Intrinsic deep levels in semi-insulating silicon carbide

High temperature Hall effect and resistivity measurements have been made on undoped, high purity semi-insulating (HPSI) 4H SiC samples. Both physical vap*or transport and high temperature chemical vapor deposition grown samples have been investigated. Resistivity measurements before and after annealing at temperatures up to 1800degreesC are also reported. Hall and resistivity results are compared with low temperature photoluminescence results. The thermal activation energies for HPSI material taken from temperature dependent resistivity measurements varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI. In all cases the material was found to be ntype and the measured carrier concentration activation energies agreed within a few tens of percent with the resistivity activation energies. Mixed conduction analysis of the data suggests that the hole concentration was negligible in all of the samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap.