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From the viewpoint of application in power electronics, SiC possesses the greatest advantage of having SiO2 as its native oxide. Unfortunately, the usual thermal oxidation produces an unacceptably high density of interface states, with a complex energy distribution. Deep states are assumed to be caused by carbon excess at the interface, while the slow electron traps, called NIT, with especially high density near the conduction band of 4H-SiC (which would be the best polytype for power devices), are expected to originate from oxide defects near the interface. Unlike the case of the Si/SiO2 interface, simple hydrogen passivation does not help to reduce the high trap density. A possible passivation method for both deep states and NIT is post-oxidation annealing or oxidation in the presence of NO or N2O molecules. Here we present systematic and sophisticated theoretical calculations on a model of the 4H-SiC/SiO2 interface, in order to establish the main reaction routes and the most important defects that are created during dry oxidation, and may give rise to the observed interface traps. We also investigate the effect of nitrogen in suppressing them.

The small bulb of the tungsten halogen lamp often operates at several hundred degrees Celsius and an internal pressure higher than atmospheric pressure. The cold lamp contains a gas filling at about 3 bar; the pressure during operation is much higher than that. The objective of our project is to analyse the internal operating conditions (such as the pressure and the thermal behaviour) of certain halogen lamps. The actual measurement of the operating conditions is far from easy. Rather, a computer model has been developed to evaluate the operating conditions in these lamps, based on the substantial partial differential equations of the free convection problem. This model can help determine the temperature distribution, the velocity field and the pressure in these lamps.The free convection has been simulated by the following two appropriate equations: the convection–conduction equation—it is the heat transfer equation for convecting materials—and the incompressible Navier–Stokes equation. We could get the temperature field from our results, which helped us to calculate the operating pressure of the lamps. The pressure dependence on dimensionless characteristic numbers was evaluated.

La5Ti2Cu1−x Ag x S5O7, a solid solution of La5Ti2CuS5O7 and La5Ti2AgS5O7, is a semiconductor studied for sunlight-driven water splitting. In this study, the band structure and effective mass of La5Ti2Cu1−x Ag x S5O7 solid solutions are analyzed on the basis of density functional theory (DFT) calculations to reveal the effect of the composition on the band structure and the anisotropy in the conductivity. The band gap of La5Ti2Cu1−x Ag x S5O7 materials exhibits a bowing with respect to the value of x. The effective masses of holes and electrons in La5Ti2Cu1−x Ag x S5O7 are estimated from the band structure. Both holes and electrons have smaller effective masses in the b-axis direction than in the other directions, testifying the highly anisotropic electronic properties. The wave functions at the valence band maximum and the conduction band minimum are both delocalized along the b-axis only, forming parallel channels for electron and hole conduction. These results support the experimental observation that photoexcited carriers tend to migrate one dimensionally. The outcome of the theoretical calculation is qualitatively consistent with the experimental observations and helps to understand the electronic properties of La5Ti2Cu1−x Ag x S5O7 with varying compositions.