is cooled includes:

[0028] The second heating source is used to heat the optical fiber processed by the first heating source as a whole to recrystallize the semiconductor three-dimensional micro-nano structure in the optical fiber, the second heating source provides a target heating temperature lower than a melting point of the fiber core for the optical fiber, the whole heating process includes a warming-up stage of warming up from a preset temperature to the target heating temperature, a holding stage, and a cooling-down stage of cooling down from the target heating temperature to the preset temperature, and the cooling-down stage has a second cooling rate.

[0029] The second heating source can be a tube furnace, and the cooling rate of the optical fiber is controlled by setting the cooling rate in the tube furnace. However, the tube furnace and the laser have different heating methods. The laser can heat the optical fiber locally, but the tube furnace cannot. Therefore, the laser is suitable for the preparation of the semiconductor three-dimensional micro-nano structure and the band gap tuning, and the tube furnace is suitable for tuning the band gap but not for the preparation of the semiconductor three-dimensional micro-nano structure.

[0030] The tube furnace can meet the requirements of placing and heating the semiconductor three-dimensional micro-nano structure, and can adjust the temperature in the tube furnace according to the target temperature in the tube furnace, the warming-up and cooling-down rates, and the holding time.

[0031] Specifically, the temperature in the tube furnace is the recrystallization temperature of the fiber core, which needs to be set below the melting point of the semiconductor material to ensure that the material will not melt and is suitable for crystal growth. The holding time needs to be set sufficiently to allow the fiber core to be fully affected by thermal stress and allow the crystal to have sufficient time for growth and rearrangement. The cooling rate of the optical fiber, that is, the cooling rate, will affect the crystallization degree of the semiconductor crystal. Therefore, an appropriate rate needs to be selected to ensure that the internal stress can still be retained after cooling.

[0032] In a possible implementation, the second heating source is a tube furnace.

[0033] The tube furnace is used to carry the optical fiber containing the semiconductor three-dimensional micro-nano structure processed by the first heating source, and adjust the temperature in the tube furnace according to the target temperature in the tube furnace, the warming-up rate, the cooling-down rate, and the holding time in the tube furnace in a vacuum environment, the target temperature in the tube furnace is the target heating temperature, and the cooling-down rate is the second cooling rate.

[0034] In a second aspect, the application also provides a device for preparing a semiconductor three-dimensional micro-nano structure with tunable band gap, comprising a bearing table and a heating module.

[0035] The bearing table is used for placing the optical fiber.

[0036] The heating module is used for heating the optical fiber according to a target heating temperature and controlling the cooling rate of the optical fiber when it is cooled. The heating process and the cooling rate have a corresponding relationship with the stress applied to the fiber core and the related semiconductor three-dimensional micro-nano structure when the fiber core is heated, and the stress can be used to tune the semiconductor band gap.

[0037] In the case where the target heating temperature is higher than the melting point of the fiber core, the optical fiber is locally heated to apply a controllable compressive stress to the fiber core to form a semiconductor three-dimensional micro-nano structure and tune its band gap structure. In the case where the target heating temperature is lower than the melting point of the fiber core, the optical fiber is heated as a whole to recrystallize the semiconductor three-dimensional micro-nano structure, apply a tensile stress to the semiconductor three-dimensional micro-nano structure by using the volume difference between the recrystallized structure and the original structure, and tune its band gap structure.

[0038] In a possible implementation, the bearing table can be a displacement table, and the heating module comprises a heating source and a controller (such as a control computer), and the heating source and the displacement table are connected with the controller respectively.

[0039] The heating source is used for providing necessary heat and corresponding cooling rate for the optical fiber.

[0040] The displacement table is used for placing the optical fiber and carrying the optical fiber to move.

[0041] The controller is used for controlling the moving speed of the optical fiber and responsible for setting and adjusting the equipment parameters of the heating source.

[0042] It should be noted that if the heating source is movable, the displacement table can also be any platform capable of placing the optical fiber.

[0043] Specifically, the controller regulates the displacement table according to the required heating length and moving speed of the optical fiber, and adjusts the output power of the laser according to the melting points of the fiber core and the cladding to ensure that the fiber core has sufficient heating time and heating temperature to form a molten state.

