Electrical properties of unintentionally doped semi-insulating and conducting 6H-SiC

Abstract

Temperature dependent Hall effect ͑TDH͒, low temperature photoluminescence ͑LTPL͒, secondary ion mass spectrometry ͑SIMS͒, optical admittance spectroscopy ͑OAS͒, and thermally stimulated current ͑TSC͒ measurements have been made on 6H-SiC grown by the physical vapor transport technique without intentional doping. n-and p-type as well semi-insulating samples were studied to explore the compensation mechanism in semi-insulating high purity SiC. Nitrogen and boron were found from TDH and SIMS measurements to be the dominant impurities that must be compensated to produce semi-insulating properties. The electrical activation energy of the semi-insulating sample determined from the dependence of the resistivity was 1.0 eV. LTPL lines near 1.00 and 1.34 eV, identified with the defects designated as UD-1 and UD-3, were observed in all three samples but the intensity of the UD-1 line was almost a factor of 10 more in the n-type sample than in the the p-type sample with that in the semi-insulating sample being intermediate between those two. OAS and TSC experiments confirmed the high purity of this material. The results suggest that the relative concentrations of a dominant deep level and nitrogen and boron impurities can explain the electrical properties in this material.

Compensating defect centres in semi-insulating 6H-SiC

“…The centres TU4 (80 meV), TU5 (110 meV) and TU7 (125 meV) can be identified with the shallow nitrogen donors located in the h, k 1 , and k 2 lattice sites, respectively. The activation energies of these centres are in very good agreement with the ionization energies of the particular ni− trogen donors [4,6,8]. In view of the results reported in Refs.…”

“…The former trap has been attributed to a carbon vacancy and the latter has been as− signed to a complex involving a silicon antisite [20,21] ture photoluminescence spectra [3,4]. However, the micro− scopic structure of this defect still remains unknown.…”

“…10 and 12, the centre TV9 (870 meV) seems to be related to a silicon vacancy. The centres TV10 (1200 meV), TV11 (1370 meV), and TV12 (1380 meV), are also likely to be attributed to native defects or complexes involving a na− tive defect and a residual impurity [3,4,11,17] reported in Refs. 3, 4, and 17, confirm the presence of these centres in SI SiC by photoluminescence (PL) and thermally stimulated luminescence measurements.…”

“…It is worth noting, that the photocurrent relaxation waveforms were very complex in this temperature range and consisted of the signals either with the positive or negative amplitude. The relaxations with the negative amplitude are most likely to be due to the thermal emission of electrons from the shal− low donors that at low temperatures are partly ionized and responsible for the material compensation [1,4,8]. On the grounds of the experimental data received so far [5,18], the centres TU1 (50 meV) and TU2 (60 meV) can be assigned to shallow phosphorus donors in different lattice sites (h and k 1 or k 2 ).…”

“…The SI SiC crystals are mainly grown by physical vapour transport (PVT) tech− nique and a high resistivity, ranging from 10 7 -10 11 Ùcm, is obtained by doping with vanadium (3d 3 4s 2 ) that is an am− photeric impurity in SiC acting as a deep acceptor as well as a deep donor compensating shallow level impurities such as residual nitrogen and boron [1]. At present, however, the semi−insulating properties of SiC crystals can also be achieved without vanadium doping, by maintaining the high material purity and introducing deep intrinsic point defects that compensate the residual shallow impurities [2][3][4].…”