Quantum dot based on quaternary antimonide cover layer and growth method thereof

Abstract

The invention discloses a quantum dot based on a quaternary antimonide cover layer and a growth method thereof, and the growth method comprises the steps: removing an oxide layer from a substrate, and carrying out the degassing; growing a first GaAs buffer layer on the substrate; growing an AlGaAs buffer layer on the first GaAs buffer layer; growing a second GaAs buffer layer on the AlGaAs buffer layer; growing an InGaAs quantum well on the second GaAs buffer layer; growing an InAs quantum dot on the InGaAs quantum well; and growing an InGaAsSb stress buffer layer on the InAs quantum dots at a fourth set temperature, maintaining the fourth set temperature, growing a GaAs cover layer on the InGaAsSb stress buffer layer, heating the substrate to a first set temperature, and growing a GaAs spacer layer on the GaAs cover layer. The light-emitting wavelength of the quantum dot can be further shifted to the E wave band from the C wave band through the quaternary antimonide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum dot growth, in particular to a quantum dot based on a quaternary antimonide cap layer and a growth method thereof. BACKGROUND

[0002] 1.38 μm band InAs / GaAs quantum dots, with their unique optical properties in the near-infrared region and flexible band gap control ability, have become a frontier research direction in the field of optoelectronics in recent years. This wavelength is in the "biological window" of low absorption of human tissue, which can achieve large imaging depth and high spatial resolution, and is particularly suitable for biomedical imaging technologies such as optical coherence tomography (OCT), providing a stable and reliable broadband light source. At the same time, the 1.38 μm wavelength is at the long-wave end of the traditional communication O band, and has low transmission dispersion in optical fibers, so it has great potential in data centers, high-speed on-chip optical interconnection, and short-distance data transmission systems. In addition, this band avoids the absorption peaks of the eye lens and retina tissue, has a higher safety threshold, making it more competitive in automotive laser radar, industrial ranging, and optoelectronic sensor applications in consumer electronics products.

[0003] Relying on the mature GaAs semiconductor platform and self-assembly growth technology, 1.38 μm InAs / GaAs quantum dots can be combined with existing AlGaAs / GaAs distributed Bragg reflector (DBR) and MEMS-HCG micro-mechanical grating structures to build a variety of high-performance devices.

[0004] For example, high-power vertical-cavity surface-emitting laser (VCSEL) arrays, narrow linewidth and broadband tunable lasers, and broadband superluminescent diodes (SLEDs) can be developed to meet a wide range of application requirements. InAs / GaAs quantum dots themselves also have high quantum efficiency and low threshold current, and exhibit good temperature stability and low power consumption characteristics, making them particularly attractive in high-speed modulation and low-power optoelectronic integrated systems.

[0005] However, fully leveraging the advantages of 1.38 μm InAs / GaAs quantum dots in practical research and large-scale applications still faces numerous technical challenges. The primary difficulty lies in extending the quantum dot emission wavelength beyond the traditional 1.3–1.35 μm range to longer wavelengths. This stems from the significant lattice constant mismatch between the GaAs substrate and the InAs material: as the quantum dot size increases to obtain longer wavelengths, strain accumulation increases significantly, easily inducing lattice defects such as dislocations and point defects. These defects not only reduce the optical quality of the quantum dot material but may also severely impair the radiative recombination efficiency of the device, affecting its stability and lifetime. Furthermore, with the redshift of wavelength, the thermal stability of quantum dot materials becomes more prominent. Under high-temperature operating conditions, In is prone to diffusion and redistribution, leading to changes in quantum dot size and even structural degradation, thereby affecting the stability and reliability of its optical performance. Summary of the Invention

