SiC power device technology has over the past years continued to gain massive interest in automotive and industrial applications. Most devices are today fabricated on 150 mm diameter substrates while the 200 mm diameter substrates are still at early stage in both development and in terms of mass production. In this paper, we report the latest progress on STMicroelectronics 200 mm diameter crystals and substrates. To handle the mechanism behind the crystal growth process you need to control the temperature and pressure in the customized graphite growth chamber. We detail the methods that allow to characterize the quality of the ingot by monitoring the relevant properties both related to the grown crystal and to the produced substrate. We also describe the key parameters to be controlled on the substrate to be sure it is suitable for device making (i.e. mechanical behavior, resistivity, surface roughness, effectiveness of the surface preparation).

Spin-active color centers in solids show good performance for quantum technologies. Several transition-metal defects in SiC offer compatibility with telecom and semiconductor industries. However, whether their strong spin-orbit coupling degrades their spin lifetimes is not clear. We show that a combination of a crystal-field with axial symmetry and spin-orbit coupling leads to a suppression of spin-lattice and spin-spin interactions, resulting in remarkably slow spin relaxation. Our optical measurements on an ensemble of Mo impurities in SiC show a spin lifetime T-1 of 2.4 s at 2 K.

Color centers in wide-bandgap semiconductors are attractive systems for quantum technologies since they can combine long-coherent electronic spin and bright optical properties. Several suitable centers have been identified, most famously the nitrogen-vacancy defect in diamond. However, integration in communication technology is hindered by the fact that their optical transitions lie outside telecom wavelength bands. Several transition-metal impurities in silicon carbide do emit at and near telecom wavelengths, but knowledge about their spin and optical properties is incomplete. We present all-optical identification and coherent control of molybdenum-impurity spins in silicon carbide with transitions at near-infrared wavelengths. Our results identify spin S = 1/2 for both the electronic ground and excited state, with highly anisotropic spin properties that we apply for implementing optical control of ground-state spin coherence. Our results show optical lifetimes of ~60 ns and inhomogeneous spin dephasing times of ~0.3 μ s, establishing relevance for quantum spin-photon interfacing.

X-ray topography shows that selective KOH etching after CVD growth of n-type epilayers on highly N doped 4H SiC substrates can be used to reliably map pure and mixed Threading Screw Dislocations (TSD). The influence of the mapping grid density and the wafer position in the crystal on the average TSD density are investigated. A reliable mapping of TSD contributed to the development of 100mm SiC wafers with average TSD density down to 200 cm-2.

