Ionized cluster beam deposition of GaAs thin films for solar cells

Polycrystalline GaAs films have been deposited by means of an ion-assisted deposition process at a technical vacuum of 10^-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 10¹³/cm³, 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°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