[0006] This invention provides a quantum dot based on a quaternary antimony capping layer and its growth method to solve the technical problems mentioned in the background art.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows: This invention provides a method for growing quantum dots based on a quaternary antimony capping layer, comprising the following steps: S1. Remove the oxide layer from the substrate under a set environment and perform a degassing operation on the substrate; S2. A first GaAs buffer layer is grown on the substrate surface using molecular beam epitaxy at a first set temperature; S3. Grow an AlGaAs buffer layer on the first GaAs buffer layer at the second set temperature. S4. A second GaAs buffer layer is grown on the AlGaAs buffer layer at the first set temperature. S5. InGaAs quantum well is grown on the second GaAs buffer layer at the third set temperature, wherein the velocity-to-flow ratio of group V elements and group III elements in the growth cavity is within a set range during the growth of InGaAs quantum well. S6. InAs quantum dots are grown on InGaAs quantum wells using self-assembly technology; S7. Grow an InGaAsSb stress buffer layer on the InAs quantum dot at a fourth set temperature, then maintain the fourth set temperature and grow a GaAs capping layer on the InGaAsSb stress buffer layer. Then heat the substrate to the first set temperature and grow a GaAs spacer layer on the GaAs capping layer.

[0008] Further, the substrate is selected from one of GaAs substrate, and various GaAs pseudo-substrates. The GaAs pseudo-substrate is a heterostructure built on a GaAs substrate by epitaxial growth technology. The various GaAs pseudo-substrates include GaAs / Si pseudo-substrate, GaAs / SiC pseudo-substrate, and GaAs / sapphire pseudo-substrate.

[0009] Further, the S1 specifically includes the following steps: S11, placing the substrate in a molecular beam epitaxy instrument MBE, and then raising the temperature of the substrate to 550-620°C in an environment where the speed ratio of group V elements and group III elements is higher than a set ratio, so as to remove the oxidation layer on the surface of the substrate; S12, then raising the temperature of the substrate to 600-650°C and keeping for a set time, so as to complete the degassing of the substrate.

[0010] Further, the S2 is implemented in the following manner: using the molecular beam epitaxy technology to grow a first GaAs buffer layer on the surface of the substrate at a temperature of 500-600°C, and the thickness of the first GaAs buffer layer is set according to requirements.

[0011] Further, the S3 specifically includes the following steps: S31, raising the temperature of the substrate to 620-650°C; S32, using the molecular beam epitaxy technology to grow an AlGaAs buffer layer on the first GaAs buffer layer at a temperature of 620-650°C, until the thickness of the AlGaAs buffer layer reaches 50-1400 nm, and the component of aluminum elements in the AlGaAs buffer layer is maintained at 30-45%.

[0012] Further, the S4 specifically includes the following steps: S41, reducing the temperature of the substrate to 500-600°C; S42, using the molecular beam epitaxy technology to grow a second GaAs buffer layer on the AlGaAs buffer layer at a temperature of 500-600°C, and the growth thickness of the second GaAs buffer layer is 30-70 nm.

[0013] Further, the S5 specifically includes the following steps: S51, controlling the temperature of the substrate to be 450-600°C; S52, growing InGaAs quantum well on the second GaAs buffer layer at a temperature of 450-600 DEG C, wherein the speed flow ratio of V group element and III group element in the growth chamber of the molecular beam epitaxy instrument MBE where the InGaAs quantum well is located is in the range of 15-45; the V group element refers to arsenic element, and the III group element refers to the sum of indium element and gallium element.

[0014] Further, the implementation mode of S6 is: InAs quantum dots are grown on the InGaAs quantum well by using the molecular beam epitaxy technology or the chemical vapor deposition method, and the thickness of the InAs material is 1-2 nm.

[0015] Further, S7 specifically includes the following steps: S71, controlling the temperature of the substrate to be 460-550 DEG C, and then growing 3-10 nm thick InGaAsSb stress buffer layer on the InAs quantum dots, wherein the component of In element in the InGaAsSb stress buffer layer is 15-22%, and the component of Sb element is not more than 16%; S72, maintaining the temperature of the substrate at 460-550 DEG C, and then growing 4-20 nm GaAs cap layer on the InGaAsSb stress buffer layer; S73, then increasing the temperature of the substrate to 500-600 DEG C, and growing GaAs spacer layer on the GaAs cap layer, and the thickness of the GaAs spacer layer is set according to the modulation speed.

