6H-SiC single crystals doped with aluminum acceptors at different concentrations were investigated with admittance spectroscopy and Hall effect. Thermally activated impurity conduction was observed at temperatures below 160K. The activation energy of 17meV was obtained from admittance spectroscopy as well as from temperature-dependent resistivity measurements. The Hall coefficient showed a sign reversal in the temperature range where hopping conduction dominates.
Three topics are reported in this paper: (a) the determination of a temperature-dependent Hall scattering factor for holes r H,h (T) in 4H-SiC, (b) the detection of shallow Al-related defect centers in Al-doped, p-type 6H-/3C-SiC; these defects are generated either by implantation of any ion species or by an oxidation process and (c) the observation of absorption lines in infrared (IR) spectra, which are due to phosphorus donors in 6H-SiC.
A brief survey of the development of the sublimation growth of SiC is given. The growth equipment and especially the hot zone of the furnace for the physical vapour transport (PVT) technique are described in detail. In order to grow micropipe-free SiC crystals, near-thermal-equilibrium growth is developed and the individual processing steps are revealed. The essential parameters for the growth of 4H-, 6H-, 15R-and 3C-SiC single crystals are discussed and a survey of the incorporation of donors (N, P) and acceptors (Al, B) during the PVT growth is presented.
We report on admittance spectroscopy (AS) investigations taken on aluminum (Al)-
doped 6H-SiC crystals at low temperatures. Admittance spectra taken on Schottky contacts of
highly doped samples (NA ≥ 7.2×1017 cm-3) reveal two series of conductance peaks, which cause
two different slopes of the Arrhenius plot. The steep slope is attributed to the Al acceptor, while the
flatter one - obtained from the low temperature peaks - is attributed to the activation energy ε3 of
nearest neighbor hopping. We propose a model, which explains the unexpected sharpness of the
low temperature conductance peaks and the disappearance of these peaks for low acceptor
concentrations. The model is verified by simulation, and the AS results are compared with
corresponding results obtained from resistivity measurements taken on 4H- and the identical 6HSiC
samples.
In this paper, we study the polytype transformation of cubic silicon carbide (3C-SiC) by micro Raman spectroscopy. Two sets of samples are investigated. First, physical vapor transport (PVT) grown samples, grown on chemical vapor deposition (CVD) substrates at growth temperatures between 1800 and 1950°C. The microscopic images of the cross sections and the Raman spectra taken on these grown crystals show a growing fraction of 6H-SiC inclusions with increasing growth temperature. To decide whether these polytype inclusions are induced by the PVT growth process or by the temperature treatment of the CVD substrates, we studied the temperature induced polytype coversion of cubic CVD substrates grown on undulant Si(100) surfaces which were used as seed crystals for the PVT growth. The CVD substrates were annealed in the temperature range between 1700 and 2100°C. The results of this annealing series are similar to the results we find in the PVT grown samples. Therefore we argue that the polytype conversion is not induced by the PVT growth process but a result of the heat treatment of the CVD seed crystals.
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