Optical grade vanadium compensated 4H single crystal and 6H single crystal, as well as silicon carbide crystal and method for producing the same

Abstract

An optical device comprising a vanadium compensated high resistivity 6H or 4H polytype SiC single crystal, the SiC single crystal being used to transmit light with a wavelength in the range of 420 nm to 4.5 μm. The device may include a window, a lens, a prism, or a waveguide. A system comprising a source for generating light with a wavelength in the range of 420 nm to 4.5 μm and a device for receiving and transmitting the light, wherein the device comprises a vanadium compensated high resistivity 6H or 4H polytype SiC single crystal. The present disclosure also relates to crystals and methods for optical applications, the crystal comprising an aluminum-doped silicon carbide crystal, the aluminum-doped silicon carbide crystal having residual nitrogen and boron impurities, wherein the aluminum concentration is greater than the combined concentration of nitrogen and boron, and wherein the light absorption coefficient at a wavelength of about 400 nm to about 800 nm is less than about 0.4 cm ‑1 .

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 984,177, filed on March 2, 2020, and claims the benefit of U.S. Patent Application No. 17 / 029,746, filed on September 23, 2020. This application is a continuation of U.S. Patent Application No. 17 / 029,746. The entire disclosures of U.S. Provisional Patent Application No. 62 / 984,177 and U.S. Patent Application No. 17 / 029,746 are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to optical devices, optical transmission systems, compositions, and methods for preparing aluminum-doped silicon carbide crystals. Background Art

[0004] The present disclosure generally relates to optical devices for transmitting light energy or information, including but not necessarily limited to windows, lenses, prisms, and waveguides. The present disclosure also generally relates to systems and methods for transmitting light energy or information using optical devices.

[0005] The present disclosure also relates generally to silicon carbide crystals and methods for producing the same.More particularly, but not exclusively, the present disclosure relates to silicon carbide crystals that may be suitable for use in optical applications and to methods for producing the same. Summary of the invention

[0006] The present disclosure relates to vanadium compensated 4H hexagonal polytype and 6H hexagonal polytype silicon carbide (SiC) single crystals having low light absorption in their substantial transparency range, particularly but not necessarily limited to wavelengths in the range of about 420 nm to about 4.5 μm. The SiC single crystals according to the present disclosure can be used in a variety of optical applications, such as but not limited to optical windows, lenses, prisms, and waveguides operating in the visible and near infrared (IR) spectral ranges.

[0007] The present disclosure also relates to an optical device, comprising: a vanadium-compensated high-resistivity 6H polytype or 4H polytype SiC single crystal; wherein the SiC single crystal is configured to transmit light with a wavelength in the range of 420nm to 4.5μm. According to one aspect of the present disclosure, the optical device may include a window, lens, prism, or waveguide for transmitting light with a wavelength in the range of 420nm to 4.5μm.

[0008] The present disclosure also relates to an optical transmission system comprising: a light source for generating light with a wavelength in the range of 420 nm to 4.5 μm; and an optical device for receiving and transmitting the light, wherein the optical device comprises a vanadium-compensated high-resistivity 6H polytype or 4H polytype SiC single crystal.

[0009] In addition, in one embodiment, the composition includes an aluminum-doped silicon carbide crystal having residual nitrogen and boron impurities. The silicon carbide crystal includes aluminum in the silicon carbide crystal at a concentration greater than the combined concentration of nitrogen and boron in the silicon carbide crystal, and the silicon carbide crystal has a light absorption coefficient of less than about 0.4 cm at a wavelength in the range of about 400 nm to about 800 nm. -1 .

[0010] In another embodiment, a method for preparing an aluminum-doped silicon carbide crystal includes providing a silicon carbide source material and a silicon carbide single crystal seed in a growth crucible. The method also includes providing a solid aluminum dopant source material containing a compound containing aluminum and oxygen in a container. The growth crucible is heated in the following manner when the container is positioned in the growth crucible: the manner is effective to generate a silicon- and carbon-containing vapor from the silicon carbide source material in the growth crucible and to generate an aluminum-containing vapor from the solid aluminum dopant source material in the container, and to deposit the silicon- and carbon-containing vapor and the aluminum-containing vapor on the silicon carbide single crystal seed to grow an aluminum-doped silicon carbide crystal. The container contains a first material that resists damage to the aluminum dopant source and the aluminum-containing vapor, and a second material that resists damage to the silicon- and carbon-containing vapor. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a top view of one example of a silicon carbide (SiC) wafer constructed in accordance with the present disclosure;

[0012] Figure 2 yes Figure 1 Side view of SiC wafer;

[0013] Figure 3 is a schematic diagram of an example of an optical transmission system constructed according to the present disclosure;

[0014] Figure 4 is the transmission (T mes ) curve and reflection (R mes ) curve (T mes , R mes as a function of wavelength);

[0015] Figure 5 The transmission and reflection curves of some vanadium compensated 6H-SiC wafers (T mes , R mesas a function of wavelength);

[0016] Figure 6 is a graph showing light absorption curves (absorption coefficient as a function of wavelength) of two wafers;

[0017] Figure 7 is a graph showing transmission curves (transmittance as a function of wavelength) for six vanadium compensated 6H-SiC wafers;

[0018] Figure 8 is a graph of light absorption (absorption coefficient as a function of wavelength) of 4H-SiC wafer in the visible light range;

[0019] Fig. 9 is a graph of light absorption (absorption coefficient as a function of wavelength) of a 6H-SiC wafer in the visible light range;

[0020] Fig.10 is a schematic diagram of a system for sublimation growth of aluminum-doped silicon carbide crystals;

[0021] Fig.11 is used for Fig.10 A schematic diagram of a doping container in a system;

[0022] Fig.12 is the light absorption (α, cm) measured on 4H-SiC wafer -1 ) is a schematic diagram of the wavelength dispersion of ; and

[0023] Fig.13 is the light absorption (α, cm) measured on 6H-SiC wafer -1 ) is a schematic diagram of the wavelength dispersion of .

[0024] The same reference numbers or other feature indicators are used in the drawings to indicate the same or similar features. DETAILED DESCRIPTION

[0025] Figure 1 and 2 An example of a silicon carbide (SiC) wafer 10 constructed in accordance with the present disclosure is shown. Wafer 10 may have a face 12 and a cylindrical edge 14. As described in more detail below, wafer 10 may be a vanadium compensated, high resistivity 4H hexagonal or 6H hexagonal SiC single crystal. Figure 3 is a diagram of one example of an optical transmission system constructed according to the present disclosure. The transmission system may include a light source 18 for generating light 20, an optical device 16 for receiving and transmitting light 20, and a target 22 to which the light 20 is transmitted by the optical device 16.

