A novel heteroepitaxy method of Ge films on CaF2 by electron beam exposure

A novel heteroepitaxy method of Ge films on CaF2/Si(111) structures is presented, in which two successive processes of electron beam (e-beam) exposure and predeposition of thin Ge layers at room temperature are done prior to the growth of thick Ge films at elevated temperatures. It was found in the e-beam exposed region that the island growth of the predeposited Ge layer was prevented and the surface morphology and crystalline quality of the Ge overlayer grown at 600 °C were dramatically improved. These results were virtually independent of the sequence of the predeposition and exposure processes. From discussion on the growth mechanism of this method, a most plausible model that e-beam dissociates the surface composition of CaF2 and improves the wettability between Ge and CaF2 is proposed.