Low field electron mobility in heavily nitrogen doped 4H-SiC epitaxial layers as well as in the regions formed by ion implantation was extracted from Hall and van der Pauw measurements. The measurements were done at room temperature in 4H-SiC samples with carrier concentrations ranged from 2.8×1018 to 2.3×1019 cm-3. Fitting parameters in empirical expression given by Caughey and Thomas for room temperature low field electron mobility depending on carrier concentration in 4H-SiC were extracted.
Density functional calculations were performed for the –H, –OH and –F functional groups adsorbed onto the surface of pseudo-spherical 4H-SiC quantum dots with diameters ranging from 10 to 22 Å. We find that for the investigated diameter range, the H-terminated SiC-quantum dots exhibit strong size dependent quantum confinement effects, while for –F and –OH terminations, the optical gap remains largely unchanged. The –H termination shows an optical absorption onset well above that of –F and –OH for a similar cluster size, which is attributed to the localisation of HOMO and LUMO states to the quantum dot core. Based on our calculations, we suggest that the –H functionalisation is a more promising route for engineering the optical properties of SiC-quantum dots, since this could lead to a wider control over the optical absorption onsets, when compared to –OH and –F terminations.
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