[0026] Light 20 may have one or more wavelengths in the range of 420 nm to 4.5 μm. Optical device 16 may be fabricated from wafer 10 and may be, for example, a window for transmitting light 20 while providing a physical barrier between light source 18 and target 22, a lens for focusing or dispersing light 20, a prism for separating spectral components of light 20, or a waveguide for directing light 20 toward target 22.

[0027] SiC single crystals are used in certain semiconductor devices, including high-power and high-frequency diodes and transistors, ultrafast semiconductor optical switches, and detectors operating in harsh environments. Hexagonal SiC crystals can be used as substrates for epitaxial growth of SiC or gallium nitride (GaN) epitaxial layers. Nitrogen-doped n-type 4H-SiC crystals are used as substrates for epitaxial 4H-SiC power conversion diodes and transistors (e.g., MOSFETs). See U.S. Patent No. 8,507,986. High resistivity (semi-insulating) 4H-SiC crystals and 6H-SiC crystals are used as substrates for epitaxial GaN-based high-frequency transistors (e.g., HEMTs). See U.S. Patent No. 9,484,284.

[0028] Large-sized SiC single crystals can be grown from the gas phase by sublimation. See U.S. Patent No. 5,746,827. In preparation for growth, a SiC source, which may be in the form of SiC powder or grains, may be provided in a high temperature region of a graphite crucible. A SiC seed crystal, such as a single crystal SiC plate or wafer, is positioned in a lower temperature region of the crucible, for example, attached to a crucible lid. The crucible is heated to sublime the SiC source and fill the crucible with the gaseous products of the sublimation. The resulting vapor migrates to the cooler SiC seed crystal and deposits on the seed crystal to grow a SiC boule of appropriate size.

[0029] In order to meet certain requirements, dopants can be introduced into the growth system to change the electronic parameters of the grown SiC crystal, such as conductivity type and resistivity. Nitrogen doping can be used to manufacture low-resistivity n-type 4H-SiC single crystals. There are at least two types of compensated high-resistivity SiC single crystals, i.e., vanadium-compensated semi-insulating (VCSI) SiC crystals (see U.S. Patent No. 5,611,955) and high-purity semi-insulating (HPSI) SiC crystals (see U.S. Patent No. 7,601,441) manufactured using vanadium doping. The latter can be manufactured without doping and compensated by introducing deep energy level point defects.

[0030] The optical and spectral properties of various crystalline SiC forms have been studied in the ultraviolet (UV), visible and IR ranges. See Singh et al., Nonlinear Optical Properties of Hexagonal Silicon Carbide, Appl. Phys. Lett, Vol. 19, 2 (1971) 53-56. The region of substantial light transmission of 4H-SiC and 6H-SiC extends from a band edge cutoff in the visible to λ≈4.5 μm in the infrared, where transparency is terminated by a multiphonon absorption band (see, e.g., Singh et al., Nonlinear Optical Properties of Hexagonal Silicon Carbide, Appl. Phys. Lett, Vol. 19, 2 (1971) 53-56). Figure 1 ).

[0031] The mechanical, chemical and thermal properties of SiC can be attractive for various optical applications. Desired properties can include low density, high strength and hardness, high wear resistance, high thermal shock resistance, high thermal conductivity, and chemical stability. Polycrystalline 3C-SiC grown by chemical vapor deposition (CVD) has been studied as a potential material for mid-IR windows and domes working in harsh environments. See Goela et al., Transparent SiC for mid-IR windows and domes, SPIE Vol. 2286 (1994) 46-59.

[0032] Hexagonal single crystal SiC has been explored as a material for optical waveguides. See Luan et al., Optical ridgewaveguides in 4H-SiC single crystal produced by combination of carbon ionirradiation and femtosecond laser ablation, Optical Materials Express, Vol. 4, No. 6 (2014) 1166-1171; Japanese Patent No. 6002106 (Silicon Carbide Optical Waveguide Element); and Chinese Patent No. 103472533 (A method for preparing erbium-doped silicon carbide optical waveguides by ion implantation).

[0033] The light absorption of sublimation-grown 4H-SiC single crystals and 6H-SiC single crystals in the visible (VIS) to infrared range has been studied. See Wellmann et al., Optical Quantitative Determination of Doping Levels and Their Distribution in SiC, Mat. Sci. Eng. B 91-92 (2002) 75-78. These crystals have a high absorption rate of up to 1·10 18 cm -3 The amount of N, B and Al doped, and has poor light transmission. 4H-SiC crystals and 6H-SiC crystals have been studied for light transmission and reflection in the infrared. Cuia et al., Infrared Transmission and Reflectivity Measurements of 4H-and 6H-SiC Single Crystals, Mat. Sci. For. Vol. 821 to 823, pp. 265 to 268 (2015). The samples studied included pure (not intentionally doped), N-doped, B-doped, VCSI and HPSI. In all these studies, N-doped SiC crystals and B-doped SiC crystals showed significant optical losses with increasing dopant concentration. Pure SiC crystals show less loss, especially in the visible range. The best IR optical transparency was measured on semi-insulating VCSI samples and HPSI samples.

[0034] 4H-SiC and 6H-SiC belong to the 6mm space group and are positive uniaxial crystals. The dependence of the refractive index of semi-insulating 4H-SiC single crystals and 6H-SiC single crystals grown by sublimation on wavelength, polarization (ordinary vs. extraordinary) and temperature has been studied. See Xu et al., Temperature Dependence of Refractive Indices for 4H and 6H, J.Appl.Phys.115, 113501 (2014) 1-4. For these measurements, prisms with low apex angles were made from single crystals, with the prism edges parallel to the c-axis. It was found that the refractive index values ​​of 4H-SiC and 6H-SiC and their dispersion are actually the same.

[0035] Although large-size semi-insulating SiC single crystals (both VCSI and HPSI) are commercially available, there are no known industrial applications of such crystals in the field of transmission optics. This is probably due to residual optical losses in hexagonal SiC, which are not well understood or controlled. Various mechanisms that can cause light absorption in the fundamental transparency range of SiC have been discussed in the literature. These mechanisms include doping-induced bandgap narrowing, transitions involving dopants, impurities or defects (see, e.g., Atabaev et al., Spectral Dependence of Optical Absorption of 4H-SiC Doped with Boron and Aluminum, J. of Spectroscopy (2018) Article ID 8705658). Figure 1 ), intraband transitions and free carrier absorption.

