Zhang Peng-xiang

Giant Temperature Coefficient of Resistance in ZnO/Si (111) Thin Films

Giant negative temperature coefficient of resistance (TCR) was observed in ZnO/Si (111) thin films. The films were grown using the pulsed laser deposition (PLD) technique, taking Si (111) wafer as substrates, with a substrate at the temperature below 450°C in the PLD. It is found that both TCP-temperature behavior and TCP, value are strongly affected by deposition temperature. The maximal TCP, value over −10.9%K−1 can be observed at the deposition temperature from 20°C to 350°C and reaches to −13%K−1 at deposition temperature 20°C where the film shows X-ray diffraction amorphous. The results suggest that the ZnO/Si films demonstrate great potentials when used in a low-cost, high-performance, non-cooling and highly sensitive bolometer.

Thermoelectric signals from Si/SiGe superlattices

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.

The transverse laser induced thermoelectric voltages in step flow growth (1 ? x)Pb(Mg1/3Nb2/3)O3?xPbTiO3 thin films

This paper reports that the transverse laser induced thermoelectric voltages (LITV) are observed for the first time in the step flow growth (1 — x)Pb(Mg1/3Nb2/3)O3—xPbTiO3 (PMN-PT, x = 0.20, 0.33, 0.50) thin films deposited on vicinal-cut strontium titanate single crystal substrates. Because lead magnesium niobate-lead titanate is a solid solution of lead magnesium niobate (PMN) and lead titanate (PT), there are two types of signals. One is wide with a time response of a microsecond, and the other superimposed with the wide signal is narrow with a time response of a nanosecond. The transverse LITV signals depend on the ratio of PMN to PT drastically. Under the irradiation of 28-ns pulsed KrF excimer laser with the 248-nm wavelength, the largest induced voltage is observed in the 0.50Pb(Mg1/3Nb2/3)O3—0.50 PbTiO3 films. Moreover, the effects of film thickness, substrates, and tilt angles of substrates are also investigated.