Ionized cluster beam deposition of GaAs thin films for solar cells

Abstract

Polycrystalline GaAs films have been deposited by means of an ion-assisted deposition process at a technical vacuum of 10/sup -7/ torr at the lowest possible substrate temperatures. Epitaxial GaAs layers have been produced by use of a commercial ionized-cluster-beam evaporation source as well as a modified electron-beam evaporator. Promising results concerning the electronic properties have been obtained. Net doping is on the order of 10/sup 13//cm/sup 3/, and mobility-values correspond to literature values at room temperature. The films are natively p-doped. N-doping by coevaporation of Sn has been achieved. At substrate temperatures as low as 300 degrees C, monocrystalline growth of GaAs layers has been observed. Schottky and MIS diodes using ZnSe-I layers have been produced on n-doped epilayers using semitransparent Au-films. Photosensitivities comparable to bulk material have been obtained in spite of a still significant density of defect states. First depositions onto Mo-coated 7095 glass substrates have also been achieved, resulting in highly 111-oriented polycrystalline films.<>