[0036] Figures 1 to 3 The wafer 10 and the optical device 16 shown as examples in FIG. 1 may include a vanadium-compensated 6H polytype or 4H polytype SiC single crystal having excellent light transmission in the wavelength range of about 420 nm in the visible to about 4.5 μm in the near infrared. The SiC single crystal may be used as an optical material for applications in the field of transmission optics, such as, but not limited to, optical windows, lenses, prisms, and waveguides.

[0037] The SiC crystals described herein may be 4H-SiC crystals and 6H-SiC crystals compensated by vanadium grown by sublimation. During growth, the crystals may be doped (compensated) with vanadium to 9·10 16 cm -3 To 1.5·10 17 cm -3 The concentration of shallow impurities (such as N, B, and Al) can be controlled to not exceed 3·10 16 cm -3 Techniques for vanadium doping and shallow impurity control are described in U.S. Patents Nos. 7,608,524, 8,216,369, 8,361,227, 8,858,709, 9,017,629, and 9,090,989.

[0038] The SiC crystal constituting the wafer 10 or the optical device 16 may have a high structural quality without sized crystal defects (such as inclusions or subgrains) and a particle size of less than 1·10 4 cm -2The total dislocation density of the crystal is 2.34 × 10-1.87 mm / s. The overall crystal quality can be assessed using X-ray rocking curve techniques. X-ray reflections with a FWHM below 25 arc seconds can be a typical indication of high crystal quality.

[0039] Wafer 10 formed of 4H-SiC single crystal or 6H-SiC single crystal can be chemically mechanically polished (CMP) and has a diameter of 150 mm and a thickness of 0.5 mm. Wafer 10 can be oriented "on-axis", that is, wherein its face 12 is perpendicular to the hexagonal c-axis. Slicing, grinding and polishing of wafer 10 can be performed according to known manufacturing techniques.

[0040] The light transmission and reflection associated with the optical device 16 can be measured in the VIS-IR range using a Cary 7000 Universal Measurement Spectrophotometer (UMS). The mathematical form for calculating the optical parameters according to the present disclosure can be as described below in conjunction with equations (A1 a) to (A7):

[0041] 4H-SiC and 6H-SiC are hexagonal uniaxial crystals. In such crystals, the optical axis coincides with the crystallographic hexagonal c-axis. When a beam is incident perpendicular to the c-plane of such a crystal, its polarization is always perpendicular to the optical axis. That is, such a beam is an ordinary beam, and its propagation is governed by the ordinary refractive index n0. Using equation (3) and Table 1 for n0 from Xu (cited above) and substituting T = 300K, an expression for n0(λ) at room temperature can be obtained:

[0042] For 4H-SiC:

[0043] For 6H-SiC:

[0044] For a beam incident perpendicular to the c-plane of a hexagonal uniaxial crystal, the reflectivity (R) is expressed as:

[0045]

[0046] The light transmission and reflection of a plate with parallel surfaces is calculated by taking into account multiple reflections at the front and back interfaces of the plate. This approximation yields a value for the measured transmission (T mes ) and reflection (R mes). See Pankove J., Optical Processes in Semiconductors, Dover Publ. NY 1971, p. 93; F. Soler, Multiple Reflections in an Approximately Parallel Plate, Opt. Comm. 139 (1997) 165-169.

[0047]

[0048]

[0049] In equations (A3) and (A4), α is expressed in cm -1 is the absorption coefficient in cm, and d is the plate thickness in cm. If the value of reflectivity R is known, equation (A3) can be analyzed with respect to α as follows:

[0050]

[0051] The transmission and reflection in the extreme case of a completely transparent plate can be obtained by substituting a=0 into equations (A3) and (A4) as follows:

[0052]

[0053]

[0054] The light absorption coefficient of SiC single crystal is measured by the transmission (T mes ) and reflectivity (R) are calculated by equation (A5). The R value is calculated using equation (A2) from the refractive index dispersions (A1a) and (A1b) of 4H and 6H determined by Xu.

[0055] In addition to light transmission and reflection, a sensitivity of 1·10 5 Ωcm to 1·10 12 The resistivity of SiC single crystals was measured at room temperature using the non-contact instrument COREMA-W with Ωcm. The temperature dependence of the resistivity in the temperature range of 25°C to 400°C was measured using the temperature-variable non-contact resistivity meter COREMA-VT, and the electrical conductivity (E A ) activation energy value. When the chip resistivity exceeds 1·10 12 In the case of Ωcm, by using E A The room temperature resistivity was estimated by extrapolating the resistivity to T = 300 K. The resistivity of all SiC crystals in this study is 1·10 6 Ωcm to 1.10 14 Ωcm.

[0056] Transmission curves 50(T) measured in the visible range from 0.35 μm to 0.80 μm on several high-resistivity vanadium-compensated 4H-SiC wafers mes @0°AOI) and reflection curve 52 (R mes @6°AOI) is shown in Figure 4 Transmission curves 54 (T) measured in the visible range from 0.35 μm to 0.80 μm on several high-resistivity vanadium-compensated 6H-SiC wafers mes @0°AOI) and reflection curve 56 (R mes @6°AOI) is shown in Figure 5 middle.

[0057] Examples of absorption spectra α(λ) calculated using equation (A5) for two wafers, one high resistivity 4H-SiC (line 60) and one high resistivity 6H-SiC (line 58) in the visible range are shown in Figure 6 These absorption curves 60, 58 show two distinct absorption regions: a steep rise in absorption below about 0.40 μm for the 4H crystal and a steep rise in absorption below about 0.44 μm for the 6H crystal. This absorption increase is believed to be due to the fundamental cutoff, i.e., the transition from the valence band to the conduction band. Its slope is proportional to λ due to the indirect nature of the hexagonal SiC band gap and the phonon-assisted electronic transition. -2 See Sridhara et al., Absorption Coefficient of 4H Silicon Carbide from 3900 to 3250A, J. Appl. Phys. Vol. 84, No. 5 (1998) 2963-2964

[0058] like Figure 6 As shown in , there is a near-band edge absorption “shoulder” between 0.45 μm and 0.7 μm, where its amplitude is about 0.01 cm at λ ≈ 0.7 μm. -1 To about 1Gm at λ≈0.45μm -1 This residual absorption is commonly observed in wide-bandgap semiconductors and is usually attributed to electronic transitions involving unassigned shallow energy levels such as crystal defects or impurities. The optical absorption at wavelengths beyond λ ≈ 0.7 μm is very low, below 0.1 cm -1 .

