Anisotropy of mobility ratio between electron and hole along different orientations inReGexSi1.75−xthermoelectric single crystals

It was recently found that $\mathrm{Re}{\mathrm{Si}}_{1.75}$ based semiconductor single crystals can be of either $p$ or $n$ type with a fixed composition, just depending on their different crystal orientations. To investigate the mechanism of this interesting phenomenon, we grow $\mathrm{Re}{\mathrm{Ge}}_x{\mathrm{Si}}_{1.75-x}$ ($x=0.02$ and 0.04) single crystals with a floating zone method with radiation heating. The Seebeck coefficient and electric resistivity of these samples are measured along [100] and [001], respectively. The conduction mechanism is of $p$ type along [100] and of $n$ type along [001], like binary $\mathrm{Re}{\mathrm{Si}}_{1.75}$, in the temperature range $50\text{to}800°\mathrm{C}$. The mobility ratio between electron and hole is calculated from the Seebeck coefficient data and it is highly anisotropic along two different orientations (about 0.4 to 0.6 along [100] while 4 to 5 along [001] direction), giving rise to the orientation-dependent conduction sign reversal phenomenon observed in $\mathrm{Re}{\mathrm{Si}}_{1.75}$.