[0016] Another aspect of the present application also provides a quantum dot based on a quaternary antimonide cap layer, which is prepared by using the above growth method.

[0017] The present application has the following beneficial effects: The present application provides a growth method of quantum dot based on quaternary antimonide cap layer. The method uses quaternary antimonide cap layer (i.e. InGaAsSb stress buffer layer), reduces the stress on InAs quantum dots, thereby increases the size of the quantum dots, realizes the red shift of the InAs quantum dot emission wavelength, and can red shift the InAs quantum dot emission wavelength from C band (wavelength range of 1530-1565 nm) to E band (wavelength range of 1360-1460 nm). BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a structure schematic diagram of the quantum dot based on quaternary antimonide cap layer in the present application. DETAILED DESCRIPTION

[0019] For the purpose of facilitating the understanding of the present application, a more comprehensive description of the present application will be given below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in many other different forms, and is not limited to the embodiments described herein. On the contrary, these embodiments are provided for the purpose of making the disclosure of the present application more thorough and comprehensive.

[0020] In addition, the terms "first", "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0021] With reference to Figure 1 The embodiments of the present application provide a growth method of quantum dots based on a quaternary antimonide cap layer, comprising the following steps: S1, removing the oxidation layer of the substrate in a set environment, and performing a degassing operation on the substrate; S2, using a molecular beam epitaxy technique to grow a first GaAs buffer layer on the surface of the substrate at a first set temperature; the main function of the first GaAs buffer layer is to repair the surface damage layer possibly generated by the deoxidization of the substrate, and the repair mainly includes flattening the surface of the substrate, healing dislocations, and isolating substrate impurities, etc.; S3, growing an AlGaAs buffer layer on the first GaAs buffer layer at a second set temperature; the main function of the AlGaAs buffer layer is to limit the propagation of light, and to confine the light in the active region on this layer. And its band gap is wider than that of GaAs, which can also confine the carriers in the active region; S4, growing a second GaAs buffer layer on the AlGaAs buffer layer at the first set temperature; the main function of the second GaAs buffer layer is to make the surface of the quantum dots be the GaAs surface under the same condition before each growth, which is beneficial to the subsequent accurate control of the In element composition. And it forms a confinement layer with the previous AlGaAs layer; S5, growing an InGaAs quantum well on the second GaAs buffer layer at a third set temperature, wherein the speed flow ratio of the group V element and the group III element in the growth cavity is within a set interval during the growth of the InGaAs quantum well; wherein the growth cavity contains the required gas source and related detectors; the main function of the InGaAs quantum well is to reduce the strain difference between the InAs quantum dot (QD) and GaAs, so as to make the quantum dot larger, the wavelength longer, the uniformity better, the quantum dot density higher, and to help the quantum dot to capture carriers; S6, growing InAs quantum dots on the InGaAs quantum well by using a self-assembly technique; S7, growing an InGaAsSb stress buffer layer on the InAs quantum dots at a fourth set temperature, then maintaining the fourth set temperature, and growing a GaAs cap layer on the InGaAsSb stress buffer layer, then raising the temperature of the substrate to a first set temperature, and growing a GaAs spacer layer on the GaAs cap layer.

[0022] The main role of the InGaAsSb stress buffer layer is to change the shape of the quantum dots by stress, so as to change the light-emitting wavelength thereof; The main role of the GaAs cap layer is to encapsulate the active region, prevent the decomposition of Sb element, and ensure the size (height) of the quantum dots. Finally, the GaAs cap layer provides a transition zone for the GaAs spacer layer generated at a high temperature later, and forms a carrier barrier; The main role of the GaAs spacer layer is to eliminate the interlayer strain coupling and tunneling coupling, and ensure that the growth initial conditions of each layer of quantum dots are the same.

[0023] The application uses a quaternary antimonide cap layer (i.e. the InGaAsSb stress buffer layer), reduces the stress on the InAs quantum dots, increases the size of the quantum dots, and realizes the red shift of the light-emitting wavelength of the InAs quantum dots.