[0059] Although all vanadium-compensated SiC crystals in this study were optically transmissive, their transmittance showed significant variation. An example of such variation is shown in Figure 7 middle, Figure 7The light transmission in the VIS-NIR range measured on six different vanadium compensated 6H-SiC wafers is shown. The two curves 66 with the lowest transmission were measured on two Nu-type 6H wafers. (Nu-type refers to the type of compensated SiC crystal in which shallow donors (nitrogen) dominate over shallow acceptors (Al+B).) The resistivity of the Nu-type wafers is between 9·10 9 Ωcm to 2·10 11 In the range of Ωcm.

[0060] Figure 7 The two curves 62 (one solid and one dashed) with the highest transmittance in FIG. 6 represent two Pi-type wafers. (Pi-type means a type of compensated SiC crystal in which shallow acceptors (in this case Al) dominate over shallow donors (N).) The resistivity of these wafers is 1·10 6 Ωcm to 1·10 7 Ωcm.

[0061] Figure 7 The two curves 64 in FIG. 6 show the light transmission of two Pi-type 6H-SiC wafers containing boron (shallow acceptor) at a concentration exceeding that of N (shallow donor). The resistivity of these wafers is 1·10 12 Ωcm to 1·10 14 Ωcm.

[0062] The light absorption in the visible range calculated using equation (A5) for several 4H-SiC wafers and 6H-SiC wafers with different doping and resistivity is shown in Figure 8 and Fig. 9 middle.

[0063] Depend on Figure 8 and Fig. 9 The strongest absorption shown by lines 68 and 76 in the figure is the absorption of the Nu-type wafer with nitrogen dominating in a light impurity background. The resistivity of the 4H wafer is 1·10 11 Ωcm, while the resistivity of 6H wafer is 1·10 9 For these wafers, light absorption is highest not only in the visible range, but also in the infrared.

[0064] Slightly lower light absorption, as shown by lines 70 and 77, is also for the Nu-type wafers. However, these wafers have a 5·10 12 The higher resistivity of Ωcm and 5·10 10 Higher resistivity of Ωcm.

[0065] Figure 8 and Fig. 9Lines 72, 74 and 78 in FIG. 7 represent the light absorption measured on a Pi-type wafer in a light impurity background dominated by boron. The resistivity of the 4H wafer is 1·10 13 Ωcm (line 72) and 1·10 14 Ωcm (line 78). The resistivity of the 6H wafer is 1·10 11 Ω cm (line 78). The absorption in these wafers is confined to the band edge shoulder and does not extend into the infrared.

[0066] The lowest light absorption is given by Fig. 9 The curves 80 and 82 in FIG. are shown. They are measured on two Pi-type 6H-SiC wafers with Al dominance in a light impurity background. The wafer has 1·10 5 Ωcm and 1·10 7 Relatively low resistivity of Ωcm.

[0067] The relationship between the light absorption of vanadium-compensated SiC crystals, their type, doping and resistivity is given in the following Table 1. In the last column the light absorption coefficient determined in infrared light at λ=2.5 μm is added.

[0068] Table 1

[0069]

[0070]

[0071] The obtained data can be used as a guide for selecting certain types of vanadium compensated high-resistivity SiC single crystals for applications in the field of transmission optics in the visible and near-infrared spectral range.

[0072] Both vanadium compensated high resistivity 6H and 4H polytype SiC single crystals are suitable for demanding applications in transmission optics in the wavelength range from 420 nm in the visible to about 4.5 μm in the infrared, especially if their doping and resistivity are optimized.

[0073] Due to the wider band gap, vanadium compensated 4H-SiC single crystals are preferred for optical applications at shorter wavelengths below 450 nm.

[0074] If the resistivity of the vanadium-compensated Nu-type SiC single crystal is lower than 1·10 10 Ωcm, for 4H less than 1·10 12 Ωcm, it cannot be used for demanding optical applications. The optical loss of such a crystal in the visible range will be close to 1cm -1 , the optical loss in the infrared will be as high as 0.1cm -1 .

[0075] If the resistivity of the vanadium-compensated Nu-type SiC single crystal is greater than 1·10 11 Ωcm, for 4H greater than 5·10 12 Ωcm, it can be used for infrared optical applications. For such a crystal, the light absorption in the infrared will be less than 0.01cm -1 .

[0076] If the resistivity of the vanadium-compensated Pi-type SiC single crystal in a boron-dominated light impurity background is greater than 1·10 11 Ωcm, for 4H greater than 1·10 13 Ωcm, it can be used for infrared optical applications. For such a crystal, the light absorption in the infrared will be less than 0.01cm -1 .

[0077] If the resistivity of the vanadium-compensated Pi-type SiC single crystal in a light impurity background dominated by boron is greater than 1·10 13 Ωcm, for 6H greater than 5·10 11 Ωcm, then it can be used for optical applications in the visible light range. For such a crystal, the light absorption should be lower than 0.8cm at λ = 450nm. -1 , should be less than 0.01cm at λ = 750nm -1 .

[0078] If the resistivity of the vanadium-compensated Pi-type 6H-SiC single crystal in the presence of aluminum in a light impurity background is 1·10 5 Ωcm to 1·10 8 Ωcm, they can be used for demanding optical applications. Such crystals can provide optimal transmittance in the visible light range. Their light absorption should be less than 0.8 cm at λ = 450 nm. -1 , should be less than 0.01cm at λ = 750nm -1 . Their near-band-edge absorption shoulders are lower and narrower than those of all other crystal types.

[0079] In addition, large, industrial-sized silicon carbide (SiC) single crystals can be grown from the vapor phase by a sublimation technique commonly referred to as physical vapor transport (PVT). In this technique, a silicon carbide source, which may be in the form of silicon-carbon powder or grains, can be provided in a high temperature region of a crucible. Silicon carbide seeds, such as 4H polytype or 6H polytype single crystal silicon carbide plates or wafers, can be positioned in a lower temperature region of the crucible. The crucible can be heated to sublimate the silicon carbide source and fill the crucible with the gaseous products of the sublimation. The resulting vapor migrates to the cooler silicon carbide seeds and deposits on the seeds to grow silicon carbide pear-shaped crystals of the desired polytype, diameter, and thickness.

[0080] During sublimation growth, the silicon carbide crystal may be exposed to various impurities present in the growth system, and such exposure may result in the formation of an impurity background in the crystal. Background impurities found in silicon carbide crystals include boron and nitrogen, which may be present in concentrations as high as n·10 16 cm -3 In silicon carbide crystals grown by sublimation, graphite can be a source of boron and nitrogen background impurities.

[0081] The optical properties of bulk silicon carbide single crystals grown by sublimation have been studied, and the overall optical absorption properties of pure, undoped or otherwise unintentionally doped hexagonal silicon carbide crystals are described in Singh et al., "Nonlinear optical properties of hexagonal silicon carbide", Appl. Phys. Lett, Vol. 19, 2 (1971) 53-56. The description shows that the substantially transparent region of silicon carbide crystals of this nature extends from the band edge cutoff (about 380 nm for 4H and about 410 nm for 6H) to λ≈4 μm in the infrared, where it terminates in a multiphonon absorption band. The size of the near-band edge absorption shoulder is about 1 cm -1 , which is typical for undoped 4H-SiC and 6H-SiC crystals.

[0082] As discussed in Scajev et al., "Application of a Time-Resolved Four-Wave Mixing Techniquefor the Determination of Thermal Properties of 4H-SiC Crystals." J..Phys.D.Appl.Phys.42(5):055413, Feb.2009 and Tarekegne et al., "Investigation of the Absorption Mechanisms of SiC for Lighting Applications", 6th International Workshop on Wideband Semiconductor Materials & Devices, Fujian, China, 2018, sublimation-grown SiC heavily doped with boron, nitrogen, and aluminum up to 10 18 cm -3Optical properties of 4H silicon carbide single crystals and 6H silicon carbide single crystals of or higher. Each of these impurities produces a specific near-band edge absorption band in the visible light range. The light absorption band peak associated with boron is at about 430nm to 480nm for 4H-SiC and at about 450nm to 510nm for 6H-SiC. The absorption shoulder associated with aluminum is at about 410nm to 420nm and is very close to the band edge cutoff. The absorption band associated with nitrogen is at about 460nm to 470nm in 4H and at about 620nm to 630nm in 6H. .

[0083] Although some optical transparency has been observed in these crystals, their optical applications have been found to be very limited, primarily due to optical absorption that may be caused by residual impurities. One way to minimize near-band edge absorption in sublimation-grown 4H polytype SiC crystals and 6H polytype SiC crystals is to reduce the presence of unwanted background impurities. However, given the high temperatures of the PVT growth process and the use of graphite as the crucible material, reducing the boron and nitrogen background impurities in PVT-grown SiC single crystals to less than 1·10 15 cm -3 The level can be considered at least challenging, even if unrealistic.

[0084] According to the present disclosure, 4H polytype or 6H polytype silicon carbide crystals can have high optical transparency in the visible spectrum. Silicon carbide crystals showing these characteristics or similar characteristics can be used in various optical applications, such as but not limited to optical windows, lenses and optical waveguides operating at wavelengths of about 410nm to about 750nm. Sublimation physical vapor transmission (PVT) technology can be used to grow optically transparent 4H silicon carbide crystals and 6H silicon carbide crystals. In one form, silicon carbide single crystals are doped with aluminum and contain residual boron and nitrogen impurities. On the one hand, the aluminum dopant exists in a concentration exceeding the combined concentration of residual nitrogen and boron impurities, otherwise it is lower than the level that may cause the crystal growth to be unstable. Although it is not intended to be bound by any particular theory, it is believed that the aluminum dopant reduces the size of the near-band edge light absorption related to the presence of boron and nitrogen impurities. Similarly, keeping the lowest possible concentration of background boron and nitrogen impurities can also reduce light absorption.

[0085] As described above, sublimation techniques can be used to grow silicon carbide single crystals, including silicon carbide single crystals of 4H polytypes and 6H polytypes. On the one hand, these techniques can be designed to reduce or remove boron and nitrogen impurities in or from the growth system. For example, the presence of background boron can be reduced by using halogen-purified graphite parts (including but not limited to growth crucibles). In one form, the halogen purification of graphite parts can include heating graphite parts in a furnace chamber with an atmosphere containing chlorine, fluorine, or both chlorine and fluorine. At high temperatures, the carbon-bound boron present in graphite reacts with gaseous halogens such as chlorine and fluorine and forms volatile halides such as BCl3 and BF3. The volatile halides can be removed from the furnace chamber by an inert gas flow through the furnace chamber. After the purification, the graphite parts may still contain residual boron at a concentration of about 10 ppb by weight to about 100 ppb by weight. Similarly, the silicon carbide crystals grown by sublimation of these purified graphite parts may still contain about 10 15 cm -3 Up to 10 16 cm -3 The concentration of residual boron impurities.

[0086] Reducing or removing nitrogen impurities in or from the growth system may include performing a pre-growth high temperature bake of the crystal growth hot zone in a vacuum. Alternatively, sublimation crystal growth may be performed under a flow of ultra-high purity argon. Silicon carbide crystals grown under these conditions may still contain a concentration of about 10 15 cm -3 Up to 10 16 cm -3 of residual nitrogen impurities.

[0087] Considering that even if steps are taken to reduce or remove impurities, some residual boron and nitrogen impurities may still remain, near-band edge light absorption may still exist due to their presence. However, as described above, the addition of aluminum dopants can be used to reduce the near-band edge light absorption caused by the presence of boron and nitrogen impurities. Similar to boron, aluminum is a shallow acceptor in 4H-SiC and 6H-SiC. In the SiC gap, the energy level of aluminum is located about 0.2 eV above the valence band maximum (see, for example, Atabaev et al., "Spectral Dependence of Optical Absorption of 4H-SiC Doped with Boron and Aluminum", J. Spectroscopy (2018) Article ID 8705658 and online NSM Archive-Silicon Carbide (SiC)-Impurities and Defects). The lowest energy level of the boron acceptor is about 0.35 eV above the valence band edge and is higher than the energy level of aluminum. As an acceptor, aluminum can combine with boron to compensate for the nitrogen (donor). If aluminum is introduced in sufficient concentration so that N A1 +N B >N N , then all electrons are stripped from the nitrogen energy levels and thus no electrons are present at the bottom of the conduction band. Thus, nitrogen-related light absorption can be reduced or eliminated.

[0088] Doping with aluminum causes a redistribution of charge in the SiC crystal, which is reflected by a shift in the Fermi level position closer to the aluminum level. Al >N B +N N , the Fermi level will move to a position lower than the lowest energy level of boron, thereby reducing or eliminating the electron population present at the boron energy level. Therefore, the light absorption associated with boron can be reduced or eliminated.

[0089] Considering the above, in order to “reduce” both the boron acceptor and the nitrogen donor from electrons, as shown in Equation (1), the concentration of the aluminum dopant (N Al ) exceeds the residual boron (N B ) and nitrogen (N N ) combined concentration:

[0090] N Al >N B +N N (1)

[0091] Doping with aluminum may result in aluminum-related light absorption, but any such absorption band will be very close to the band edge cutoff and will actually merge with it.

