Vanadium (V) doped SI SiC has been developed since the 1990s. However, SiC MESFETs using V-doped SI SiC substrates are shown to have severe problems with electron trapping to eep levels in the SI substrates which causes reduction of the drain current and instability of the device performance. Since the beginning of this decade, V-free high-purity SI (HPSI) SiC substrates using intrinsic defects to compensate the N donors have been developed. The work in this thesis has been devoted to characterize defects in HPSI SiC using electron paramagnetic resonance (EPR). EPR detects transitions between energy levels split up by the interaction of unpaired electron spins (localized at the defect and neighboring atoms) with an applied magnetic field. Thanks to the sensitivity of the electron spins to their surroundings; especially to nearby nuclear spins that further splits the energy levels by the so-called hyperfine (hf) interaction, one can extract information on the structure and electronic configuration of a defect.
The work has been focused on (i) the identification of prominent defects, (ii) the determination of their energy levels and roles in the carrier compensation processes, (iii) the defect interaction and the stability of the SI properties at high temperatures, in order to identify the optimal defect(s) to be used for controlling the SI properties. EPR and ab initio supercell calculations have been the main tools for defect identification and all three common polytypes 3C-, 4H- and 6H-SiC of different conducting types (n-, p-type and SI) have been investigated. For determination of the energy levels in the bandgap, the combined results of EPR and photoexcitation EPR (photo-EPR), Deep Level Transient Spectroscopy (DLTS), the temperature dependence of the resistivity, and ab initio calculations have been evaluated. Annealing studies up to 1600 °C for samples with different defect compositions have been carried out for obtaining knowledge on the defect interaction and thermal stability of the SI properties as well as the change in resistivity, activation energy and defect concentration. Below is a short summary of the papers included in the thesis.
(Text from Ph.D. Dissertation Patrik Carlsson)
Responsible for this page: Fredrik Karlsson
Last updated: 04/18/11