[0044] It can be understood that the optical fiber is introduced into the laser irradiation area and is locally heated, and the fiber core reaches the melting point by adjusting the moving speed of the optical fiber and the output power of the laser, thereby forming different semiconductor three-dimensional micro-nano structures. By adjusting the size of the laser spot, the compression stress applied to the semiconductor three-dimensional micro-nano structure can be further regulated. In addition, by placing the optical fiber containing the semiconductor three-dimensional micro-nano structure into a tube furnace and performing a low-temperature recrystallization process, a corresponding tensile stress can be applied. The compression stress and the tensile stress can change the energy band structure of the semiconductor, thereby realizing bandgap tuning of the semiconductor three-dimensional micro-nano structure.

[0045] Therefore, by using the preparation device composed of the heating source, the displacement table and the controller, the semiconductor three-dimensional micro-nano structure can be conveniently prepared, and by adjusting the heat treatment cooling rate of the optical fiber, the bandgap of the semiconductor three-dimensional micro-nano structure can be regulated.

[0046] In a possible implementation, the optical fiber has a semiconductor material as the fiber core.

[0047] In a possible implementation, the preparation device further comprises a camera, wherein the camera is connected to the controller.

[0048] The camera is configured to capture an image of the optical fiber at the light-emitting position and send the captured image to the controller.

[0049] The controller is specifically configured to display the image and adjust the moving speed and the output power of the laser accordingly.

[0050] Specifically, the camera position and the focal length are adjusted to be vertically aligned with the light-emitting position of the laser, so as to observe the temperature distribution of the optical fiber during heating; and the controller is further configured to adjust the image parameters of the camera.

[0051] From the captured image, it can be observed that the heating area of the optical fiber appears a solid-liquid alternating interface, which indicates that the optical fiber has reached the preparation condition. The image can also be used to calculate the cooling rate of the optical fiber by using the blackbody radiation principle.

[0052] In a third aspect, the application also provides a semiconductor three-dimensional micro-nano structure, which is prepared by the preparation method described in the first aspect or any possible implementation of the first aspect.

[0053] Overall, compared with the prior art, the above technical solutions conceived by the application have the following beneficial effects:

[0054] (1) A preparation principle of a bandgap tunable semiconductor three-dimensional micro-nano structure is adopted. The principle can not only prepare various types of semiconductor three-dimensional micro-nano structures, but also control the stress and bandgap of the semiconductor. By changing the heating mode (uniform heating or non-uniform heating) of the heating source, different shapes of micro-nano structures such as spherical, ellipsoidal and rod-shaped can be prepared. In addition, by controlling the heating process and cooling rate of the heating source, the thermal stress and crystallization degree of the semiconductor can be affected, so that compression stress and tensile stress can be applied to the semiconductor, thereby affecting its energy band structure and realizing bandgap tuning.

[0055] (2) By locally heating the optical fiber with a laser, only using laser irradiation, and by adjusting the optical fiber moving speed, laser spot size and power, the corresponding compression stress (strain) can be applied to the semiconductor three-dimensional micro-nano structure, thereby affecting the energy band structure of the semiconductor. For direct bandgap materials, compression strain usually leads to a decrease in bandgap. This is because compression strain reduces the energy difference between the conduction band and the valence band, thereby reducing the bandgap. For indirect bandgap materials, the effect of compression strain can be more complex. In some cases, compression strain can cause the bandgap to increase, because compression strain can change the position of the energy valley, making it more difficult for electrons to transition from the valence band to the conduction band.

[0056] (3) By placing the optical fiber in a tube furnace for low-temperature recrystallization treatment, adjusting the furnace temperature, holding time and heating and cooling rate of the tube furnace, the corresponding tensile stress (strain) can be applied to the semiconductor three-dimensional micro-nano structure, thereby affecting the energy band structure of the semiconductor. For direct bandgap materials, tensile strain usually leads to an increase in bandgap. This is because tensile strain increases the energy difference between the conduction band and the valence band, thereby increasing the bandgap. For indirect bandgap materials, the effect of tensile strain can also be more complex. In some cases, tensile strain can cause the bandgap to decrease, because tensile strain can change the position of the energy valley, making it easier for electrons to transition from the valence band to the conduction band. The above processes do not require any complex processes such as deposition, sputtering or plating, and do not rely on large and expensive equipment, simplifying the manufacturing process and reducing production costs.

