Sputter deposited ZnTe/ZnSe/ZnO heterojunctions for photovoltaic applications

Films of ZnTe, ZnSe, and ZnO were deposited on (100) Si by RF magnetron sputtering from stoichiometric ZnTe, ZnSe, and ZnO targets for the purpose of fabricating a ZnTe/ZnSe heterojunction. Rutherford back scattering (RBS) analysis yielded a composition of Zn_1.0Te_1.0 for ZnTe, Zn_1.1Se_1.2 for ZnSe, and Zn_1.0O_0.8 for ZnO which indicates that near-stoichiometric films were obtained. Transmission electron microscopy (TEM) of cross-sectional samples established that the films were polycrystalline in nature. Heterostructures were grown on ZnO coated low resistivity n-type Si wafer. The heterojunctions consisted of a ~65 nm layer of ZnSe, to serve as an absorber layer and ~40 nm of ZnTe as a window layer. The heterojunction wafer was diced into 1 cm² samples. A Pt back contact was deposited on the Si. The top surface of the junction was patterned with a contact leaving two, 0.25 cm × 0.65 cm ZnTe windows exposed. Both the top and bottom contacts were annealed at 350°C under N₂ atmosphere for 5 min. Under 120 W halogen lamp illumination the junction showed a photovoltaic response. Between the top Al and back Pt, the device produced an approximate open-circuit voltage (V_OC) of 600 mV as measured with a high impedance voltmeter.