Electrical Measurement of the Vanadium Acceptor Level in 4H- and 6H-SiC

Abstract

AbstractTemperature dependent Hall effect, Fourier transform infrared absorption, and electron paramagnetic resonance (EPR) studies have been performed on both 6H and 4H vanadium doped semi-insulating SiC samples grown by the physical vapor transport technique. Nitrogen and boron concentrations have been measured in some samples by secondary ion mass spectrometry (SIMS). Unlike undoped s.i. SiC, where several different thermal ionization energies have been observed, the ionization energies for all of the vanadium doped s.i. samples studied here were found to cluster around only two values for the two polytypes, EC – 0.85 eV and EC – 1.54 eV for 6H and EC – 1.11 eV and EC – 1.57 eV for 4H. SIMS measurements indicate that the nitrogen concentration exceeds the boron concentration in samples with the shallower of two values while the opposite is true for the deeper level samples. EPR detected both V3+ and V4+ in shallower level samples while only V4+ was detected in the deeper level samples. These results indicate that the vanadium acceptor level, V3+/4+, is located at EC – 0.85 eV in 6H-SiC and EC – 1.11 eV in 4H-SiC. However, some EPR results do show a small, unexpected asymmetry in the angular dependence of the V4+ signal, most noticeably in the 4H samples. This suggests that at least some of the vanadium related levels might be complexed with another defect or be under higher local strain than expected.