[0057] (4) The bandgap tunable semiconductor three-dimensional micro-nano structure produced by the above preparation device and method not only meets the needs of different bandgap semiconductors, but also has tunability, especially the diameter of the spherical shape can be selected, which is convenient for high integration with electronic devices and can maintain good compatibility with traditional silicon-based devices. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a schematic diagram of a method for preparing a semiconductor three-dimensional micro-nano structure and adjusting the bandgap of the semiconductor three-dimensional micro-nano structure by using a laser provided by the embodiments of the present application;

[0059] Figure 2 is a Raman spectrum of a semiconductor germanium ball after laser-induced recrystallization provided by an embodiment of the present application;

[0060] Figure 3 is a flow chart of a method for heating a semiconductor three-dimensional micro-nano structure and adjusting a band gap of the semiconductor three-dimensional micro-nano structure by using a tube furnace provided by an embodiment of the present application;

[0061] Figure 4 is a comparison chart of Raman spectra of semiconductor germanium balls after laser-induced recrystallization and low-temperature recrystallization provided by an embodiment of the present application;

[0062] Figure 5 is a comparison chart of photoluminescence spectra of semiconductor germanium balls at room temperature after laser-induced recrystallization and low-temperature recrystallization provided by an embodiment of the present application;

[0063] Figure 6 is an optical microscope chart of a free-standing semiconductor silicon ball provided by an embodiment of the present application.

[0064] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0065] 1: laser; 2: camera; 3: motorized displacement stage; 4: control computer; 5: semiconductor core optical fiber; 6: semiconductor three-dimensional micro-nano structure. DETAILED DESCRIPTION

[0066] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0067] In the embodiments of the present application, the words such as “exemplary” or “for example” are used to represent an example, illustration or description. Any embodiment or design scheme described as “exemplary” or “for example” in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. In fact, the words such as “exemplary” or “for example” are intended to present the related concept in a specific manner.

[0068] In the description of the embodiments of the present application, unless otherwise specified, “a plurality of” means two or more, for example, a plurality of processing units means two or more processing units, and the like; a plurality of elements means two or more elements, and the like.

[0069] Firstly, the technical terms involved in the embodiments of the present application are introduced.

[0070] (1) Indirect bandgap semiconductor: In indirect bandgap semiconductors, the bottom of the conduction band and the top of the valence band are not in the same Brillouin zone, and electrons need to rely on phonons (lattice vibrations) to meet the momentum conservation condition when jumping from the conduction band to the valence band. This makes the emission and absorption efficiency of light lower. Common indirect bandgap semiconductor materials are silicon, germanium, and indium arsenide, etc.

[0071] (2) Direct bandgap semiconductor: In direct bandgap semiconductors, the bottom of the conduction band and the top of the valence band are in the same Brillouin zone, and the electron transition does not need the participation of phonons, so the emission and absorption efficiency of light is higher, which is suitable for optoelectronic devices such as lasers and photodetectors. Common direct bandgap semiconductor materials are gallium arsenide, indium phosphide, and gallium nitride, etc.

[0072] (3) Strain regulation technology: Strain regulation technology mainly changes the lattice structure and band structure of the material by applying stress, so as to realize the regulation of the physical properties of the material. Strain types: mainly include tensile strain and compressive strain. Common ways to apply stress are: stretching or compressing the material by mechanical means, introducing strain by using the thermal expansion or contraction of the material during heating or cooling, introducing stress in the material by chemical reaction (such as chemical vapor deposition method), etc. Using different stress methods or applying different types of strain will have different effects on the band structure, electron mobility, carrier concentration, etc. of the material.

[0073] (4) Band structure: The band structure of a solid material is composed of multiple energy bands, and the energy bands are divided into conduction band, valence band and forbidden band, etc. The gap between the conduction band and the valence band is called forbidden band (energy gap).

