Semiconductor quantum well structure and preparation method thereof

Abstract

The present disclosure provides a method for preparing a semiconductor quantum well structure, comprising: forming an n-type semiconductor layer on one side of a substrate; forming a multi-quantum well structure on the side of the n-type semiconductor layer facing away from the substrate, the multi-quantum well structure comprising quantum barrier layers and quantum well layers that are alternately arranged, the material of the quantum well layer comprising: indium gallium nitride, the quantum barrier layer comprising: a barrier layer base layer and a barrier layer modulation layer located on the side of the barrier layer base layer facing away from the substrate, the barrier layer modulation layer comprising a plurality of first raised stripes that are periodically arranged along a preset first direction, the quantum well layer comprising: a well layer base layer and a well layer modulation layer located on the side of the well layer base layer facing away from the substrate, the well layer modulation layer comprising a plurality of second raised stripes that are periodically arranged along a preset second direction, one of the preset first direction and the preset second direction being a circumferential direction of the substrate, and the other being a radial direction of the substrate; forming a p-type semiconductor layer on the side of the multi-quantum well structure facing away from the substrate.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductor technology, and in particular to a semiconductor quantum well structure and a preparation method thereof. Background Art

[0002] Gallium nitride semiconductor light-emitting diodes and lasers have the advantages of small size, high efficiency, long life, and fast response rate. They have great application prospects in the fields of biology, medicine, communications, display, lighting, etc. As the active layer to improve the electro-optical conversion efficiency of gallium nitride optoelectronic devices, the structure and growth quality of InGaN / GaN multi-quantum wells are very important to the performance of the device. In recent years, the emission wavelength range of gallium nitride light-emitting devices has gradually increased, from blue light to green light, and even to the yellow light region. The corresponding InGaN / GaN multi-quantum wells require a higher indium component.

[0003] InGaN / GaN multiple quantum wells with high indium content bring certain challenges to the performance indicators and preparation process of the device. On the one hand, the mismatch stress between the InGaN well layer and the GaN barrier layer increases with the increase of indium content, resulting in a large piezoelectric polarization field in the well layer, generating a quantum confined Stark effect (QCSE), which causes the quantum well band bending. The QCSE effect separates the electron and hole wave functions in the quantum well space, greatly reducing the radiation recombination efficiency and causing the device's emission wavelength to drift. On the other hand, the increase of indium content will also cause phase separation in the InGaN well layer, making the indium component unevenly distributed in the well layer. Summary of the invention

[0004] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and proposes a semiconductor quantum well structure and a preparation method thereof.

[0005] In a first aspect, an embodiment of the present disclosure provides a method for preparing a semiconductor quantum well structure, comprising:

[0006] forming an n-type semiconductor layer on one side of the substrate;

[0007] A multi-quantum well structure is formed on a side of the n-type semiconductor layer facing away from the substrate, the multi-quantum well structure includes quantum barrier layers and quantum well layers that are alternately arranged, the material of the quantum well layer includes: indium gallium nitride, the quantum barrier layer includes: a barrier layer base layer and a barrier layer modulation layer located on the side of the barrier layer base layer facing away from the substrate, the barrier layer modulation layer includes a plurality of first raised stripes that are periodically arranged along a preset first direction, the quantum well layer includes: a well layer base layer and a well layer modulation layer located on the side of the well layer base layer facing away from the substrate, the well layer modulation layer includes a plurality of second raised stripes that are periodically arranged along a preset second direction, one of the preset first direction and the preset second direction is a circumferential direction of the substrate, and the other is a radial direction of the substrate;

[0008] A p-type semiconductor layer is formed on the side of the multi-quantum well structure facing away from the substrate.

[0009] In some embodiments, the step of forming a multi-quantum well structure on a side of the n-type semiconductor layer facing away from the substrate comprises: alternately performing the steps of forming a quantum barrier layer and forming a quantum well layer;

[0010] The steps of forming the quantum barrier layer include:

[0011] The step of generating a barrier layer base layer: generating a barrier layer material film on a first intermediate product structure to obtain a barrier layer base layer, wherein the first intermediate product structure at least includes the substrate and the n-type semiconductor layer;

[0012] The step of generating a barrier layer modulation layer: continuously growing a barrier layer material on the barrier layer base layer, and simultaneously controlling the substrate to rotate at a first rotation speed and controlling a light spot of a first polarized pulsed laser to move from the center of the surface of the barrier layer base layer along a preset straight line pointing direction toward the edge of the surface of the barrier layer base layer at a first linear motion speed, so as to induce the formation of a first raised stripe, thereby obtaining a barrier layer modulation layer;

[0013] The steps of forming a quantum well layer include:

[0014] The step of generating a well layer base layer: growing a well layer material film on a second intermediate product structure to obtain a well layer base layer, wherein the second intermediate product structure at least includes the substrate, the n-type semiconductor layer and at least one quantum barrier layer;

[0015] The step of generating a well layer modulation layer: continuously growing a well layer material on the barrier layer base layer, and simultaneously controlling the substrate to rotate at a second rotation speed and controlling the light spot of a second polarized pulsed laser to move from the center of the surface of the well layer base layer along the preset straight line pointing direction toward the edge of the surface of the well layer base layer at a second linear motion speed, so as to induce the formation of a second raised stripe, thereby obtaining a well layer modulation layer;

[0016] Among them, one of the first polarized pulse laser and the second polarized pulse laser is an S-polarized pulse laser, and the other is a P-polarized pulse laser.

[0017] In some embodiments, the first rotation speed is N1 rpm, the diameter of the spot of the first polarized pulsed laser is D1 mm, and the first linear motion speed is V1 mm / min, wherein N1, D1 and V1 satisfy: V1=D1 / N1;

[0018] And / or, the second rotation speed is N2 rpm, the diameter of the spot of the second polarized pulse laser is D2 mm, and the second linear motion speed is V2 mm / min, wherein N2, D2 and V2 satisfy: V2=D2 / N2.

[0019] In some embodiments, the energy of a single photon of the first polarized pulsed laser is 0.95 to 1.05 times the energy band gap of the barrier layer base layer material, and the energy density per unit area of ​​the first polarized pulsed laser is lower than the ablation threshold of the barrier layer base layer material;

[0020] And / or, the energy of a single photon of the second polarized pulse laser is 0.95 to 1.05 times the energy band gap of the well layer base layer material, and the energy density per unit area of ​​the second polarized pulse laser is lower than the ablation threshold of the well layer base layer material.

