Ion Bombarment Effect on the Growth of Microcrystalline Germanium

Abstract

AbstractThe influence of surface mobility on the growth of Ge films is studied as a function of preparation conditions. The positive ion bombardment during film deposition on chromium substrates is analyzed using an electrostatic analyzer. The dielectric functions of the films are measured over the range 1.7–4.5 eV using in-situ spectroscopic phase modulated ellipsometry (SPME). The spectra of microcrystalline germanium (μc-Ge) present a shoulder near 4.2 eV which corresponds to the E2. optical transition observed in single crystal germanium. For substrate temperatures greater than 150°C, a transition from a-Ge:H to μc-Ge appears when the ion kinetic energy exceeds a threshold energy Eth, around 120 eV. Eth decreases as a function of substrate temperature. The Eth value is found to be higher than the threshold value corresponding to the opposite transition, giving evidence of a substrate memory effect on the growth of μc-Ge. Kinetic ellipsometry measurements of the early stage of the μc-Ge deposition on chromium are accurately, modelled by microcrystalline nucleation at a 50 Å level. After 200 Å thickness, μc-Ge grows with an overlayer. The description of μc-Ge as a mixture of c-Ge, a-Ge:H and voids is discussed.