[0074] (5) Three-dimensional micro-nano structure of semiconductor: A semiconductor material structure with a size of microns or nanometers and certain functions formed by advanced micro-processing technology or material growth process. These structures exhibit unique electronic, optical and thermal properties by precisely controlling the size, shape and surface properties of the material.

[0075] The embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0076] Embodiment 1 and Embodiment 2 are illustrated by taking the semiconductor core optical fiber with pure germanium as the core and aluminosilicate glass as the cladding as an example. The special optical fiber is selected as the embodiment mainly because the cladding and the core have similar melting points, which can effectively avoid the rupture of the semiconductor three-dimensional micro-nano structure in the optical fiber due to excessive stress, and facilitate the subsequent acquisition of the complete semiconductor three-dimensional micro-nano structure. According to the actual application requirements, the cladding material is not limited to silica, but can also be silicate, borosilicate, phosphate, etc., and the physical properties of the cladding can be adjusted by doping different substances. In addition to germanium, the core can also be other materials that need to be made into micro-nano structures, such as silicon and other crystal materials, Zns, CdTe, ZnSe, etc. II-VI group materials, InSb, InP, InAs, etc. III-V group materials, gold, tin, lithium or other alloys. However, regardless of the material of the cladding and the core, the thermal and mechanical properties thereof should meet the requirements of the optical fiber fusion hot drawing process and the formation of the semiconductor three-dimensional micro-nano structure.

[0077] Embodiment 1: An apparatus and method for producing semiconductor three-dimensional micro-nano structures and adjusting the band gap of semiconductor three-dimensional micro-nano structures by using a laser to control the cooling rate.

[0078] Reference Figure 1 , the present application provides an apparatus for producing semiconductor three-dimensional micro-nano structures and adjusting the semiconductor three-dimensional micro-nano structures, which comprises a laser 1, a camera 2 and an electric displacement table 3, all of which are connected with a control computer 4. The electric displacement table 3 is used to place a semiconductor core optical fiber 5, adjust the heating length and moving speed of the semiconductor core optical fiber 5; the laser 1 is vertically placed above the electric displacement table 3, the size of the laser spot is changed by adjusting the height, and the emitted laser beam locally heats the semiconductor core optical fiber 5 on the electric displacement table 3; the camera 2 is located directly in front of the laser heating area, which is used to observe the temperature distribution of the semiconductor core optical fiber 5 during heating; and the control computer 4 is used to control the moving distance and speed of the electric displacement table 3, adjust the output power of the laser 1 and the image parameters of the camera 2. Figure 1 In the middle represents the moving speed of the optical fiber.

[0079] The working principle of producing semiconductor three-dimensional micro-nano structures by using a laser is as follows. The semiconductor core optical fiber 5 used in the present embodiment, due to the different absorption coefficients of the germanium core and the cladding, the energy of the laser is mainly absorbed by the core, and the absorbed laser energy liquefies the core. Under the action of capillary instability, due to the surface tension and viscoelastic force between the core and the cladding material, the liquefied cylindrical core is split into multiple droplets in the cladding. As the optical fiber moves away from the laser heating area, the cladding solidifies first due to its higher melting point than the core, and then the spherical droplets gradually cool and solidify, as shown in Figure 1 , finally forming a solid-state semiconductor three-dimensional micro-nano structure 6 with internal stress.

[0080] The working principle of adjusting the band gap of the semiconductor three-dimensional micro-nano structure by controlling the cooling rate with the laser is as follows: by adjusting the height of the laser, the size of the laser spot can be changed. By adjusting the size of the laser spot, the heat treatment cooling rate of the optical fiber can be further controlled. The size of the laser spot determines the size of the area irradiated by the laser on the optical fiber. When other variables remain unchanged, the larger the spot size, the larger the area irradiated by the laser, and the smaller the temperature gradient of the heated part of the optical fiber, the slower the heat treatment cooling rate. Therefore, the cooling rate of the optical fiber can be adjusted according to different laser spot sizes. When the spot size is large, the cooling rate is slow, and when the spot size is small, the cooling rate is fast. At the same time, the glass transition temperature, density and thermal expansion coefficient of the silica cladding decrease with faster cooling rate, because the faster cooling rate reduces the time for liquid kinetic energy to be converted into heat energy, resulting in the structure of the liquid glass (cladding material) being solidified at a higher temperature. At an extremely fast cooling rate, the silica cladding still maintains the material properties at high temperature. At this time, the volume of the silica cladding is large, thereby further reducing the space for the micro-nano structure in the cladding and increasing the compressive stress of the semiconductor three-dimensional micro-nano structure.