[0021] In some embodiments, the step of forming a multi-quantum well structure on a side of the n-type semiconductor layer facing away from the substrate is implemented based on a thin film deposition device, the thin film deposition device comprising: a polarization pulse laser device, a reaction chamber, a tray and a dimming window, the tray is located in the reaction chamber and can rotate, the polarization pulse laser device is arranged outside the reaction chamber, the dimming window is located at the top of the reaction chamber, the polarization pulse laser device is configured to emit a P-polarization pulse laser or an S-polarization pulse laser toward the dimming window, and the dimming window is configured to adjust the light emission direction of the incident P-polarization pulse laser or S-polarization pulse laser;

[0022] The step of generating a barrier layer base layer specifically includes: controlling a tray carrying a first intermediate product structure to rotate, introducing a barrier layer growth gas into the reaction chamber, and controlling a polarized pulse laser device not to output a pulse laser, so as to generate a barrier layer material film on the first intermediate product to obtain a barrier layer base layer;

[0023] The step of generating a barrier layer modulation layer comprises: controlling a tray carrying a first intermediate product structure to rotate at a first rotation speed, controlling a polarization pulse laser device to output a first polarization pulse laser, and controlling the light emitting direction of the first polarization pulse laser through a dimming window so that a light spot of the first polarization pulse laser moves from the center of the surface of the barrier layer base layer along a preset straight line pointing direction toward the edge of the surface of the barrier layer base layer at a first linear motion speed, so as to induce the formation of a first raised stripe, thereby obtaining a barrier layer modulation layer;

[0024] The step of generating the well layer foundation layer specifically includes: controlling the tray carrying the second intermediate product structure to rotate, introducing a well layer growth gas into the reaction chamber, and controlling the polarization pulse laser device not to output pulse laser, so as to generate a well layer material film on the second intermediate product to obtain the well layer foundation layer;

[0025] The steps of generating a well layer modulation layer include: controlling a tray carrying a second intermediate product structure to rotate at a second rotation speed, controlling a polarization pulse laser device to output a second polarization pulse laser, and controlling the light emitting direction of the first polarization pulse laser through a dimming window so that the light spot of the first polarization pulse laser moves from the center of the surface of the well layer base layer along a preset straight line pointing direction toward the edge of the surface of the well layer base layer at a second linear motion speed to induce formation of a second raised stripe to obtain a well layer modulation layer.

[0026] In some embodiments, the polarization pulse laser device comprises:

[0027] a pulse laser source configured to generate pulse laser light;

[0028] A filter lens configured to convert the pulsed laser output by the pulsed laser source into linearly polarized light;

[0029] A beam splitter prism configured to transmit a portion of the linearly polarized light emitted from the filter lens to obtain an S-polarized pulse laser, and reflect another portion to obtain a P-polarized pulse laser;

[0030] The S-polarized pulse laser transmission control optical path has an on state and an off state, and is configured to enable the S-polarized pulse laser emitted from the beam splitter prism to be transmitted to the intermediate light-guiding reflective prism through the S-polarized pulse laser transmission control optical path when in the on state, and to prevent the S-polarized pulse laser emitted from the beam splitter prism from being transmitted to the intermediate light-guiding reflective prism when in the off state;

[0031] A P-polarized pulse laser transmission control optical path, having an on state and an off state, and configured to enable the P-polarized pulse laser emitted from the beam splitter prism to be transmitted to the intermediate light-guiding reflective prism through the P-polarized pulse laser transmission control optical path when in the on state, and to prevent the P-polarized pulse laser emitted from the beam splitter prism from being transmitted to the intermediate light-guiding reflective prism when in the off state;

[0032] The intermediate light-guiding reflecting prism is configured to direct the input S-polarized pulse laser or P-polarized pulse laser toward the dimming window by the principle of reflection.

[0033] In some embodiments, the step of controlling the polarization pulse laser device not to output pulse laser specifically includes: controlling the S-polarization pulse laser transmission control optical path and the P-polarization pulse laser transmission control optical path to be in a closed state;

[0034] When the first polarized pulse laser is an S polarized pulse laser and the second polarized pulse laser is a P polarized pulse laser, the step of controlling the polarized pulse laser device to output the first polarized pulse laser specifically includes: controlling the S polarized pulse laser transmission control optical path to be in an open state and controlling the P polarized pulse laser transmission control optical path to be in a closed state, and the step of controlling the polarized pulse laser device to output the second polarized pulse laser specifically includes: controlling the S polarized pulse laser transmission control optical path to be in a closed state and controlling the P polarized pulse laser transmission control optical path to be in an open state;

[0035] When the first polarization pulse laser is a P polarization pulse laser and the second polarization pulse laser is an S polarization pulse laser, the step of controlling the polarization pulse laser device to output the first polarization pulse laser specifically includes: controlling the P polarization pulse laser transmission control optical path to be in an open state and controlling the S polarization pulse laser transmission control optical path to be in a closed state, and the step of controlling the polarization pulse laser device to output the second polarization pulse laser specifically includes: controlling the P polarization pulse laser transmission control optical path to be in a closed state and controlling the S polarization pulse laser transmission control optical path to be in an open state.

[0036] In some embodiments, the dimming window is an electrically controlled birefringent optical crystal window.

[0037] In some embodiments, the thickness of the barrier base layer is 1 to 10 nm, and the thickness of the barrier modulation layer is 2 to 10 nm;

[0038] The thickness of the well layer foundation layer is 1-10 nm, and the thickness of the well layer modulation layer is 2-10 nm.

[0039] In a second aspect, an embodiment of the present disclosure provides a semiconductor quantum well structure, which is prepared using the preparation method provided in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a cross-sectional schematic diagram of a semiconductor quantum well structure involved in the present disclosure.

[0041] Figure 2 A flow chart of a method for preparing a semiconductor quantum well structure provided in an embodiment of the present disclosure.

[0042] Figure 3 A schematic diagram of the structure of periodic raised stripes modulated by S-polarized pulse laser and P-polarized pulse laser in the present disclosure.

