Postannealing effects on undoped BaSi2 evaporated films grown on Si substrates

Semiconducting BaSi2 is expected as an alternative material for solar cell application because of large absorption coefficients and a suitable bandgap for single-junction solar cells. In this study, the electrical properties of undoped BaSi2 films grown by a simple vacuum evaporation method are explored. The obtained results show that an undoped evaporated film is an n-type semiconductor with a high carrier density of similar to 10(19) cm(-3) and exhibits a metallic behavior. The quality of BaSi2 films is significantly improved by postannealing at 1000 degrees C with surface covering to prevent oxidation. After annealing, the carrier density of BaSi2 films markedly decreases and the temperature dependence of carrier density changes from being metallic to being semiconducting. By comprehensive structural analysis, it is speculated that postannealing improves the film quality, for example, by decreasing the density of grain boundaries. (C) 2017 The Japan Society of Applied Physics