[0081] Based on the principle, the method for producing and adjusting the band gap of the semiconductor three-dimensional micro-nano structure with the laser includes the following steps:

[0082] The semiconductor core optical fiber 5 is placed horizontally on the electric displacement table 3. First, low-power red light is emitted by the laser 1 for calibration to ensure that the laser beam is vertically irradiated on the center of the optical fiber. Then, the height of the laser is adjusted to change the size of the laser spot, which will affect the heat treatment cooling rate of the optical fiber, resulting in changes in the internal stress of the semiconductor three-dimensional micro-nano structure. The computer 4 controls the output power of the laser according to the melting point of the core to ensure that the core can be melted. At the same time, the computer 4 controls the electric displacement table 3 according to the required heating length and moving speed of the optical fiber to ensure that the optical fiber has sufficient heating time and temperature to form the semiconductor three-dimensional micro-nano structure 6. After the parameters are set, the laser emits laser, and the displacement table sends the optical fiber into the laser heating area at the set speed.

[0083] Preferably, the image captured by the camera before production is used to determine whether the heating area of the optical fiber has a solid-liquid alternating interface. If so, it indicates that the laser power and moving speed are appropriate. If not, the laser power and moving speed need to be adjusted. Specifically, the position and focal length of the camera 2 are adjusted, and when the heating area of the optical fiber has a solid-liquid alternating interface observed by the camera 2, it indicates that the appropriate laser power is reached, and a string of liquid droplets begins to form slowly. The image of this solid-liquid alternating interface not only shows the morphological changes of the optical fiber during heat treatment, but also can be used to accurately calculate the cooling rate of the optical fiber. By extracting the radiation intensity distribution in the picture, the temperature distribution can be quantified using the blackbody radiation principle, so as to draw the temperature distribution curve of the optical fiber during heat treatment and calculate the cooling rate. The blackbody radiation calculation formula is as follows:

[0084] ;

[0085] wherein, is the first radiation constant, is the second radiation constant. By accurately controlling the cooling rate, the internal stress and band gap size of the semiconductor three-dimensional micro-nano structure can be effectively adjusted.

[0086] As the optical fiber gradually moves away from the heating area, the spherical liquid droplets solidify to form solid semiconductor three-dimensional micro-nano structures 6.

[0087] Preferably, the compressive stress of the semiconductor is adjusted by changing the size of the laser spot alone, thereby affecting the band gap. The moving speed of the optical fiber is set to 10 . Under the condition of keeping the moving speed unchanged, laser beams with different spot diameters are used in turn, which are 1000 , 800 , 600 , and 400 . When changing the laser beams with different spot diameters, the laser power size also needs to be adjusted according to the melting point of the semiconductor core.

[0088] The Raman spectrum of the germanium semiconductor balls prepared by the parameters is shown in Figure 2 . Compared with the Raman peak of the germanium wafer, when the diameter of the laser spot is 1000 , 800 , 600 , and 400 , the Raman peaks of the germanium balls prepared by the parameters are shifted by 0 , 3.85 , 4.59 , and 5.33 , respectively.

[0089] For germanium material, the relationship between the first-order Raman peak shift and the pressure is:

[0090] ;

[0091] Here is the first derivative, i.e. and is the rate of change between them.

[0092] When the deformation does not exceed a certain elastic limit of the corresponding material, the relationship between stress and strain is:

[0093] ;

[0094] For germanium material, is the Young's modulus, taking 103GPa, is the stress, is the strain.

[0095] According to the calculation formula, the compressive stress of the above semiconductor germanium ball is 0, 0.99±0.07, 1.18±0.06 and 1.37±0.07 GPa respectively. The compressive strain is 0%, 0.96%±0.07%, 1.15%±0.06%, 1.33%±0.07% respectively.