[0043] Figure 4 Scanning electron micrographs of periodic raised stripes modulated by S-polarized pulsed laser and P-polarized pulsed laser in the present disclosure.

[0044] Figure 5 It is a schematic diagram of the structure of a thin film deposition device involved in an embodiment of the present disclosure.

[0045] Figure 6 A flow chart of a method for preparing a semiconductor quantum well structure provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0047] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, similar words such as "one", "one" or "the" do not indicate quantity restrictions, but indicate that there is at least one. Similar words such as "include" or "comprise" mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Similar words such as "connect" or "connected" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described target changes, the relative positional relationship may also change accordingly.

[0048] In each of the accompanying drawings, identical elements are represented by similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not all drawn to scale. In addition, some well-known parts may not be shown in the drawings.

[0049] Many specific details of the present disclosure are described below, such as component structures, materials, dimensions, processing techniques, and technologies, in order to more clearly understand the present disclosure. However, as those skilled in the art will appreciate, the present disclosure may be implemented without following these specific details.

[0050] Figure 1 Schematic diagram of a cross-section of a semiconductor quantum well structure involved in the present disclosure. Figure 1 As shown, the semiconductor quantum well structure in the present disclosure includes, from bottom to top, an n-type semiconductor layer, a multi-quantum well structure, and a p-type semiconductor layer. The multi-quantum well structure includes: quantum barrier layers and quantum well layers arranged alternately.

[0051] The quantum barrier layer material has a wide band gap. The quantum barrier layer is located between adjacent quantum well layers, forming a potential barrier between the quantum well layers. These potential barriers block the escape of electrons and holes, thereby enhancing the carrier confinement effect in the quantum well. The thickness of the quantum barrier layer (also called the potential barrier layer) has an important influence on the performance of the multiple quantum wells. Increasing the thickness of the quantum barrier layer can suppress the coupling of wave functions between adjacent quantum well layers and further regulate the luminescence characteristics of MQWs. Conversely, reducing the thickness of the quantum barrier layer will lead to enhanced coupling between adjacent quantum well layers, affecting the optoelectronic performance of the device.

[0052] The quantum well layer material has a narrow band gap, and the main function of the quantum well layer is to limit the movement of electrons and holes in a specific dimension. This confinement effect leads to the phenomenon of quantum confinement, which makes the energy levels of electrons and holes discrete and forms a bound potential well. The thickness and composition of the quantum well layer have an important influence on the optical and electrical properties of the quantum well; by adjusting the width and composition of the well layer, the band structure can be precisely controlled, thereby optimizing the performance of optoelectronic devices. In applications such as green LEDs, the quantum well layer in the InGaN multi-quantum well structure has a high In content, which helps to achieve light emission of a specific wavelength.

[0053] In the present disclosure, the quantum barrier layer includes: a barrier layer base layer and a barrier layer modulation layer located on the barrier layer base layer, the barrier layer base layer and the barrier layer modulation layer are made of the same material, and the barrier layer modulation layer includes a plurality of first raised stripes periodically arranged along a preset first direction. Optionally, the material of the quantum barrier layer includes: gallium nitride or indium gallium nitride.

[0054] The quantum well layer includes: a well layer base layer and a well layer modulation layer located on the well layer base layer, the well layer base layer and the well layer modulation layer are made of the same material, and the well layer modulation layer includes a plurality of second raised stripes periodically arranged along a preset second direction. One of the preset first direction and the preset second direction is a circumferential direction of the substrate, and the other is a radial direction of the substrate. Optionally, the material of the quantum well layer includes: indium gallium nitride.

[0055] It should be noted that when the material of the quantum barrier layer includes InGaN, the indium doping amount of the InGaN material in the quantum barrier layer is smaller than the indium doping amount of the InGaN material in the quantum well layer.

[0056] In some embodiments, a barrier layer is further disposed between the multi-quantum well structure and the p-type semiconductor layer. The material of the barrier layer may be the same as that of the quantum barrier layer. The barrier layer is a non-essential functional structural layer.

[0057] Figure 2 A flow chart of a method for preparing a semiconductor quantum well structure provided by an embodiment of the present disclosure. Figure 2 As shown, the preparation method can be used to prepare Figure 1 The semiconductor quantum well structure shown in FIG. 1 , the preparation method comprises:

[0058] Step S1, forming an n-type semiconductor layer on one side of a substrate.

[0059] Step S2, forming a multi-quantum well structure on the side of the n-type semiconductor layer facing away from the substrate, the multi-quantum well structure includes quantum barrier layers and quantum well layers that are alternately arranged, the material of the quantum barrier layer includes: indium gallium nitride, the quantum barrier layer includes: a barrier layer base layer and a barrier layer modulation layer located on the side of the barrier layer base layer facing away from the substrate, the barrier layer modulation layer includes a plurality of first raised stripes periodically arranged along a preset first direction, the quantum well layer includes: a well layer base layer and a well layer modulation layer located on the side of the well layer base layer facing away from the substrate, the well layer modulation layer includes a plurality of second raised stripes periodically arranged along a preset second direction, one of the preset first direction and the preset second direction is a circumferential direction of the substrate, and the other is a radial direction of the substrate.

[0060] In the present disclosure, the number of quantum barrier layers and quantum well layers can be designed and modulated accordingly according to actual needs.

[0061] Step S3: forming a p-type semiconductor layer on the side of the multi-quantum well structure facing away from the substrate.

[0062] In the present disclosure, a plurality of first raised stripes periodically arranged along a preset first direction on the barrier layer modulation layer can form a first deformation relaxation structure similar to a bellows, a spring, etc. having deformation relaxation capability, and the stress relaxation direction of the first deformation relaxation structure is the preset first direction. Correspondingly, a plurality of second raised stripes periodically arranged along a preset second direction on the barrier layer modulation layer can also form a second deformation relaxation structure having deformation relaxation capability, and the stress relaxation direction of the second deformation relaxation structure is the preset second direction. The above-mentioned first deformation relaxation structure and second deformation relaxation structure can effectively relax the stress and strain between the quantum barrier layer and the quantum well layer, reduce the piezoelectric polarization field, thereby reducing the quantum confined Stark effect, and improve the efficiency of radiation recombination under high indium components. The preparation process of the entire multi-quantum well structure does not require the introduction of other strain-regulated growth materials, nor does it require the design of a complex quantum well structure.

