Effect of doping on properties of hexagonal polytype silicon carbide crystals

The purpose of this study is to understand the effect of the incorporation and presence of nitrogen on the properties of SiC crystals.; Using the Halide Chemical Vapor Deposition system, high-purity SiC crystals were grown to study the incorporation behavior of dopant (especially N and B). Doping concentration was measured by the capacitance-voltage method, Hall measurements and secondary ion mass spectrometry. It was shown that, with the increase of the C/Si ratio, N incorporation decreased, B incorporation increased, and as a result, the resistivity of samples increased. At very low C/Si ratio, samples were n-type and the increase of resistivity is due to the decreasing concentration of uncompensated N and the increased role of the additional 0.27 eV donor located deeper than usual N donor levels. Increase of the C/Si ratio above 0.36 resulted in the p-type material. The relatively high resistivity of the compensated p-type samples is due to the low concentration of uncompensated B and a considerable depth of the 0.3 eV B acceptors. The highest C/Si ratio growth produced very high-resistivity p-type samples with an activation energy of 0.6 eV This energy level appears to be the B-related deep centers which are known to be complexes of B atoms and intrinsic defects.; Lattice parameter and optical absorption spectra were measured on heavily nitrogen-doped bulk crystals and epilayers of 4H-SiC. The rate of c-lattice parameter change versus doping concentration in high quality material was less than -3.6 x 10-25 Acm3 . In crystals containing high density of nitrogen-induced double stacking faults, the (0008) x-ray reflection shifted toward the (222) reflection in 3C-SiC. Optical absorption spectra of faulted 4H material show an additional peak located at 3.1 eV similar to that reported in nitrogen doped 3C bulk crystals. Comparison of the free carrier absorption intensities in as-grown and annealed samples indicates the transfer of electrons from the 4H matrix to the stacking fault-induced quantum wells.; Stacking fault formation in n+ 4H-SiC epilayers (n = 9 x 1019 cm-3) deposited on the 4H-SiC substrates (n = 5 x 1018 cm-3) has been observed by conventional and high-resolution transmission electron microscopy (HRTEM). Formation of faults occurred during annealing in Ar at 1150°C for 90 min. All faults were identical double layer Shockley faults formed by the glide of partial dislocations on two neighboring basal planes. The sign of the Burgers vector for several of the partial dislocations bounding the faults at the epilayer/substrate interface has been determined by HRTEM. Approximately half the dislocations had a sign corresponding to the extra half-plane inserted into the epilayer, while the other half resulted in the removal of the same half-plane from the film. In one case, two faults bounded by opposite sign dislocations were separated by only 80 nm. This result is inconsistent with mechanical stress due to the doping difference between the epilayer and the substrate as a driving force of fault expansion. Formation of single Shockley stacking faults was also observed in n+ 6H-SiC epilayers.