[0096] Example 2: A method for adjusting the band gap of a semiconductor three-dimensional micro-nano structure by controlling the cooling rate of a tube furnace.

[0097] Based on the method described in Example 1, referring to FIG. 7, the method for adjusting the band gap of a semiconductor three-dimensional micro-nano structure by using a tube furnace in this example can include operations 7 to 9. Figure 3 In operation 7, the optical fiber is placed in the tube furnace. Since it is difficult to directly fix the optical fiber in the furnace, a high-temperature resistant glue is used to fix the optical fiber on a glass slide first to ensure its stability during the heating process.

[0098] In operation 8, the tube furnace is subjected to vacuum treatment. Since the semiconductor material is prone to react with oxygen to form an oxide at high temperatures, it is necessary to ensure a vacuum environment in the tube furnace to prevent oxidation of the semiconductor material.

[0099] In operation 9, the tube furnace program is set, including the temperature in the furnace, the holding time and the heating and cooling rate, all of which will affect the low-temperature recrystallization process of the semiconductor.

[0100]

[0101] ​wherein the temperature in the furnace is the recrystallization temperature of the semiconductor, which needs to be set below the melting point of the semiconductor material to ensure that the material will not melt. The holding time needs to be set sufficiently so that the semiconductor can be sufficiently affected by the thermal stress and allow enough time for the crystal to grow and rearrange. The cooling rate is the cooling rate of the optical fiber, which will affect the degree of crystallization of the semiconductor. Therefore, an appropriate cooling rate needs to be selected to ensure that the internal stress of the semiconductor three-dimensional micro-nano structure can still be preserved after cooling.

[0102] Preferably, the optical fiber prepared according to the method of Example 1 is transferred to a pure silica glass slide and fixed on the slide with a high-temperature resistant glue. Then, the slide with the optical fiber is placed in a tube furnace, and the inside of the tube furnace is first vacuumed. Subsequently, the tube furnace is set to heat at a specific heating rate, and heated to a reaction temperature of 200 above, and kept at this temperature for more than 1 hour. Then, it is cooled to room temperature at a cooling rate of less than 10 / min, which makes the semiconductor three-dimensional micro-nano structure undergo a low-temperature recrystallization process, and tensile stress is generated inside the semiconductor three-dimensional micro-nano structure, thereby further modifying the band gap of the semiconductor three-dimensional micro-nano structure.

[0103] The Raman spectrum of the semiconductor germanium ball prepared in Example 2 is shown in Figure 4 FIG. 6, compared with the Raman peaks of a germanium wafer and the semiconductor germanium ball prepared in Example 1. The Raman peak shift of the semiconductor germanium balls prepared in Example 1 and Example 2 is 3.73 , -2.63 , respectively (left shift is negative).

[0104] For germanium material, the amount of shift of the Raman peak is linearly related to the size of the tensile strain , and the calculation formula is:

[0105] ;

[0106] is a linear coefficient, which can be taken as -395 , for example.

[0107] According to the above calculation formula, the semiconductor germanium balls prepared in Example 1 and Example 2 can be converted into corresponding stress and strain. The stress size is 0.96±0.05 GPa of compressive stress and 0.69 GPa of tensile stress, respectively. The strain size is 0.93%±0.05% of compressive strain and 0.67% of tensile strain, respectively.

[0108] In order to characterize the effect of the applied stress on the band gap regulation of the semiconductor, Figure 5A comparison chart of photoluminescence spectra at room temperature of the semiconductor germanium spheres with compressive and tensile stress prepared in Example 1 and Example 2 is shown. As an indirect band gap semiconductor, the characteristic peak of the room temperature fluorescence spectrum of the semiconductor germanium spheres prepared in Example 1 and Example 2 is right-shifted with reference to the direct band gap energy 0.82 eV of the germanium wafer, indicating that the direct band gap energy is reduced under the stress. And under the action of compressive stress, the characteristic peak of the room temperature fluorescence spectrum of the semiconductor germanium spheres at 0.94 eV appears band gap splitting, forming a new fluorescence spectrum characteristic peak, enhancing the possibility of direct transition of electrons in germanium material, and even possibly inducing the transition of germanium material from an indirect band gap semiconductor to a direct band gap semiconductor.