[0024] In some embodiments, the substrate is selected from one of GaAs substrates and various GaAs pseudo-substrates. The GaAs pseudo-substrate is a heterostructure constructed on a GaAs substrate by epitaxial growth technology. The selection of the GaAs substrate can reduce defects and improve optical performance; The various GaAs pseudo-substrates include GaAs / Si pseudo-substrates, GaAs / SiC pseudo-substrates, and GaAs / sapphire pseudo-substrates; The GaAs / Si pseudo-substrate indicates that a GaAs layer is grown on a silicon substrate. The low cost and mature process of silicon can reduce the cost of optoelectronic devices; The GaAs / SiC pseudo-substrate indicates that a GaAs layer is grown on a silicon carbide substrate. The high thermal conductivity of SiC and the high frequency characteristics of GaAs can improve the power of electronic devices (such as microwave devices); The GaAs / sapphire pseudo-substrate indicates that a GaAs layer is grown on a sapphire substrate. The sapphire has high transparency and stability, and is mainly suitable for optoelectronic devices (such as lasers and detectors).

[0025] In the embodiment, the substrate is preferably a GaAs substrate.

[0026] In some embodiments, the S1 specifically comprises the following steps: S11, place the substrate in a molecular beam epitaxy instrument MBE, and then heat the substrate to 550-620 DEG C in an environment with a V element and III element flow ratio higher than a set ratio to remove the oxide layer on the surface of the substrate; specifically, the selected environment is an arsenic-rich environment or an environment with a V / III ratio of 30 times higher than the normal growth of gallium arsenide, wherein the V / III ratio is the flow ratio of the five-element arsenic and the III element; but the environment in the embodiment of the application is preferably an arsenic-rich environment; the selection of the arsenic-rich environment can protect the surface of the substrate, reduce the decomposition of the surface GaAs, reduce the formation of roughness and pits, and also promote the decomposition of the oxide; S12, then heat the substrate to 600-650 DEG C and keep for a set time (such as about 10 minutes) to complete the degassing of the substrate; the gas here includes air attached to the substrate, and also includes impurity gas (such as most of the water vapor, organic solvent residue, CO, CO2, etc.) brought in during the manufacture of the substrate.

[0027] In some embodiments, the implementation of S2 is as follows: Use the molecular beam epitaxy technology on the surface of the substrate and grow the first GaAs buffer layer at a temperature of 500-600 DEG C, and the thickness of the first GaAs buffer layer is set according to the requirements; the general principle of the thickness of the first GaAs buffer layer is that the thickness of the first GaAs buffer layer is not less than 150 nm, so that a relatively flat first GaAs buffer layer is obtained, which is convenient for subsequent growth.

[0028] In some embodiments, S3 specifically includes the following steps: S31, increase the temperature of the substrate to 620-650 DEG C; S32, use the molecular beam epitaxy technology to grow the AlGaAs buffer layer on the first GaAs buffer layer at a temperature of 620-650 DEG C until the thickness of the AlGaAs buffer layer reaches 50-1400 nm, wherein the component of the aluminum element in the AlGaAs buffer layer is maintained at 30-45% to limit the propagation of light.

[0029] In some embodiments, S4 specifically includes the following steps: S41, reduce the temperature of the substrate to 500-600 DEG C; S42, use the molecular beam epitaxy technology to grow the second GaAs buffer layer on the AlGaAs buffer layer at a temperature of 500-600 DEG C, and the growth thickness of the second GaAs buffer layer is 30-70 nm.

[0030] In some embodiments, S5 specifically includes the following steps: S51, control the temperature of the substrate to be 450-600 DEG C; S52, growing InGaAs quantum well on the second GaAs buffer layer at a temperature of 450℃-600℃, wherein the speed ratio of V group element and III group element in the growth cavity of the molecular beam epitaxy instrument MBE where the InGaAs quantum well is located is in the interval of 15-45, so that the InGaAs quantum well is long and covers the entire wafer (i.e. substrate) surface, so as to reach the suitable high-performance quantum dot growth condition; the V group element refers to arsenic element, and the III group element refers to the sum of indium element and gallium element.

[0031] In some embodiments, the implementation manner of S6 is: InAs material with a thickness of 1nm-2nm is grown on the InGaAs quantum well by using a molecular beam epitaxy technology or a chemical vapor deposition method, and then InAs quantum dots are grown on the InAs material by using a self-assembly technology.

[0032] In some embodiments, S7 specifically comprises the following steps: S71, controlling the temperature of the substrate at 460℃-550℃, and then growing an InGaAsSb stress buffer layer (i.e. quaternary antimony cap layer) on the InAs quantum dot, wherein the composition, temperature and thickness of the InGaAsSb stress buffer layer need to be accurately controlled, otherwise the performance of the quantum dot cannot reach the expectation. The thickness of the InGaAsSb stress buffer layer is generally about 3nm-10nm; wherein the composition of In element in the InGaAsSb stress buffer layer is 15%-22%, and the composition of Sb element is not more than 16%; compared with common InGaAs, the Sb element in the InGaAsSb stress buffer layer has a surfactant effect, which can effectively prevent In-Ga interdiffusion and maintain the quantum dot size. Meanwhile, the composition of Sb element cannot be too large (i.e. more than 16%), otherwise the InGaAsSb will become Type II, which is not suitable for the 1.38um cap layer. In addition, the lattice constant of InGaAsSb is larger, which can make the light-emitting wavelength of the quantum dot longer. S72, maintaining the temperature of the substrate at 460℃-550℃, and then growing a GaAs cap layer with a thickness of 4nm-20nm on the InGaAsSb stress buffer layer; S73, then increasing the temperature of the substrate to 500℃-600℃, and growing a GaAs spacer layer on the GaAs cap layer, wherein the thickness of the GaAs spacer layer is set according to the modulation speed.

[0033] The red shift principle of the light-emitting wavelength of the InAs quantum dot in the application is as follows: Since the commonly used InGaAs cap layer is difficult to effectively promote the further red shift of the quantum dot light-emitting wavelength. Therefore, the present application appropriately introduces Sb element in the InGaAs cap layer to form an InGaAsSb quaternary antimonide cap layer, which has a further increased lattice constant compared with the InGaAs cap layer, and can effectively reduce the compressive stress applied on the InAs quantum dot during the covering process. This strain buffer effect helps the InAs quantum dot to maintain a larger size (especially in the vertical direction) during the subsequent covering growth, thereby reducing the quantum confinement energy level, reducing the inter-level transition energy, and realizing the wavelength red shift. In addition, the Sb element has significant surface activity in epitaxial growth, and its addition can effectively reduce the surface energy and atomic migration barrier of the growth surface, significantly enhancing the surface migration ability of In atoms during the covering growth stage. The enhanced In atom migration property is conducive to the more uniform enrichment of In atoms to the central region of the InAs quantum dot, and inhibits its diffusion to the surrounding covering layer. Therefore, the size of the InAs quantum dot can not only be increased and increased, but also the uniformity of its size distribution is significantly improved, which further promotes the effective red shift of the light-emitting wavelength of the InAs quantum dot.

[0034] With reference to Figure 1 In another aspect, the present application also provides a quantum dot based on a quaternary antimonide cap layer, which is prepared by using the above growth method.

[0035] The above describes only the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Moreover, the technical solutions of each embodiment of the present application can be combined with each other, but it must be based on the realization of the ordinary skilled person in the art. When the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for growing quantum dots based on a quaternary antimony oxide capping layer, characterized in that, Includes the following steps: S1. Remove the oxide layer from the substrate under a set environment and perform a degassing operation on the substrate; S2. A first GaAs buffer layer is grown on the substrate surface using molecular beam epitaxy at a first set temperature; S3. Grow an AlGaAs buffer layer on the first GaAs buffer layer at the second set temperature. S4. A second GaAs buffer layer is grown on the AlGaAs buffer layer at the first set temperature. S5. InGaAs quantum well is grown on the second GaAs buffer layer at the third set temperature, wherein the velocity-to-flow ratio of group V elements and group III elements in the growth cavity is within a set range during the growth of InGaAs quantum well. S6. InAs quantum dots are grown on InGaAs quantum wells using self-assembly technology; S7. Grow an InGaAsSb stress buffer layer on the InAs quantum dot at a fourth set temperature, then maintain the fourth set temperature and grow a GaAs capping layer on the InGaAsSb stress buffer layer. Then heat the substrate to the first set temperature and grow a GaAs spacer layer on the GaAs capping layer.

2. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, The substrate is selected from GaAs substrates and a variety of GaAs pseudo-substrates; a GaAs pseudo-substrate is a heterostructure constructed on a GaAs substrate by epitaxial growth technology; Various GaAs pseudo-substrates include GaAs / Si pseudo-substrates, GaAs / SiC pseudo-substrates, and GaAs / sapphire pseudo-substrates.

3. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, S1 specifically includes the following steps: S11. Place the substrate in a molecular beam epitaxy (MBE) instrument, and then heat the substrate to 550°C~620°C in an environment where the flow rate ratio of group V elements and group III elements is higher than a set ratio, in order to remove the oxide layer on the substrate surface; group V elements refer to arsenic, and group III elements refer to the sum of indium and gallium. S12. Then, the substrate is heated to 600℃~650℃ and held for a set time to complete the degassing operation of the substrate.

4. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, The implementation of S2 is as follows: A first GaAs buffer layer is grown on the substrate surface using molecular beam epitaxy at a temperature of 500°C to 600°C. The thickness of the first GaAs buffer layer is set according to requirements.

5. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, S3 specifically includes the following steps: S31. Increase the substrate temperature to 620℃~650℃; S32. At a temperature of 620℃~650℃, an AlGaAs buffer layer is grown on the first GaAs buffer layer using molecular beam epitaxy until the thickness of the AlGaAs buffer layer reaches 50nm~1400nm, wherein the aluminum content in the AlGaAs buffer layer is maintained at 30%~45%.

6. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, S4 specifically includes the following steps: S41. Reduce the temperature of the substrate to 500℃~600℃; S42. At a temperature of 500℃~600℃, a second GaAs buffer layer is grown on the AlGaAs buffer layer using molecular beam epitaxy. The thickness of the second GaAs buffer layer is 30nm~70nm.

7. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, S5 specifically includes the following steps: S51. Control the temperature of the substrate at 450℃~600℃; S52. InGaAs quantum wells are grown on the second GaAs buffer layer at a temperature of 450℃~600℃, wherein the velocity-to-flow ratio of group V elements and group III elements in the growth chamber of the molecular beam epitaxy (MBE) instrument where the InGaAs quantum well is located is in the range of 15~45; group V elements refer to arsenic, and group III elements refer to the sum of indium and gallium.

8. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, The implementation method of S6 is as follows: InAs material with a thickness of 1 nm to 2 nm is grown on InGaAs quantum wells using molecular beam epitaxy or chemical vapor deposition, and then InAs quantum dots are grown on the InAs material using self-assembly technology.

9. The method for growing quantum dots based on a quaternary antimony capping layer according to claim 1, characterized in that, S7 specifically includes the following steps: S71. The temperature of the substrate is controlled at 460℃~550℃, and then an InGaAsSb stress buffer layer with a thickness of 3 nm~10 nm is grown on the InAs quantum dots, wherein the In element composition of the InGaAsSb stress buffer layer is 15%~22% and the Sb element composition does not exceed 16%; S72. Maintain the substrate temperature at 460℃~550℃, and then grow a 4nm~20nm GaAs capping layer on the InGaAsSb stress buffer layer. S73. Next, the substrate temperature is raised to 500℃~600℃, and a GaAs spacer layer is grown on the GaAs capping layer. The thickness of the GaAs spacer layer is set according to the modulation speed.

10. A quantum dot based on a quaternary antimony capping layer, characterized in that, Prepared using the growth method according to any one of claims 1 to 9.

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