For fabricating photovoltaic BaSi2 films with controlled carrier density and suppressed oxidation by thermal evaporation, the mechanism determining the film composition from incongruently evaporated BaSi2 must be elucidated. We investigated the effects of source premelting, substrate temperature, and thickness on the structural and electrical properties of evaporated BaSi2 films. It is found by room-temperature deposition that the vapor composition continuously changes from being Ba-rich to being Si-rich. Source premelting suppresses the deposition of Ba-rich vapor. Deposition at 600–700 °C shows that BaSi2 forms through the mutual diffusion of Ba and Si, followed by surface oxidation by residual gas. Surface oxidation can be suppressed by a-axis-oriented growth. By changing the film thickness, the optimum thickness to obtain homogeneous films with suppressed oxidation is revealed. Sufficient diffusion leads to high film resistivities and low electron densities, which demonstrates a close relationship between the film composition and the electrical properties.

Thermal evaporation is a simple method to fabricate a BaSi2 film, a new solar cell material consisting of earth-abundant elements. In this study, we optimized the evaporation process and suppressed near-interface oxidation in evaporated BaSi2 films on Si(100) substrates, which has been detected in previous studies. Composition depth profiles determined by Auger electron spectroscopy show the decrease of oxygen concentration near the interface to the background level by optimizing the source pre-melting condition. By reducing oxygen concentration, the BaSi2 film becomes more preferentially oriented toward [100] as long as the deposition rate is not changed, as evidenced by X-ray diffraction. It is also shown that the rectification behavior of n-BaSi2/p+-Si diodes improves by suppressing the near-interface oxidation.

Transport properties of polycrystalline Si1−xGex (x = 0, 30, 50 and 70) thin films on SiO2 were studied by Hall measurements and transport properties of the TFTs fabricated on the films were characterized. Si1−xGex films were p-type in spite of non-doping. Room temperature hole densities of Si1−xGex films increased from 5 × 1013 to 5 × 1016 cm−3 as Ge concentration increased from 30 % to 70 %. The acceptor levels in Si1−xGex were located at 0.43, 0.40 and 0.34 eV for x=0.3, 0.5 and 0.7 from valence band, respectively. The high leakage current of SiGe-TFTs was observed and drain current could not be turned off even when the high gate voltage was applied. The acceptor density increased with increasing annealing temperature from 700 °C to 800 °C. The leakage currents were independent of the annealing temperature and is thought to originate from Ge-related defects in grain boundaries.