[0109] It should be particularly pointed out that the semiconductor three-dimensional micro-nano structure after Example 1 is used in this embodiment in order to facilitate the comparison of semiconductor band gap characteristics and the subsequent preparation of semiconductor three-dimensional micro-nano structures. However, this embodiment is not limited to using the processed semiconductor three-dimensional micro-nano structure. The unprocessed semiconductor optical fiber can also achieve the purpose of adjusting the band gap by using this method.

[0110] Example 3: A preparation method of the band gap tunable semiconductor three-dimensional micro-nano structure obtains a band gap tunable, shape selectable and size controllable semiconductor three-dimensional micro-nano structure.

[0111] Example 3 takes a semiconductor core optical fiber with pure silicon as the core and silicon dioxide as the cladding as an example for illustration. Since hydrofluoric acid can corrode silicon dioxide, it is not easy to chemically react with the semiconductor. By corroding the cladding of the optical fiber with hydrofluoric acid, the cladding of the optical fiber can be effectively removed while the structural integrity of the semiconductor three-dimensional micro-nano structure is maintained. Then, by cleaning, the residual hydrofluoric acid and its reaction products are removed, thereby obtaining a group of independent semiconductor three-dimensional micro-nano structures with adjustable band gaps.

[0112] As shown in FIG. 4, it is an optical microscope image of an independent semiconductor silicon sphere. The diameter of the semiconductor sphere is about 126 Figure 6 . .

[0113] The semiconductor sphere is prepared by a silicon core optical fiber with a laser spot size of 1000 , a laser power of 25 W and a fiber moving speed of 5 .

[0114] The larger the diameter of the core is, the larger the size of the semiconductor three-dimensional micro-nano structure is. According to the requirements, different diameters of the core are selected, and the size of the semiconductor three-dimensional micro-nano structure prepared by the preparation method of Example 1 will be different. Since the spherical structure has high symmetry, the stress generated inside is more stable, and therefore the semiconductor sphere is more easily to achieve precise size control. The calculation formula of the diameter of the semiconductor sphere is as follows:

[0115] ;

[0116] D is the diameter size of the semiconductor sphere, Dc is the diameter size of the core, V is the moving speed of the optical fiber, is the viscosity size of the cladding at the heating temperature, is the interfacial tension between the cladding and the core at the heating temperature.

[0117] Therefore, the semiconductor three-dimensional micro-nano structure can realize adjustable band gap, optional shape and controllable size. By precisely controlling the size of the semiconductor three-dimensional micro-nano structure, the fine adjustment of the material performance can be realized, and the independent semiconductor three-dimensional micro-nano structure can be integrated in the electronic device in the state of maintaining stress, thereby meeting the diversified needs of different band gap semiconductor materials in various application fields.

[0118] It can be understood that the present application utilizes a laser to locally heat and process the optical fiber with a semiconductor as the core, and releases the semiconductor three-dimensional micro-nano structure from the optical fiber through tube furnace annealing. By controlling the cooling rate of the heating source, the present application realizes the band gap regulation of the semiconductor band gap structure by introducing different types and sizes of stress. The obtained semiconductor three-dimensional micro-nano structure can be used as an independent three-dimensional optical and acoustic element material, and is suitable for the construction of electronic devices.

