Papers by Author: Roland Weingärtner

Abstract: Amorphous pseudobinary (SiC)1 x(AlN)x thin films have been produced by radio frequency dual magnetron sputtering from bulk SiC and AlN targets. For each target the emission characteristic, i.e. the spatial variation of the deposition rate was determined, in order to predict thickness distribution and spatial composition variation for the (SiC) (AlN) alloy. Impedance spectroscopy shows a high resistivity of the films in the SiC rich region, decreasing significantly towards the AlN rich region.

Abstract: Amorphous wide bandgap semiconductor thin films of the pseudobinary compound (SiC)1-x(AlN)x were grown by radio frequency dual magnetron sputtering on CaF2, MgO and glass substrates. We performed isochronical annealing steps up to 500°C. The optical bandgap is determined for each composition from spectroscopic transmission measurement in two different ways: according to Tauc and using the (αhν)2 plot. The dependence of the optical bandgap on the composition x can be described by Vegard’s empirical law for alloys.

Abstract: We produce amorphous terbium doped wide bandgap semiconductor thin films of the pseudobinary compound (SiC)1 x(AlN)x by rf triple magnetron sputtering. Cathodoluminescence measurements performed at samples having different compositions x show pronounced intra 4f shell transition peaks of the trivalent terbium. Thermal activation of the terbium emission by isochronal annealing of the films leads to a strong increase in emission intensity.

Abstract: We present comprehensive cathodoluminescence measurements from thin amorphous a- SiC films doped with rare earths. The a-SiC films were prepared by rf magnetron sputtering using a high purity SiC wafer in high purity argon atmosphere (5N, pressure approx. 0.2 mbar). The rare earth doping (Tb, Dy and Eu concentrations were below 2%) was performed by placing respective rare earth metal pieces of appropriate size onto the Silicon Carbide wafer. The rare earth ion emissions cover the colors green (Tb), yellow (Dy) and red (Eu). The optical and related structural properties of the films are correlated by means of high resolution transmission electron microscopy in combination with cathodoluminescence measurements in a scanning electron microscope. In addition, the corresponding compositions are determined by energy-dispersive x-ray analysis. The cathodoluminescence spectra of the rare earth 3+ ions are recorded in the visible at 20°C in the asgrown condition and after annealing treatments in the temperature range from 300°C to 1050°C by steps of 150°C. The anneal-related changes in the cathodoluminescence emission spectra and in the microstructure of the films are addressed. The SiC films show amorphous structure almost independent of the annealing treatment. Optimal annealing temperature for emissions of Tb3+ doped a-SiC were derived to be 600°C whereas Dy3+ and Eu3+ emissions increase at least up to 1050°C.

Abstract: Several highly aluminum doped SiC bulk crystals were grown with a modified PVT (MPVT) method. To facilitate 4H-SiC formation, growth was conducted on the C-face. The samples were investigated using Hall measurements in the Van-der-Pauw geometry. Lowest room temperature values for specific resistivities were 0.09 Ωcm for 6H-SiC and 0.2 Ωcm for 4H-SiC, which are to our knowledge the lowest values yet reported in literature. Thus, resistivity values of < 0.2 Ωcm, which are required for substrates in high power device applications, could be demonstrated for 4HSiC. Remarkably, in very highly doped samples the type of conduction could not be determined by Hall measurements.