[0063] In addition, since one of the preset first direction and the preset second direction is the circumferential direction of the substrate, and the other is the radial direction of the substrate, the stress relaxation directions of the first deformation relaxation structure and the second deformation relaxation structure whose orthographic projections on the substrate are located in the same area are perpendicular (can be regarded as two different bellows stacked vertically), and the stress release of the first deformation relaxation structure and the stress release of the second deformation relaxation structure are relatively independent, and the stress strain will not interfere with each other or only have very little interference.

[0064] In addition, the periodic arrangement of the first raised stripes in the quantum barrier layer can also effectively inhibit the enrichment of indium during the subsequent growth of the quantum well layer, and improve the uniformity of the distribution of the indium component in the quantum well layer (when the material of the quantum well layer is also doped with indium, the periodic arrangement of the second raised stripes in the quantum well layer can also effectively inhibit the enrichment of indium during the subsequent growth of the quantum barrier layer, and improve the uniformity of the distribution of the indium component in the quantum barrier layer).

[0065] In addition, the periodic multiple first / second raised stripes form a corrugated structure, which can effectively reduce the overall thickness of the multi-quantum well structure formed by the quantum barrier layer + quantum well layer while ensuring the effective thickness of the quantum barrier layer / well layer film (the portion on the quantum well layer will fill the gaps between the first raised stripes, and the portion on the quantum barrier layer will fill the gaps between the second raised stripes).

[0066] In some embodiments, the thickness of the barrier layer base layer is 1-10 nm, and the thickness of the barrier layer modulation layer is 2-10 nm; the thickness of the well layer base layer is 1-10 nm, and the thickness of the well layer modulation layer is 2-10 nm.

[0067] In some embodiments, step S2 includes: alternately performing step S201 of forming a quantum barrier layer and step S202 of forming a quantum well layer.

[0068] The step S201 of forming a quantum barrier layer includes: a step S2011 of generating a barrier layer base layer and a step S2012 of generating a barrier layer modulation layer. The step of generating a barrier layer base layer specifically includes: generating a barrier layer material film on a first intermediate product structure to obtain a barrier layer base layer, the first intermediate product structure at least includes a substrate and an n-type semiconductor layer; the step of generating a barrier layer modulation layer includes: continuously growing a barrier layer material on the barrier layer base layer, and simultaneously controlling the substrate to rotate at a first rotation speed and controlling the light spot of a first polarized pulsed laser to move from the center of the surface of the barrier layer base layer along a preset straight line pointing direction toward the edge of the surface of the barrier layer base layer at a first linear motion speed, so as to induce the formation of a first raised stripe to obtain a barrier layer modulation layer.

[0069] The step S202 of forming a quantum well layer includes: a step S2021 of generating a well layer base layer and a step S2022 of generating a well layer modulation layer. The step of generating the well layer base layer specifically includes: growing a well layer material film on the second intermediate product structure to obtain the well layer base layer, the second intermediate product structure at least includes a substrate, an n-type semiconductor layer and at least one quantum barrier layer; the step of generating the well layer modulation layer specifically includes: continuously growing the well layer material on the barrier layer base layer, and simultaneously controlling the substrate to rotate at a second rotation speed and controlling the light spot of the second polarized pulsed laser to move from the center of the surface of the well layer base layer along a preset straight line pointing direction toward the edge of the surface of the well layer base layer at a second linear motion speed, so as to induce the formation of a second raised stripe to obtain the well layer modulation layer;

[0070] In the above steps S201 and S202, one of the first polarized pulsed laser and the second polarized pulsed laser is an S polarized pulsed laser, and the other is a P polarized pulsed laser. The S polarized laser refers to a laser whose electric vector (polarization direction) is perpendicular to the incident plane, and the P polarized laser refers to a laser whose electric vector (polarization direction) is parallel to the incident plane.

[0071] Figure 3 A schematic diagram of the structure of periodic raised stripes modulated by S-polarized pulse laser and P-polarized pulse laser in the present disclosure. Figure 4 The scanning electron micrographs of the periodic raised stripes modulated by the S-polarized pulse laser and the P-polarized pulse laser in the present disclosure are shown in FIG. Figure 3 and Figure 4As shown, the principle of using pulsed laser to modulate semiconductor materials to form periodic raised stripes in the present disclosure is as follows: the interaction between light and matter is not only an important detection method for exploring the microscopic physical mechanism of low-dimensional quantum materials, but also ultra-short and ultra-strong pulsed lasers can be used as effective modulation methods for electronic structure and physical state. In crystals, the periodic arrangement of atoms in real space constitutes the crystal structure and thus causes the energy band structure of electrons to be periodic in momentum space; by analogy, the external periodic oscillation potential field will also cause the periodic replication of the energy band structure of electrons in energy space, thereby forming a Floquet State. Further, through the interaction between electrons and periodic potential fields, the energy band structure, symmetry and topological properties of low-dimensional quantum materials can be instantaneously regulated, and new physical states that are not in equilibrium can be achieved, for example, converting topologically mediocre materials into topological materials, and realizing topological superconducting states far from equilibrium states. The above-mentioned quantum physical state regulation mechanism driven by periodic fields is called Floquet engineering. In addition, when Ozkan et al. irradiated diamond with pulsed laser (Ozkan et al., Femtosecond laser-induced periodic structure writing on diamond crystals and microclusters, Applied Physics Letters, 1999, 75, 3716-3718), they found that periodic stripes could be observed in the laser irradiated area on the surface of single crystal and polycrystalline diamond. This type of periodic stripe structure was later called laser-induced periodic surface structures (LIPSS for short). This is a periodic stripe structure induced on the surface of the material by laser irradiation, which can change the optical, mechanical and chemical properties of the material. The formation of LIPSS is affected by irradiation conditions, environmental media and materials. Whether the surface of the surface periodic structure is smooth or not is determined by the energy density of the incident laser. See Figure 3 and Figure 4 In part (a), when the incident laser is S-polarized (the polarization direction is perpendicular to the incident plane), the extension direction of the periodic fringes is perpendicular to the polarization direction of the laser, and the arrangement direction of the periodic fringes is perpendicular to the extension direction of the periodic fringes; see Figure 3 and Figure 4In part (b), when the incident laser is P-polarized (the polarization direction is parallel to the incident plane), the extension direction of the periodic stripes is perpendicular to the polarization direction of the laser, and the arrangement direction of the periodic stripes is perpendicular to the extension direction of the periodic stripes. The present disclosure is based on the above principle, and by controlling the laser irradiation parameters, smooth periodic raised stripes are formed on the surface of the semiconductor material. Indium forms a certain modulation distribution under the local potential field, and the density and structure of the periodic raised stripes can be controlled by changing the laser wavelength. Since the polarization directions of the S-polarized pulse laser and the P-polarized pulse laser are perpendicular to each other, the S-polarized pulse laser and the P-polarized pulse laser can be used to form spatially vertical periodic raised stripes on the quantum barrier layer and the quantum well layer. For example, an S-polarized pulsed laser can be used to form periodic raised stripes along the radial direction of the epitaxial surface on the quantum barrier layer (or quantum well layer), and a P-polarized pulsed laser can be used to form periodic raised stripes along the circumferential direction of the epitaxial surface on the quantum well layer (or quantum barrier layer). That is, the periodic raised stripes on the quantum barrier layer and the quantum well layer are nearly perpendicular to each other in spatial projection, thereby reducing and relaxing the stress and strain between the quantum well barrier layer and the quantum well layer.

