Vanadium donor and acceptor levels in semi-insulating 4H- and 6H-SiC

Abstract

The electronic levels of vanadium in semi-insulating 4H- and 6H-SiC have been reinvestigated using temperature dependent Hall effect and resistivity measurements at temperatures up to 1000K in conjunction with electron paramagnetic resonance (EPR) and optical absorption measurements which were used to identify the charge state of vanadium in the material. Two distinct thermal activation energies were found for each polytype. The shallower of the two levels correlated with the presence of both V3+ and V4+ in the EPR and absorption experiments, demonstrating that this level is the vanadium acceptor level while the deeper level is the donor level for which the V4+ charge state was observed. The results for the V4+∕5+ donor level, EC−1.57±0.09eV for 4H-SiC and EC−1.54±0.06eV for 6H-SiC, are in agreement with the generally accepted values. However, the results for the V3+∕4+ acceptor level, EC−0.85±0.03eV in 6H-SiC and EC−1.11±0.08eV in 4H-SiC, are significantly higher than previously assumed. Variations in crystal quality and purity may explain the differences in the previously reported values for the donor and acceptor levels.

Compensating defect centres in semi-insulating 6H-SiC

“…3, 4, and 17, confirm the presence of these centres in SI SiC by photoluminescence (PL) and thermally stimulated luminescence measurements. The centres TV13 (1520 meV) and TV 14 (1630 meV) can be assigned to the vanadium donor V 5+/4+ [9,16]. The experimental data obtained recently indicate [9,16] that the former is presumably related to the va− nadium donor at the hexagonal site and the latter can be assigned to the vanadium donor at the quasi−cubic lattice site k 1 or k 2 .…”

“…On the other hand, the centre TV8 (835 meV) can be identified with the vanadium acceptor V 3+/4+ at the hexago− nal lattice site [9,16]. In view of the results reported in Refs.…”

“…The former can be attributed to the boron acceptor at the quasi−cubic k 2 site [6][7][8] or to an electron trap E2 (0.41 eV) related to a native defect [10]. The latter seems to be the va− nadium acceptor V 3+/4+ at one of the quasi−cubic sites k 1 or k 2 [9,16]. In the temperature range of 320-720 K [ Fig.…”

“…According to the results presented in Table 1, the main de− fect levels detected in SI 6H−SiC are related to boron and vanadium impurities. The atoms of these impurities can be located at various sites of the crystal lattice, and we have , vanadium donor at (k 1 , k 2 ) site [9,16] Note: n.a. stands for negative amplitude of the photocurrent relaxation waveforms.…”

“…10 and 11, the shallow centres TU3 (70 meV) and TU6 (120 meV) are of unknown origin. The centre T8 (140 meV) is presumably related to the presence of titanium, that apart from nitrogen, boron, aluminium and vanadium, is a common residual impurity in 6H−SiC [1,10,16].…”