Silicon Carbide (SiC) has long been considered a promising semiconductor material for high power devices, and has also recently found to be one of the emergent materials for quantum computing. Important for these applications are both the quality and purity of the crystal. In order to be able to engineer components (be it power devices or components for quantum computing), it is necessary to study and understand the behavior of various defects in the crystal.Deep level defects can greatly influence the semiconducting properties, since they can act as recombination centers by interacting with both holes from the valence band and electrons from the conduction band. Because of this, they may be used to control the charge carrier life time. Besides influencing the electric properties of the materials, deep level defects are also of interest in the field of quantum computing. In this application, the deep level defects can be used as basic units for quantum information – so called qubits.Deep level defects may also be classified based on their origin, i.e. impurity or intrinsic. An impurity consists of one or more foreign atoms, which means neither carbon nor silicon in the case of SiC. Impurities can be incorporated in the crystal during growth, or through implantation or diffusion. A defect is intrinsic when it does not involve foreign atoms, but instead imperfections in the perfect crystal structure, for example a vacancy, an anti-site or a combinations of these. Intrinsic defects can be created during growth or artificially, using for example electron irradiation.This thesis is focused on characterization of several deep level defects in SiC using different optical techniques. The optical transitions investigated are in the near-infrared region.Paper 1 focuses on the possibility to control the concentration of intrinsic defects through the cooling down procedure after high temperature annealing. The temperature of 2300°C is close to the bulk crystal growth temperature. It is shown that it is possible to control the concentration of the silicon vacancy (VSi) and UD-2 (later identified as the divacancy (VCVSi)) by the cooling sequence. Both these defects have later been shown to be promising candidates as qubits and single photon emitters.Paper 2 gives insight into the electronic structure of the unidentified deep level defect UD-4, which is believed to be of intrinsic origin. The defect is investigated in the polytypes 4H-, 6H-, and 15R-SiC, and the number of optical centers associated with UD-4 follows neither the number of inequivalent sites nor the possible configurations for pair-defects. There are two optical centers in 4H- and 6H-SiC, and three optical centers in 15R-SiC.Paper 3 investigates several transition metals incorporated in SiC and the formation energies for different possible configurations. This is of importance since several impurity related deep level defects cannot be explained as purely substitutional defects, based on the fact that the number of optical centers does not follow the number of inequivalent sites. This is investigated in detail, and explained using an asymmetric split vacancy (ASV) model. It was found that the formation energy for some transition metals in ASV are lower than the transition metal in a substitutional configuration. Further on, it was shown that the formation energies for transition metals in ASV configurations depend strongly on what kinds of inequivalent sites the ASV can be described by and the lowest formation energy that is found for transition metals in ASV occupying two hexagonal sites.In paper 4, the optical identification and electronic configuration of the commonly observed deep level defect tungsten (formerly known as UD-1) are reported. The electronic levels involved in the optical transitions of tungsten are deduced and described using group theory techniques.Paper 5 shows that the above mentioned ASV model can be used to describe the properties of niobium in SiC. In the paper, the optical identification and properties are analyzed and investigated experimentally using photoluminescence, photoluminescence excitation spectroscopy and Zeeman spectroscopy.In paper 6 the identification of molybdenum (formerly known as I-1) is reported including its electronic configuration. Molybdenum can be well described using the ASV model, and in this paper its local vibrational modes are also investigated in detail. It is shown that using the polarization dependence of local vibration replicas and a simplified defect molecule model, the estimated position of Mo in the ASV is in agreement with the theoretically predicted position reported in paper 3. The usefulness for molybdenum in SiC as a qubit is also investigated.In paper 7, two different intrinsic nearest pair-neighbor defects are reported: UD-2 (VCVSi) and UD-0 (tentatively assigned as the VCCSi). Their optical properties are analyzed together with their creation and annihilation properties.

Results from photoluminescence (PL) and Zeeman effect measurements of a PL center, labeled UD-1, in 6H SiC are presented. The spectrum consists of three no phonon-lines (NPLs) at 0.9952, 1.0015 and 1.0020 eV. The luminescence starts decreasing in intensity above 40 K and is completely quenched at 80 K. The observed Zeeman splitting reveals a spin one half of the ground state of the two highest energy lines. No splitting of the 0.9952 eV line is detected. The g‖-value for the 1.0015 eV and 1.0020 eV lines are g‖ = 1:4 and g‖ = 1:7, respectively. For both lines, g⊥ = 0. The C3v symmetry indicates that the UD-1 center is either a substitutional defect or a complex with its constituents lying along the c-axis of the lattice.

Epitaxial growth on Si-face nominally on-axis 4H-SiC substrates has been performed using horizontal Hot-wall chemical vapor deposition system. The formation of 3C inclusions is one of the main problem with growth on on-axis Si-face substrates. In situ surface preparation, starting growth parameters and growth temperature are found to play a vital role in the epilayer polytype stability. High quality epilayers with 100% 4H-SiC were obtained on full 2" substrates. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that the replication of the basal plane dislocation from the substrate into the epilayer can be eliminated through growth on on-axis substrates. Also, no other kind of structural defects were found in the grown epilayers. These layers have also been processed for simple PiN structures to observe any bipolar degradation. More than 70% of the diodes showed no forward voltage drift during 30 min operation at 100 A/cm(2).

Electron paramagnetic resonance (EPR) studies of the P6/P7 centers in 4H- and 6H-SiC are reported. The obtained principal values of the hyperfine tensors of C and Si neighbors are in good agreement with the values of the neutral divacancy (VCVSi 0) calculated by ab initio supercell calculations. The results suggest that the P6/P7 centers, which were previously assigned to the photo-excited triplet states of the carbon vacancy-carbon antisite pairs in the double positive charge state (VCCSi 2+), are related to the triplet ground states of the C3v/C1h configurations of VCVSi 0.