[0119] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure, characterized in that, include: The semiconductor core optical fiber is heated to a target heating temperature, and the cooling rate during cooling is controlled. The heating process and cooling rate are related to the stress applied to the core and the three-dimensional semiconductor micro / nano structure within the optical fiber. The faster the cooling rate, the greater the stress. The stress can tune the bandgap of the three-dimensional semiconductor micro / nano structure. The semiconductor core optical fiber includes a core and a cladding. Specifically, when the target heating temperature is higher than the melting point of the fiber core, the optical fiber is locally heated to apply compressive stress to the fiber core and form a semiconductor three-dimensional micro / nano structure; when the target heating temperature is lower than the melting point of the fiber core, the optical fiber is heated as a whole to recrystallize the semiconductor three-dimensional micro / nano structure. By utilizing the volume difference between the recrystallized structure and the original structure, tensile stress is applied to the semiconductor three-dimensional micro / nano structure, and the bandgap structure is tuned. The process of heating the semiconductor core optical fiber to a target heating temperature and controlling the cooling rate during fiber cooling includes: heating the target area through a first heating source when the target heating temperature is higher than the melting point of the fiber core; during the heating process, various parts of the optical fiber enter and leave the target area at a target moving speed to form a semiconductor three-dimensional micro / nano structure in the fiber core; the target area and the optical fiber are located on the same horizontal plane; the target heating temperature is specifically the temperature at the center of the target area, which is higher than the melting point of the fiber core; the optical fiber has a first cooling rate during the process of leaving the target area; during the cooling process, due to the anomalous expansion characteristics of the fiber core, its volume begins to increase, thereby being restricted and compressed by the surrounding cladding; this volume mismatch causes compressive stress to be generated inside the semiconductor core material. The process of heating the semiconductor core optical fiber to a target heating temperature and controlling the cooling rate during fiber cooling further includes: heating the optical fiber treated by the first heating source using a second heating source when the target heating temperature is lower than the melting point of the fiber core, so as to recrystallize the three-dimensional micro / nano structure of the semiconductor in the optical fiber. The target heating temperature provided by the second heating source to the optical fiber is lower than the melting point of the fiber core. The overall heating process includes a heating stage from a preset temperature to the target heating temperature, a holding stage, and a cooling stage from the target heating temperature to the preset temperature. The cooling stage has a second cooling rate. During the heating and cooling process, due to the distribution of the temperature gradient, the semiconductor core crystal begins to recrystallize. During the crystal growth process, new crystal orientations gradually form, internal defects are eliminated or reduced, and the internal structure begins to rearrange, forming a more compact and ordered crystal structure, thereby reducing the crystal volume. As the volume of the semiconductor core material shrinks, the cladding material hardly expands or contracts, and its volume change is small. This volume mismatch causes tensile stress to be generated inside the semiconductor core material.

2. The method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure according to claim 1, characterized in that, When the target area is uniformly heated by the first heating source, the shape of the semiconductor three-dimensional micro / nano structure is spherical; When the target area is heated non-uniformly by the first heating source, the shape of the semiconductor three-dimensional micro / nano structure is non-spherical.

3. The method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure according to claim 1, characterized in that, The first heating source is a laser, and before heating the target area using the first heating source, the system also includes: Adjust the height of the laser to determine the size of the laser spot formed in the target area. The size of the spot affects the cooling rate; the smaller the spot size, the faster the initial cooling rate.

4. The method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure according to claim 3, characterized in that, Also includes: Acquire images of the optical fibers in the target area; The image is displayed and the target input is received. The image is used to calculate and quantify the cooling rate using the blackbody radiation principle. The target input is used to indicate the adjustment amount of the moving speed and the adjustment amount of the laser output power. In response to the target input, the target moving speed of the optical fiber and the output power of the laser are controlled based on the adjustment amount of the moving speed and the adjustment amount of the output power.

5. The method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure according to claim 1, characterized in that, Also includes: The optical fiber is carried by a displacement stage, which is used to move the optical fiber at the target moving speed during the process of heating the target area by a first heating source.

6. The method for fabricating a bandgap-tunable three-dimensional semiconductor micro / nano structure according to claim 1, characterized in that, The second heating source is a tubular furnace; The tube furnace is used to carry optical fibers containing semiconductor three-dimensional micro-nano structures after being treated by a first heating source, and to adjust the furnace temperature in a vacuum environment according to the target furnace temperature, heating rate, cooling rate and holding time. The target furnace temperature is the target heating temperature and the cooling rate is the second cooling rate.

7. A semiconductor three-dimensional micro / nano structure, characterized in that, The semiconductor three-dimensional micro / nano structure is prepared using the method for preparing a bandgap tunable semiconductor three-dimensional micro / nano structure as described in any one of claims 1-6.

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