[0092] In aluminum-doped 4H and 6H SiC polytypes, aluminum replaces silicon. The covalent radius of aluminum is The covalent radius of silicon is Considering the large radius of aluminum, the dissolution of aluminum in the silicon carbide crystal may cause local expansion and stress in the crystal lattice. At a certain concentration of aluminum, the formation of crystal defects, improperly oriented grains, and foreign polytypes may occur during the growth of the silicon carbide crystal. By keeping the concentration of aluminum below a certain level (e.g., about 5·10 17 cm -3 ) can avoid these problems, although variations are possible.

[0093] Although aluminum-doped silicon carbide single crystals can be grown by adding aluminum carbide (Al4C3) directly to a silicon carbide solid source, Al4C3 is unstable at high temperatures and may undergo decomposition into solid carbon and Al+C liquid through a peritectic reaction, where the partial pressure of gaseous aluminum over the liquid exceeds 100 Torr. Therefore, there may be an initial peak in aluminum concentration in the crystal followed by rapid consumption of the aluminum source.

[0094] U.S. Patent No. 8,216,369, the contents of which are incorporated herein by reference in their entirety, relates to more spatially uniform doping in a PVT process. For example, it discloses a growth method that includes a doping slow-release container loaded with a dopant and contained within a growth crucible. Fig.10 , schematically illustrates a system 110 for sublimation growth of an aluminum-doped silicon carbide crystal having a more spatially uniform aluminum concentration throughout the crystal. The system 110 includes a chamber 112 in which a growth crucible 114 is positioned.

[0095] The crucible 114 is sealed by a lid 116 and surrounded by thermal insulation 118. A heating element 120 is positioned around the chamber 112 and is configured to provide heat to the crucible 114. The heating element 120 may be an RF coil or a resistive heating element, although other variations are possible.

[0096] Within the crucible 114, a SiC source 122 and a SiC seed crystal 124 are arranged in a spatial relationship suitable for PVT crystal growth. More specifically, the SiC seed crystal 124 can be positioned near the top of the crucible 114 and can be, for example, attached or coupled to the lid 116, and the SiC source 122 can be positioned below the SiC seed crystal 124. The SiC source 122 is housed in a crucible 126 supported by a support structure 128. The support structure 128 includes a first member 130 spaced apart from a second member 132, and the first member 130 and the second member 132 extend from a lower portion of the crucible 114 toward the lid 116. In this arrangement, the crucible 126 and thus the SiC source 122 positioned in the crucible 126 are positioned above the lower portion of the crucible 114 with a free space 134 positioned therebetween. The first member 130 includes a hole 136 and the second member 132 includes a hole 138. Holes 136, 138 provide fluid communication between free space 134 and a space located between crucible 126 and crucible 114, such as Fig.10 The direction is indicated by arrow A.

[0097] When the crucible 114 is heated by the heating element 120 during the sublimation growth of the crystal, the SiC source 122 vaporizes and fills the interior of the crucible 114 with a Si-containing and C-containing vapor that flows toward the SiC seed crystal 124 as shown by the directional arrow B. The Si-containing and C-containing vapor may contain volatile molecular species, such as Si, Si2C, and SiC2. A vertical temperature gradient may be established on the crucible 114, wherein the temperature of the lower portion of the crucible 114 is higher than the temperature of the upper portion of the crucible 114 (e.g., near the lid 116). A vertical temperature gradient of this nature generates a driving force for vapor transport as shown by the directional arrow B. The vapor transport brings vapor nutrients from the SiC source 122 to the SiC seed crystal 124. Once reaching the SiC seed crystal 124, the supersaturated vapor is deposited on the SiC seed crystal 124, thereby causing the growth of a SiC single crystal 140 on the SiC seed crystal 124.

[0098] A slow-release doping container 142 that can be used for aluminum doping is positioned in the free space 134 in the crucible 114. The doping container 142 includes an internal space or chamber for receiving and holding a dopant source 144. In one form, the dopant source 144 is an aluminum dopant source and can be in the form of a solid aluminum compound having a low decomposition pressure at the SiC sublimation growth temperature. For example, in one form, the decomposition pressure can be less than about 1 Torr, although other variations are also possible. Non-limiting examples of solid aluminum compounds that can be used include oxygen-containing aluminum compounds, such as but not limited to aluminum carbonate, aluminum silicate, and aluminum oxide. In a specific but non-limiting form, the solid aluminum compound is aluminum oxide (Al2O3), which is also referred to as aluminum oxide. Aluminum oxide can be provided in the form of pre-melted aluminum oxide "cracks", such as pure, undoped sapphire sheets. In general, the amount of dopant source 144 contained in the doping container 142 can be sufficient to support aluminum doping throughout the crystal growth cycle.

[0099] During the crystal growth cycle, the crucible 114 is heated and as the temperature of the crucible 114 increases to as high as about 2000°C, the oxygen-containing aluminum compound undergoes a chemical transformation that ultimately produces solid aluminum oxide. As the temperature of the crucible 114 further increases and reaches and exceeds the melting point of aluminum oxide of about 2040°C, the aluminum oxide melts and fills the interior of the doping vessel 142 with a vapor that is a product of evaporation and decomposition of the aluminum oxide melt. The vapor may contain molecules of Al2O3, Al2O, AlO, Al, and O. At the melting point of aluminum oxide, the total vapor pressure above the melt is about 0.01 Torr, while at 2200°C, it is less than 0.1 Torr. Similarly, if the temperature of the SiC sublimation growth process does not exceed about 2400°C, the vapor pressure of the molten aluminum oxide should not exceed about 1 Torr.

[0100] The doping vessel 142 includes a capillary channel, further details of which will be described below in conjunction with Fig.11 As discussed, the vapor containing aluminum and oxygen escapes from the doping vessel 142 through the capillary passage and migrates within the crucible 114, as shown in FIG. Fig.10 As shown by the direction arrow C in FIG. During the migration process, these vapors can contact and react with the carbon of graphite to form elemental aluminum vapor and carbon monoxide gas. Eventually, the aluminum vapor can reach the silicon carbide crystal growth interface and adsorb on the interface, thereby causing aluminum to dope the growing silicon carbide crystal.

[0101] Doping vessel 142 may be formed of one or more materials that provide stability in the high temperature environment of silicon carbide sublimation growth and resistance to attack by molten alumina and highly corrosive silicon and carbon containing vapors. Fig.11In one non-limiting form, the doping vessel 142 is formed of an outer component 146 and an inner component 148, with the outer component 146 formed or positioned on or around the inner component 148. The outer component 146 may be at least partially formed of a first material, and the inner component 148 may be at least partially formed of a second, different material.

