Papers by Keyword: Band-Tail States

Abstract: Quaternary AlInGaN/AlInGaN multiquantum-well (MQW) structures were grown by metal-organic vapour-phase epitaxy (MOVPE). The influence of QW pairs and QW barrier width on the optical properties of the samples is investigated by means of temperature and incident-power dependent photoluminescence (PL) measurements. The PL emission peaks redshift and the PL peak intensities increase as the number of QW pairs increases. On the other side, a blueshift of the PL peak energy and reduction of the PL peak intensity are observed for the sample with thinner barrier width. These results are explained by carrier localization effect. The S-shaped temperature-dependence of the PL peak energies indicates the existence of localized states induced by the potential fluctuations. The estimated degree of localization effect is found to be enhanced for the sample with more QW pairs and thicker barrier layers. Observing the incident-power dependent PL spectra, the estimated amounts of localization effect of the samples are consistent with the incident-power induced blueshifts of PL peak energies and the slope exponents of power-law form of integrated PL intensity.

Abstract: Hall measurements on NO annealed 4H-SiC MOS gated Hall bars are reported in the temperature range 77 K- 423 K. The results indicate higher carrier concentration and lower trapping at increased temperatures, with a clear strong inversion regime at all temperatures. In stark contrast to Si, the Hall mobility increases with temperature for 77 K-373K, above which the mobility decreases slightly. The maximum experimental mobility was found to be ~50 cm² V^-1 s^-1 which is only about 10% of the 4H-SiC bulk mobility indicating that while NO annealing drastically improves trapping, it does not improve the mobility significantly. Supporting modeling results strongly suggest the presence of a disordered SiC channel region.