Intrinsic defects are of importance for different applications of SiC such as: the semi-insulating (SI) properties of SI substrates, the carrier lifetime of high-voltage, bipolar power devices and the colour of gemstones (Moissanites). In order to tailor the properties of the material, we need to understand the properties of the intrinsic defects, their energy positions in the bandgap, their ability to capture carriers from the bands, their formation and annealing as well as their interplay with other defects. High-purity SiC materials (doping less than 10(16) cm(-3)) grown by high temperature chemical vapour deposition (HTCVD), physical vapour transport (PVT) and chemical vapour deposition (CVD) have been investigated by electron paramagnetic resonance (EPR), photoluminescence (PL), absorption and electrical techniques. Vacancies (V-C(+), V-Si(0)), divacancies and anti site-related defects are found to be common. The present knowledge of intrinsic defects in SiC based on both experiments and on calculations will be presented as well as their influence on mainly the semi-insulating properties. (c) 2005 Elsevier B.V. All rights reserved.

The P6/P7 centers in 4H-SiC were studied by electron paramagnetic resonance (EPR) and ab initio supercell calculations. The hyperfine coupling constants of C and Si neighbors obtained by EPR are in good agreement with the calculated values for the neutral divacancy, VCVSi0. Our results suggest that the P6/P7 centers, which were previously assigned to the photo-excited triplet states of the carbon vacancy–carbon antisite pairs in the double positive charge state (VCCSi2+), are related to the triplet ground states of the C3v/C1h configurations of VCVSi0.

Defects and impurities in high-purity semi-insulating (HPSI) SiC substrates grown by high temperature chemical vapour deposition (HTCVD) and physical vapour transport (PVT) are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The carbon vacancy in the positive charge state (V-C(+)) is observed in all HTCVD, and PVT HPSI substrates. EPR signals of (C-Si-V-C) pairs are often detected in HPSI samples. The T-V2a, which was previously attributed to V-Si(0), is often observed with different concentrations in HTCVD material. The (+/0) donor level of V-C at 1.47 eV above the valence band is suggested to be important for the Slproperties of HPSI 4H-SiC substrates with the activation energies E(a)similar to1.4-1.5 eV. The SI-5 center may be related to the vacancy pair in the negative charge state (V-C-V-Si)(-) and its acceptor level (-1/-2) is in the region similar to1.24-1.51 eV below the conduction band. This center is stable at annealing temperature of 1600 degreesC. After annealing, V-C(+) and V-Si-related signals decrease but can still be observed, whereas the (C-Si-V-C) pairs completely disappear.

Advances in the development of the HTCVD technique for growth of bulk 2-inch diameter 4H SiC crystals are reviewed with demonstration of micropipe density down to 0.3 cm(-2), low crystal bending and X-ray rocking curve widths of 12". High Al doping in p-type substrates enables resistivities down to 0.5 Omega cm without increased micropipe density, while too high N doping causes spontaneous stacking faults formation in annealed n-type substrates. High purity semi-insulating wafers, grown under conditions reducing the incorporation of Si-vacancies, exhibit lower density of vacancy clusters and better properties for microwave device applications.

DC and RF measurements for MESFET devices fabricated on three different 4H-SiC Semi-Insulating (SI) substrates are compared in this paper and the epilayers were grown simultaneously for all three wafers. The different wafers were processed during the same batch run. The MESFETs processed on the high-purity wafers showed less light sensitivity than those processed on the Vanadium doped wafer.

By using the HTCVD technique together with Al doping, highly p-type doped 2" diameter 4H-SiC off-axis substrates with micropipe densities below 10 cm(-2) were grown. The Al concentration in the substrates could be varied from low 10(15) cm(-3) to low 10(19) cm(-3). Bulk resistivities down to 0.5 Omega-cm were realized. There were no indications of micropipe formation from Al precipitates, on the contrary, micropipe closing was observed.

Semi-insulating silicon carbide single crystals have been grown using high temperature chemical vapor deposition without vanadium doping. The resistivity of standard and exploratory 2″ diameter substrates has been analysed topographically with 1 mm lateral resolution with an improved contactless resistivity mapping technique. Absolute resistivity values are ranging from below 1 × 105 to above 1 × 1012 Ω cm. The lateral homogeneity of state-of-the-art material is very satisfactory, whereas strong localized inhomogeneities in exploratory materials underscore the decisive advantage of a nondestructive and topographic resistivity evaluation in supporting the optimization of the crystal growth procedure.