[0072] In some embodiments, the first rotation speed is N1 rpm, the diameter of the spot of the first polarized pulse laser is D1 mm, and the first linear motion speed is V1 mm / min, wherein N1, D1 and V1 satisfy: V1 = D1 / N1. With such a design, the first polarized pulse laser can quickly perform full coverage scanning on the surface of the entire intermediate product structure.

[0073] In some embodiments, the second rotation speed is N2 rpm, the diameter of the spot of the second polarized pulse laser is D2 mm, and the second linear motion speed is V2 mm / min, wherein N2, D2 and V2 satisfy: V2 = D2 / N2. With such a design, the first polarized pulse laser can quickly perform full coverage scanning on the surface of the entire intermediate product structure.

[0074] In some embodiments, the energy of a single photon of the first polarized pulsed laser is 0.95 to 1.05 times the energy bandgap of the barrier layer base layer material, and the energy density per unit area of ​​the first polarized pulsed laser is lower than the ablation threshold of the barrier layer base layer material. The energy of a single photon of the second polarized pulsed laser is 0.95 to 1.05 times the energy bandgap of the well layer base layer material, and the energy density per unit area of ​​the second polarized pulsed laser is lower than the ablation threshold of the well layer base layer material. This design is to ensure that the polarized pulsed laser can effectively modulate the surface of the quantum well layer / barrier layer while avoiding laser burning of the quantum well layer / barrier layer.

[0075] Figure 5 FIG. 1 is a schematic diagram of the structure of a thin film deposition device involved in an embodiment of the present disclosure. Figure 5As shown, in some embodiments, the step S2 of forming the multi-quantum well structure is implemented based on a thin film deposition device. The thin film deposition device includes: a polarization pulse laser device 200, a reaction chamber 100, a tray 104 (e.g., a graphite tray) and a dimming window 112, wherein the tray 104 is located in the reaction chamber 100 and can rotate, the polarization pulse laser device 200 is arranged outside the reaction chamber 100, the dimming window 112 is located at the top of the reaction chamber 100, the polarization pulse laser device 200 is configured to emit a P-polarized pulse laser or an S-polarized pulse laser toward the dimming window 112, and the dimming window 112 is configured to adjust the light emission direction of the incident P-polarized pulse laser or S-polarized pulse laser to modulate the position of the laser spot on the structure to be processed.

[0076] The reaction chamber 100 is provided with reaction source gas inlets 106 and 107 for inputting reaction gas into the reaction chamber 100 and an exhaust gas outlet 108 for discharging gas in the reaction chamber 100. Optionally, the exhaust gas outlet 108 is substantially flush with the tray, and the height of the exhaust gas outlet 108 is lower than the height of the reaction source gas inlets 106 and 107, so that the reaction gas can be gathered at the tray as much as possible, which is conducive to improving the process efficiency.

[0077] The step S2011 of generating a barrier layer base layer specifically includes: controlling the tray 104 carrying the first intermediate product structure to rotate, introducing barrier layer growth gas into the reaction chamber 100, and controlling the polarization pulse laser device 200 not to output pulse laser, so as to generate a barrier layer material film on the first intermediate product to obtain a barrier layer base layer.

[0078] The step S2012 of generating a barrier layer modulation layer includes: controlling the tray 104 carrying the first intermediate product structure to rotate at a first rotation speed, controlling the polarization pulse laser device 200 to output a first polarization pulse laser, and controlling the light emitting direction of the first polarization pulse laser through the dimming window 112 so that the light spot of the first polarization pulse laser moves from the center of the surface of the barrier layer base layer along a preset straight line pointing direction toward the edge of the surface of the barrier layer base layer at a first linear motion speed, so as to induce the formation of a first raised stripe to obtain a barrier layer modulation layer.

[0079] The step S2021 of generating a well layer foundation layer specifically includes: controlling the tray 104 carrying the second intermediate product structure to rotate, introducing a well layer growth gas into the reaction chamber 100, and controlling the polarization pulse laser device 200 not to output a pulse laser, so as to generate a well layer material film on the second intermediate product to obtain a well layer foundation layer;

[0080] The step S2022 of generating a well layer modulation layer includes: controlling the tray 104 carrying the second intermediate product structure to rotate at a second rotation speed, controlling the polarization pulse laser device 200 to output a second polarization pulse laser, and controlling the light emitting direction of the first polarization pulse laser through the dimming window 112 so that the light spot of the first polarization pulse laser moves from the center of the surface of the well layer base layer along a preset straight line pointing direction toward the edge of the surface of the well layer base layer at a second linear motion speed, so as to induce the formation of a second raised stripe to obtain a well layer modulation layer.

