Effects of molecular beam epitaxy growth conditions on grain size and lattice strain in a-axis-oriented BaSi2 films

We grow 0.5 μm thick a-axis oriented BaSi2 films on Si(111) substrates by a conventional two-step growth method and compare their properties with those grown by a three-step growth method. Both grow methods consist of the initial growth of a BaSi2 template layer and the following molecular beam epitaxy (MBE) to form BaSi2 films. In the two-step growth method, Ba-to-Si deposition rate ratios (RBa/RSi) were varied in the range 0.4–4.7 during MBE. On the other hand, in the three-step growth method, MBE-grown BaSi2 layers are composed of BaSi2 films grown first under Ba-rich conditions (RBa/RSi = 4.0), followed by those grown under Si-rich conditions (RBa/RSi = 1.2). The grain size of BaSi2 films by the three-step growth method was much smaller than those grown by the two-step growth method. To our surprise, however, much higher photoresponsivity was obtained for BaSi2 films grown by the three-step growth method.