Thermoelectric signals from Si/SiGe superlattices

Abstract

p-Si/Si0.5Ge0.5 superlattices (SLs) grown on a vicinal-cut p-type silicon single crystalline substrate by molecular beam epitaxy (MBE) were irradiated by a KrF excimer laser. Two types of transient laser induced voltage (LIV) signals were observed, among which the signals of 0.3 V in amplitude with time response ∼40 ns showed up along the tilted directions, while voltage signals of ∼10 mV with a time response of tens of microseconds presented along the untilted directions which were perpendicular to the tilted direction. The results demonstrate that the observed photoelectric signals of 0.3V amplitude are laser induced thermoelectric voltages (LITV) due to the tilting angle relation. The observed LIV signals implied that these SLs exhibited anisotropic Seebeck components. It was also found that the LIV signals increased with the p-type doping level in the Si layer, which was coincident with the expectation of the laser induced thermoelectric effect. According to the measured signals and the theoretical formula, one can calculate the physical parameters of the SLs. The calculated effective Seebeck anisotropy coefficients (Sab − Sc) for samples with 1018 cm−3 and 1020 cm−3 are approximately 11.2 µV K−1 and 18.2 µV K−1, respectively.