[0081] In the present disclosure, the rotational motion of the substrate 105 is combined with the linear motion of the pulsed laser spot to achieve effective scanning of the quantum well layer and the quantum barrier layer by the pulsed laser spot.

[0082] See also Figure 5 As shown, in some embodiments, the polarization pulse laser device includes: a pulse laser source 201, a filter lens 202, a beam splitter prism 203, an S-polarized pulse laser transmission control optical path, a P-polarized pulse laser transmission control optical path and an intermediate light-guiding reflecting prism.

[0083] The pulse laser source 201 is configured to generate pulse laser.

[0084] The filter lens 202 is configured to convert the pulsed laser light outputted by the pulsed laser source into linearly polarized light.

[0085] The beam splitter prism 203 is configured to transmit a portion of the linearly polarized light emitted from the filter lens to obtain S-polarized pulsed laser light, and reflect the other portion to obtain P-polarized pulsed laser light.

[0086] The S-polarized pulse laser transmission control optical path has an on state and a off state, and is configured to enable the S-polarized pulse laser emitted from the beam splitter prism 203 to be transmitted to the intermediate light-guiding reflecting prism through the S-polarized pulse laser transmission control optical path when in the on state, and to prevent the S-polarized pulse laser emitted from the beam splitter prism 203 from being transmitted to the intermediate light-guiding reflecting prism when in the off state.

[0087] The P-polarized pulse laser transmission control optical path has an on state and a off state, and is configured to enable the P-polarized pulse laser emitted from the beam splitter prism 203 to be transmitted to the intermediate light-guiding reflecting prism through the P-polarized pulse laser transmission control optical path when in the on state, and to prevent the P-polarized pulse laser emitted from the beam splitter prism 203 from being transmitted to the intermediate light-guiding reflecting prism when in the off state.

[0088] The intermediate light-guiding reflecting prism is configured to be able to direct the input S-polarized pulsed laser or P-polarized pulsed laser toward the dimming window 112 through the reflection principle. The intermediate light-guiding reflecting prism includes a plurality of reflecting mirrors 207, 208, 209 arranged according to actual needs.

[0089] In some embodiments, the S-polarized pulsed laser transmission control optical path includes an S-polarized pulsed laser source filter 205 ; in some embodiments, the P-polarized pulsed laser transmission control optical path includes a P-polarized pulsed laser source filter 206 and a reflecting prism 204 .

[0090] In practical applications, the S / P polarized pulse laser source filters 205 , 206 may be rotated to control the S / P polarized pulse laser to pass through or not pass through the S / P polarized pulse laser source filters 205 , 206 .

[0091] In some embodiments, the step of controlling the polarized pulse laser device 200 not to output pulsed laser specifically includes: controlling both the S-polarized pulse laser transmission control optical path and the P-polarized pulse laser transmission control optical path to be in a closed state.

[0092] When the first polarization pulse laser is an S-polarization pulse laser and the second polarization pulse laser is a P-polarization pulse laser, the step of controlling the polarization pulse laser device to output the first polarization pulse laser specifically includes: controlling the S-polarization pulse laser transmission control optical path to be in an open state and controlling the P-polarization pulse laser transmission control optical path to be in a closed state, and the step of controlling the polarization pulse laser device to output the second polarization pulse laser specifically includes: controlling the S-polarization pulse laser transmission control optical path to be in a closed state and controlling the P-polarization pulse laser transmission control optical path to be in an open state.

[0093] When the first polarization pulse laser is a P polarization pulse laser and the second polarization pulse laser is an S polarization pulse laser, the step of controlling the polarization pulse laser device to output the first polarization pulse laser specifically includes: controlling the P polarization pulse laser transmission control optical path to be in an open state and controlling the S polarization pulse laser transmission control optical path to be in a closed state, and the step of controlling the polarization pulse laser device to output the second polarization pulse laser specifically includes: controlling the P polarization pulse laser transmission control optical path to be in a closed state and controlling the S polarization pulse laser transmission control optical path to be in an open state.

[0094] That is to say, by controlling the working state (on state or off state) of the P-polarized pulse laser transmission control optical path and the S-polarized pulse laser transmission control optical path, the output of the polarized pulse laser device can be controlled.

[0095] In some embodiments, the dimming window 112 is an electrically controlled birefringent optical crystal window, that is, the refractive index of the optical crystal is controlled by an external electric field, so that the light angle of the emitted light can be adjusted to achieve control of the spot position of the pulsed laser.

[0096] In some embodiments, an optical waveguide 100 and an optical waveguide support frame 111 for fixing the optical waveguide 100 are further disposed between the dimming window 112 and the intermediate light guiding reflection prism.

[0097] In some embodiments, a quartz support ring 103 for supporting the tray 104 and capable of rotation is disposed under the tray 104 ; a heater 102 and a heater support frame 101 are disposed inside the quartz support ring 103 and below the tray 104 , and the temperature of the substrate 105 can be effectively controlled by the heater 102 .

[0098] In some embodiments, a temperature sensor 109 is further disposed on the top of the reaction chamber 100 for sensing the temperature inside the reaction chamber 100 .

[0099] The following will combine a specific example to explain the preparation Figure 1 The process of forming the semiconductor quantum well structure is described in detail, wherein the first raised stripes on the quantum barrier layer are formed by S-polarized pulse laser modulation, and the second raised stripes on the quantum barrier layer are formed by P-polarized pulse laser modulation. Figure 6 A flow chart of a method for preparing a semiconductor quantum well structure provided by an embodiment of the present disclosure. Figure 6 As shown, the preparation method comprises the following steps:

[0100] BZ1. Place the gallium nitride substrate on the tray of the reaction chamber, start the tray rotation at a speed of 30 rpm; introduce hydrogen carrier gas into the reaction chamber, and adjust the pressure of the reaction chamber to 300 mbar; heat the gallium nitride substrate to 1060°C, and sequentially introduce ammonia, trimethylgallium vapor and silane gas into the reaction chamber to epitaxially grow a layer of n-type doped gallium nitride layer (i.e., n-type semiconductor layer) with a thickness of 3 μm on the gallium nitride substrate.

[0101] BZ2, turn off silane and trimethylgallium vapor in turn, and then adjust the temperature of the gallium nitride substrate to 720°C.

