Electrical characterization studies of p-type Ge, Ge_1-ySn _y, and Si_0.09Ge_0.882Sn_0.028 grown on n-Si substrates

The electrical properties of p-type Ge, Ge_1-ySn_y, and Si_0.09Ge_0.882Sn_0.028 samples grown on n-type Si substrates using ultra-high vacuum chemical vapor deposition have been investigated as a function of temperature. Degenerate parallel conducting layers were found in all Ge/Si, Ge_1-ySn_y/Si, and Si _0.09Ge_0.882Sn_0.028/Si samples, which are believed to be associated with dislocation defects at the interface produced by the lattice mismatch between the two materials. These degenerate conducting layers affect the electrical properties of all the thin epitaxial films. Additionally, temperature dependent Hall-effect measurements show that these materials exhibit a conductivity type change from p to n at around 370-435 K. The mobilities of these samples are generally lower than that of bulk Ge due to carrier scattering near the interface between the epitaxial layer and the Si substrate and also due to alloy scattering. Detailed behavior of temperature-dependent conductivity of these samples is also discussed.