Effective Masses in SiC Determined by Cyclotron Resonance Experiments

Abstract

The current status and future perspectives of cyclotron resonance (CR) experiments in SiC are given, with a brief review of published results. CR experiments have so far been successful only in 3C, 4H and 6H SiC. Among them, 3C has the best established properties. The location of the conduction band (CB) minima in 3C SiC has been shown by far-infrared CR experiments to lie at the X-point of the Brillouin zone, without the camel's back structure. The constant-energy surfaces near the CB minima are ellipsoids, with the transverse and longitudinal effective mass values as m = (0.247 ± 0.011) m0 and m = (0.677 ± 0.015) m0. The dominant electron scattering mechanism is shown to be the acoustic-phonon scattering in a very wide temperature range up to room temperature. The electron effective mass tensor in 4H SiC has been fully resolved by the optically detected CR (ODCR) studies at 35 GHz as: m(MΓ) = (0.58 ± 0.01) m0, m(MK) = (0.31 ± 0.01) m0, and m(ML) = (0.33 ± 0.01) m0. The anisotropic electron effective tensor in 6H SiC predicted by theories has, however, not been obtained so far. The limited resolution of the ODCR experiments at 9 GHz only provides the anisotropy of the electron effective masses perpendicular and parallel to the 〈0001〉 direction: m = (0.42 ± 0.02) m0 and m = (2.0 ± 0.2) m0. Future ODCR work at higher frequencies is required to fully resolve the principal values of the mass tensor. Though the CR studies are not able to locate the exact position of the CB minima, they are at least consistent with the theoretical predictions that they lie at the M-point in 4H SiC whereas in 6H SiC they are positioned at the halfway between the M- and L-point in the Brillouin zone. In both 4H and 6H SiC much effort should be made in the future to obtain information on the band non-parabolicity, the exact location of the CB minima, and also on the dominant carrier scattering mechanism. No reliable data of hole effective masses have been obtained for any polytype.