[0102] BZ3. The gas introduced into the reaction chamber is switched to trimethylgallium vapor, ammonia and hydrogen carrier gas, and a barrier base layer with a thickness of 4 nm is grown on the n-type doped gallium nitride layer.

[0103] BZ4. Continue to introduce trimethylgallium vapor, ammonia and hydrogen carrier gas into the reaction chamber, turn on the S-polarized pulse laser source filter, and place the irradiation spot of the S-polarized pulse laser on the center of the barrier base layer. Then adjust the incident angle of the S-polarized pulse laser through the dimming window, so that the irradiation spot of the S-polarized pulse laser moves from the surface center of the barrier base layer to the edge along the radial direction. Combined with the rotation of the tray, the irradiation spot of the S-polarized pulse laser forms a circular scan on the gallium nitride substrate, thereby growing a pulse laser modulated barrier layer with a thickness of 5nm.

[0104] Among them, in the process of generating the barrier modulation layer, the gas used to grow the barrier material is continuously introduced to prevent the barrier material from decomposing. This is because after growing a thicker barrier base layer, the growth gas is stopped and then scanned by laser. At this time, the barrier base layer will decompose. For this barrier decomposition process, the first thing to be decomposed is the periodic raised stripe structure. Therefore, a certain concentration of reaction gas needs to be maintained during the laser scanning process.

[0105] BZ5. Turn off the S-polarized pulse laser source filter.

[0106] BZ6. Switch the gas introduced into the reaction chamber to trimethylgallium vapor, trimethylindium vapor, ammonia and hydrogen carrier gas, and grow a well layer base layer with a thickness of 2 nm on the quantum barrier layer.

[0107] BZ7. Continue to introduce trimethylgallium vapor, trimethylindium vapor, ammonia and hydrogen carrier gas into the reaction chamber, turn on the P-polarized pulse laser source filter, and place the irradiation spot of the P-polarized pulse laser on the center of the well layer base layer. Then adjust the incident angle of the P-polarized pulse laser through the dimming window so that the irradiation spot of the P-polarized pulse laser moves from the surface center of the well layer base layer to the edge along the radial direction. Combined with the rotation of the tray, the irradiation spot of the P-polarized pulse laser forms a circular scan on the gallium nitride substrate, thereby growing a pulse laser modulated well layer with a thickness of 3nm.

[0108] Similarly, in the process of generating the well layer modulation layer, the gas used to grow the well layer material is continuously introduced in order to prevent the well layer material from decomposing.

[0109] BZ8. Turn off the P-polarized pulse laser source filter.

[0110] BZ3 to BZ8 are repeatedly executed for n times (n≥2, for example, n=6) to obtain an n-layer quantum well structure.

[0111] BZ9, grow a barrier layer with a thickness of 8nm; then grow a P-type doped gallium nitride layer (ie, p-type semiconductor layer) with a thickness of 60nm.

[0112] Based on the same inventive concept, the disclosed embodiment also provides a semiconductor quantum well structure, which is prepared by any preparation method provided in the previous embodiment. For the relevant description of the semiconductor quantum well structure, please refer to the previous corresponding content, which will not be repeated here.

[0113] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A method for preparing a semiconductor quantum well structure, characterized in that: include: forming an n-type semiconductor layer on one side of the substrate; A multi-quantum well structure is formed on a side of the n-type semiconductor layer facing away from the substrate, the multi-quantum well structure includes quantum barrier layers and quantum well layers that are alternately arranged, the material of the quantum well layer includes: indium gallium nitride, the quantum barrier layer includes: a barrier layer base layer and a barrier layer modulation layer located on the side of the barrier layer base layer facing away from the substrate, the barrier layer modulation layer includes a plurality of first raised stripes that are periodically arranged along a preset first direction, the quantum well layer includes: a well layer base layer and a well layer modulation layer located on the side of the well layer base layer facing away from the substrate, the well layer modulation layer includes a plurality of second raised stripes that are periodically arranged along a preset second direction, one of the preset first direction and the preset second direction is a circumferential direction of the substrate, and the other is a radial direction of the substrate; A p-type semiconductor layer is formed on the side of the multi-quantum well structure facing away from the substrate.

2. The preparation method according to claim 1, characterized in that: The step of forming a multi-quantum well structure on the side of the n-type semiconductor layer facing away from the substrate comprises: alternately performing the step of forming a quantum barrier layer and the step of forming a quantum well layer; The steps of forming the quantum barrier layer include: The step of generating a barrier layer base layer: generating a barrier layer material film on a first intermediate product structure to obtain a barrier layer base layer, wherein the first intermediate product structure at least includes the substrate and the n-type semiconductor layer; The step of generating a barrier layer modulation layer: continuously growing a barrier layer material on the barrier layer base layer, and simultaneously controlling the substrate to rotate at a first rotation speed and controlling a light spot of a first polarized pulsed laser to move from the center of the surface of the barrier layer base layer along a preset straight line pointing direction toward the edge of the surface of the barrier layer base layer at a first linear motion speed, so as to induce the formation of a first raised stripe, thereby obtaining a barrier layer modulation layer; The steps of forming a quantum well layer include: The step of generating a well layer base layer: growing a well layer material film on a second intermediate product structure to obtain a well layer base layer, wherein the second intermediate product structure at least includes the substrate, the n-type semiconductor layer and at least one quantum barrier layer; The step of generating a well layer modulation layer: continuously growing a well layer material on the barrier layer base layer, and simultaneously controlling the substrate to rotate at a second rotation speed and controlling the light spot of a second polarized pulsed laser to move from the center of the surface of the well layer base layer along the preset straight line pointing direction toward the edge of the surface of the well layer base layer at a second linear motion speed, so as to induce the formation of a second raised stripe, thereby obtaining a well layer modulation layer; Among them, one of the first polarized pulse laser and the second polarized pulse laser is an S-polarized pulse laser, and the other is a P-polarized pulse laser.

3. The preparation method according to claim 2, characterized in that: The first rotation speed is N1 rpm, the diameter of the spot of the first polarized pulse laser is D1 mm, and the first linear motion speed is V1 mm / min, wherein N1, D1 and V1 satisfy: V1=D1 / N1; And / or, the second rotation speed is N2 rpm, the diameter of the spot of the second polarized pulse laser is D2 mm, and the second linear motion speed is V2 mm / min, wherein N2, D2 and V2 satisfy: V2=D2 / N2.

