Compensation mechanism in high purity semi-insulating 4H-SiC

A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect (TDH), thermal and optical admittance spectroscopies, and secondary ion mass spectrometry (SIMS). Thermal activation energies from TDH varied from a low of 0.55 eV to a high of 1.65 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to different charge balance equations and comparison of the fitting results with SIMS measurements indicated that the deep levels are acceptorlike even though they are in the upper half of the band gap. Carrier concentration measurements indicated that the deep levels are present in concentrations in the low 10(15) cm(-3) range, while SIMS results demonstrate nitrogen and boron concentrations in the low to mid-10(15)-cm(-3) range. The results suggest that compensation in this material is a complex process involving multiple deep levels. (c) 2007 American Institute of Physics.