[0102] exist Fig.11 In the illustrated form, the external component 146 is in the form of a crucible 150 including a lid 152. Since the crucible 150 and the lid 152 can be positioned in the free space 134 and thus can be exposed to the silicon- and carbon-containing vapor released by the SiC source 122, the crucible 150 and its lid 152 can be at least partially formed of a material that is stable to the corrosion of the silicon- and carbon-containing vapor that may be present in the crucible 114. For example, at least the outer surface that may be in contact with the silicon- and carbon-containing vapor can be formed of a material that is stable to the corrosion of the silicon- and carbon-containing vapor. Non-limiting examples of materials that can provide stability of this nature include graphite, carbides of refractory metals such as tantalum carbide (TaC) or niobium carbide (NbC), and graphite coated or layered with refractory carbides. In a specific but non-limiting form, the crucible 150 and its lid 152 can be formed of dense fine-grained graphite.

[0103] exist Fig.11 In the illustrated form, the internal assembly 148 is in the form of a crucible 154 including a lid 156. For example, the lid 152 of the crucible 150 may be removed to facilitate positioning of the crucible 154 and its lid 156 in the crucible 150, and the lid 152 may be reengaged with the crucible 150 to secure the crucible 154 and the lid 156 in the crucible 150. Because the crucible 154 and the lid 156 include an interior space or chamber for receiving and holding the dopant source 144 (which may be, for example, an aluminum dopant source), and in turn may be exposed to molten aluminum oxide and to aluminum-containing vapors released by the dopant source 144, the crucible 154 and its lid 156 may be at least partially formed of a material that is stable to or resistant to corrosion or damage by the molten aluminum oxide or the aluminum-containing vapors. For example, at least the inner surfaces of the crucible 154 and the lid 156 that are disposed toward the dopant source 144 may be formed of a material that is stable to or resistant to corrosion or damage by the molten aluminum oxide or the aluminum-containing vapors. Non-limiting examples of materials that can provide stability of this nature include refractory metals or metal alloys such as, but not limited to, tantalum, molybdenum, tungsten, rhenium, or alloys thereof. In one specific but non-limiting form, the crucible 154 and its lid 156 can be formed of tungsten.

[0104] Although the doping vessel 142 has been described as being formed of separate inner and outer components formed of different materials, it should be understood that the doping vessel 142 may also be made of a single component having a composite structure formed of different materials. For example, the different materials may be present in separate layers, where one layer of a first material is deposited on a second layer formed of a separate material. For example, in the case of the crucible 154 and the lid 156, these components may be formed of a first material and then a second material may be coated or affixed to their outer surfaces to provide a composite structure with the crucible 154 and the lid 156. Fig.11 The structure shown is similar to the structure shown, although other variations are possible.

[0105] As described above, the doping vessel 142 includes a capillary passage 158 through which a vapor containing aluminum and oxygen escapes from the doping vessel 142 when the aluminum oxide melts. The capillary passage 158 is formed by a hole 160 through the lid 152 and a hole 162 through the lid 156. The rate at which the vapor containing aluminum and oxygen can escape or be released from the doping vessel 142 can be controlled at least in part by the temperature at which the aluminum oxide melts and the size of the holes 160, 162. For example, when the temperature at which the molten aluminum oxide is maintained is higher and the size of the holes 160, 162 is larger, a higher rate at which the vapor containing aluminum and oxygen escapes or is released from the doping vessel 142 can occur. In some forms, the size of the holes 160, 162 can be the same or different, with one or both having a diameter in the range of about 0.1 mm to about 1.5 mm.

[0106] The use of doping vessel 142 can, for example, facilitate the production of sublimation-grown silicon carbide single crystals containing a spatially uniform concentration of aluminum dopant throughout the crystal. The above techniques can also similarly avoid the situation where a high aluminum concentration is present in the first grown pear-shaped crystal portion of the crystal followed by rapid consumption of the aluminum source. In addition, the aluminum dopant concentration can be controlled so that it exceeds the combined concentration of residual boron and nitrogen while remaining below a level that causes crystal defects (e.g., about 5.10 17 cm -3 ).

[0107] Embodiment 1: Four aluminum-doped SiC single crystals, two 4H polytypes and two 6H polytypes, were grown by sublimation. For comparison purposes, two additional SiC pear-shaped crystals, one 4H polytype and one 6H polytype, were grown by sublimation without aluminum doping. The experimental conditions for sublimation growth disclosed below are provided with reference to the above-described system 110.

[0108] Prepare similar to Fig.11The doping container 142 of the doping container. The doping container includes an inner crucible and a lid corresponding to or similar to the crucible 154 and the lid 156, made of pure tungsten available from Plansee USA LLC, 115 Constitution Boulevard, Franklin, MA 02038. The inner crucible has the following dimensions: 25 mm OD×15 mm ID×25 mm high. The lid is 5 mm thick and has a single through hole of 1.0 mm diameter drilled in its center. The outer crucible and lid corresponding to the crucible 150 and the lid 152 are made of halogen-purified dense isostatic graphite grade IG-11 available from Toyo Tanso USA Inc., 2575 NW Graham Cir, Troutdale, OR 97060. The outer crucible has the following dimensions: 32 mm OD×25 mm ID×30 mm high. The graphite lid is 5 mm thick and has a 1.0 mm diameter hole drilled in its center. The inner crucible fits tightly inside the outer graphite crucible.

[0109] A total weight of 7 grams of pure pre-melted sapphire cracked pieces was loaded into the inner crucible of the slow release container. A graphite growth crucible and lid similar to or corresponding to crucible 114 and lid 116 were made from halogen-purified dense isostatic graphite grade IG-11 available from Toyo Tanso USA Inc., 2575 NW Graham Cir, Troutdale, OR 97060. Prior to its use in crystal growth, the crucible and lid were halogen purified to an ash rating of less than 5 ppm by weight. The boron content in the purified graphite was determined to be 30 ppb by weight by impurity analysis using a glow discharge mass spectrometer (EAG LLC, 4747 Executive Drive, Suite 700, San Diego, CA 92121).

[0110] A doping container is loaded at the bottom of a graphite growth crucible, and a source crucible containing a SiC source corresponding to or similar to crucible 126 is loaded into the graphite growth crucible. The source crucible is placed on a support so that a free space is formed to accommodate the doping container. A SiC seed crystal is attached to the lid of the graphite growth crucible and the graphite growth crucible is sealed with the lid. The SiC seed crystals are 4H-SiC and 6H-SiC wafers with a diameter of 150 mm. The 4H-SiC seed crystal is oriented with its growth surface facing the <000-1> crystallographic direction. The 6H-SiC seed crystal is oriented with its growth surface facing the <0001> crystallographic direction.