4. The preparation method according to claim 2, characterized in that: The energy of a single photon of the first polarized pulsed laser is 0.95 to 1.05 times the energy band gap of the barrier layer base layer material, and the energy density per unit area of ​​the first polarized pulsed laser is lower than the ablation threshold of the barrier layer base layer material; And / or, the energy of a single photon of the second polarized pulse laser is 0.95 to 1.05 times the energy band gap of the well layer base layer material, and the energy density per unit area of ​​the second polarized pulse laser is lower than the ablation threshold of the well layer base layer material.

5. The preparation method according to claim 2, characterized in that: The step of forming a multi-quantum well structure on the side of the n-type semiconductor layer facing away from the substrate is implemented based on a thin film deposition device, the thin film deposition device comprising: a polarization pulse laser device, a reaction chamber, a tray and a dimming window, the tray is located in the reaction chamber and can rotate, the polarization pulse laser device is arranged outside the reaction chamber, the dimming window is located at the top of the reaction chamber, the polarization pulse laser device is configured to emit a P-polarization pulse laser or an S-polarization pulse laser toward the dimming window, and the dimming window is configured to adjust the light emission direction of the incident P-polarization pulse laser or S-polarization pulse laser; The step of generating a barrier layer base layer specifically includes: controlling a tray carrying a first intermediate product structure to rotate, introducing a barrier layer growth gas into the reaction chamber, and controlling a polarized pulse laser device not to output a pulse laser, so as to generate a barrier layer material film on the first intermediate product to obtain a barrier layer base layer; The step of generating a barrier layer modulation layer comprises: controlling a tray carrying a first intermediate product structure to rotate at a first rotation speed, controlling a polarization pulse laser device to output a first polarization pulse laser, and controlling the light emitting direction of the first polarization pulse laser through a dimming window so that a light spot of the first polarization pulse laser moves from the center of the surface of the barrier layer base layer along a preset straight line pointing direction toward the edge of the surface of the barrier layer base layer at a first linear motion speed, so as to induce the formation of a first raised stripe, thereby obtaining a barrier layer modulation layer; The step of generating the well layer foundation layer specifically includes: controlling the tray carrying the second intermediate product structure to rotate, introducing a well layer growth gas into the reaction chamber, and controlling the polarization pulse laser device not to output pulse laser, so as to generate a well layer material film on the second intermediate product to obtain the well layer foundation layer; The steps of generating a well layer modulation layer include: controlling a tray carrying a second intermediate product structure to rotate at a second rotation speed, controlling a polarization pulse laser device to output a second polarization pulse laser, and controlling the light emitting direction of the first polarization pulse laser through a dimming window so that the light spot of the first polarization pulse laser moves from the center of the surface of the well layer base layer along a preset straight line pointing direction toward the edge of the surface of the well layer base layer at a second linear motion speed to induce formation of a second raised stripe to obtain a well layer modulation layer.

6. The preparation method according to claim 5, characterized in that: The polarization pulse laser device comprises: a pulse laser source configured to generate pulse laser light; A filter lens configured to convert the pulsed laser output by the pulsed laser source into linearly polarized light; A beam splitter prism configured to transmit a portion of the linearly polarized light emitted from the filter lens to obtain an S-polarized pulse laser, and reflect another portion to obtain a P-polarized pulse laser; The S-polarized pulse laser transmission control optical path has an on state and an off state, and is configured to enable the S-polarized pulse laser emitted from the beam splitter prism to be transmitted to the intermediate light-guiding reflective prism through the S-polarized pulse laser transmission control optical path when in the on state, and to prevent the S-polarized pulse laser emitted from the beam splitter prism from being transmitted to the intermediate light-guiding reflective prism when in the off state; A P-polarized pulse laser transmission control optical path, having an on state and an off state, and configured to enable the P-polarized pulse laser emitted from the beam splitter prism to be transmitted to the intermediate light-guiding reflective prism through the P-polarized pulse laser transmission control optical path when in the on state, and to prevent the P-polarized pulse laser emitted from the beam splitter prism from being transmitted to the intermediate light-guiding reflective prism when in the off state; The intermediate light-guiding reflecting prism is configured to direct the input S-polarized pulse laser or P-polarized pulse laser toward the dimming window by the principle of reflection.

7. The preparation method according to claim 6, characterized in that: The step of controlling the polarized pulse laser device not to output pulse laser specifically includes: controlling the S-polarized pulse laser transmission control optical path and the P-polarized pulse laser transmission control optical path to be in a closed state; When the first polarized pulse laser is an S polarized pulse laser and the second polarized pulse laser is a P polarized pulse laser, the step of controlling the polarized pulse laser device to output the first polarized pulse laser specifically includes: controlling the S polarized pulse laser transmission control optical path to be in an open state and controlling the P polarized pulse laser transmission control optical path to be in a closed state, and the step of controlling the polarized pulse laser device to output the second polarized pulse laser specifically includes: controlling the S polarized pulse laser transmission control optical path to be in a closed state and controlling the P polarized pulse laser transmission control optical path to be in an open state; When the first polarization pulse laser is a P polarization pulse laser and the second polarization pulse laser is an S polarization pulse laser, the step of controlling the polarization pulse laser device to output the first polarization pulse laser specifically includes: controlling the P polarization pulse laser transmission control optical path to be in an open state and controlling the S polarization pulse laser transmission control optical path to be in a closed state, and the step of controlling the polarization pulse laser device to output the second polarization pulse laser specifically includes: controlling the P polarization pulse laser transmission control optical path to be in a closed state and controlling the S polarization pulse laser transmission control optical path to be in an open state.

8. The preparation method according to claim 5, characterized in that: The dimming window is an electrically controlled birefringent optical crystal window.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The thickness of the barrier layer base layer is 1 to 10 nm, and the thickness of the barrier layer modulation layer is 2 to 10 nm; The thickness of the well layer foundation layer is 1-10 nm, and the thickness of the well layer modulation layer is 2-10 nm.

10. A semiconductor quantum well structure, characterized in that: The method is prepared by any one of claims 1 to 9.

Images