[0111] The loaded graphite growth crucible was placed into a furnace chamber where it was surrounded by thermal insulation. The chamber was evacuated and the RF coil was powered to heat the graphite growth crucible to an initial temperature of 1400°C. At this temperature and under continuous pumping, the growth system was immersed for 24 hours to achieve the deepest possible degassing and reach 1·10 -6 The chamber was filled with UHP argon containing less than 10 ppb residual N2 to a pressure of 5 Torr, and a UHP argon flow of 300 sccm was established throughout the chamber.

[0112] The graphite growth crucible was then heated to a sublimation growth temperature. More specifically, the graphite growth crucible was heated to reach a temperature of 2180°C at the top of the crucible and a temperature of 2210°C at the bottom of the crucible. The top and bottom temperatures were measured and monitored with an optical pyrometer. The graphite growth crucible was immersed at the above temperatures for a predetermined period of time and then cooled to room temperature.

[0113] After the growth run is completed, the grown SiC crystal pears are recovered and fabricated into 150 mm diameter x 500 micron thick wafers according to SEMI standards. The wafers are first mechanically polished and then polished using a final CMP polish.

[0114] Embodiment 2: The optical properties of the wafer produced in Example 1 were evaluated. The evaluation included measurement of its light transmission and reflection. Non-polarized light was measured in the wavelength range of 350nm to 850nm using a spectrophotometer (Agilent Cary 7000UMS). During the measurement of transmission, the angle of incidence (AOI) was 0°. During the measurement of reflection, the AOI was 6°. As outlined in Optical Processes in Semiconductors, JI Pankove, Dover Publ, NY, 1971, pages 93 to 94, the light absorption coefficient (α, em) was calculated from the data on transmission and reflection using the approximation of a plate with parallel surfaces, thickness d and an infinite number of internal reflections. -1 ).

[0115] The wavelength dispersion (α, cm-1) of light absorption measured for some 4H-SiC wafers is Fig.12 The wavelength dispersion (α, cm) of the light absorption measured for some 6H-SiC wafers is shown in -1 )exist Fig.13 Shown in. Fig.12 and Fig.13The curves of show the absorption coefficients of wafers doped with aluminum (lower curve) and wafers not doped with aluminum (upper curve). After the optical measurements, some of the measured wafers were cut into small pieces and the fragments were sent for N, B and Al impurity analysis by secondary ion mass spectrometry (SIMS) (EAG LLC, 4747 Executive Drive, Suite 700, San Diego, CA 92121). The results of the SIMS impurity analysis are shown in Table 2. Measures aimed at reducing background B and N contaminants include the use of halogen-purified graphite and extended hot zone vacuum baking, resulting in B and N levels in the grown SiC crystals below 1·10 16 cm -3 The results of the light absorption coefficient measurements are also shown in Table 2. The SiC crystals in the last two rows of Table 2 were grown without deliberate aluminum doping and are shown in the table for comparison. The results obtained show that by aluminum doping, a greatly reduced light transmission in the visible spectral range is achieved.

[0116] Table 2

[0117]

[0118]

[0119] What is described above is an example. The present disclosure is intended to cover changes, modifications and variations of the subject matter described herein that fall within the scope of the present application including the appended claims. As used herein, the term "comprising" means including but not limited to. The term "based on" means at least partially based on. In addition, in the case where the present disclosure or claims record the indefinite article "a", "an", "a first", or "another" element or its equivalent, it can be interpreted as including one or more than one such element, neither requiring nor excluding two or more such elements.

Claims

1. A composition comprising: Vanadium compensated high resistivity 6H polytype or 4H polytype silicon carbide SiC single crystal; wherein the SiC single crystal is configured to transmit light having a wavelength in the range of 420 nm to 4.5 μm, and wherein the concentration of aluminum in the SiC single crystal is greater than the total concentration of boron and nitrogen in the crystal; and The concentration of nitrogen in the silicon carbide SiC single crystal is less than or equal to 1.10 16 cm -3 , The light absorption coefficient of the SiC single crystal at a wavelength in the range of 400 nm to 800 nm is less than 0.4 cm -1 . 2 . The composition according to claim 1 , wherein the SiC single crystal is a vanadium-compensated 4H—SiC single crystal, and wherein the wavelength of the light is less than 450 nm.

3. The composition according to claim 1, wherein the SiC single crystal is a vanadium-compensated 6H polytype Nu-type SiC single crystal, and has a relative humidity greater than or equal to 1·10 10 Resistivity of Ωcm.

4. The composition according to claim 1, wherein the SiC single crystal is a vanadium-compensated 4H polytype Nu-type SiC single crystal, and has a relative humidity greater than or equal to 1·10 12 Resistivity of Ωcm.

5. The composition according to claim 1, wherein the SiC single crystal is a vanadium-compensated 6H polytype Nu-type SiC single crystal, and has a relative humidity greater than 1·10 11 The resistivity is Ωcm, and wherein the wavelength of the light is infrared.

6. The composition according to claim 1, wherein the SiC single crystal is a vanadium-compensated 4H polytype Nu-type SiC single crystal, and has a relative humidity greater than 5·10 12 The resistivity is Ωcm, and wherein the wavelength of the light is infrared.

7. The composition according to claim 1, wherein the SiC single crystal is a 6H polytype Pi-type SiC single crystal of vanadium compensation in a light impurity background dominated by boron, and has a relative humidity greater than 1·10 11 The resistivity is Ωcm, and wherein the wavelength of the light is infrared.

8. The composition according to claim 1, wherein the SiC single crystal is a 4H polytype Pi-type SiC single crystal compensated by vanadium in a light impurity background dominated by boron, and has a relative humidity greater than 1·10 13 The resistivity is Ωcm, and wherein the wavelength of the light is infrared.

9. The composition according to claim 1, wherein the SiC single crystal is a 4H polytype Pi-type SiC single crystal compensated by vanadium in a light impurity background dominated by boron, and has a relative humidity greater than 1·10 13 Resistivity of Ωcm.

10. The composition according to claim 1, wherein the SiC single crystal is a 6H polytype Pi-type SiC single crystal of vanadium compensation in a light impurity background dominated by boron, and has a relative humidity greater than 5·10 11 Resistivity of Ωcm.

11. The composition according to claim 1, wherein the SiC single crystal is a vanadium-compensated Pi-type 6H-SiC single crystal in a light impurity background dominated by aluminum, and has a 5 Ωcm to 1·10 8 Resistivity of Ωcm.

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