Structure and optoelectronic properties of single crystal epitaxial Cu(In1-xGax)Se2 and ordered defect compounds

Epitaxial CuIn_1-xGa_xSe₂ was grown on As-terminated (111) GaAs between 550 to 735°C with 0⩽x⩽1. The Cu/[In+Ga] ratio, y, ranged from y=0.3 to 1.3. Analysis of the deposited films showed an ordered defect structure that was homogeneous throughout the epitaxial layers when group III rich for all Ga contents examined. Films grown with y=0.3 had energy gaps of ~1.2 eV and showed evidence by both cathodoluminescence and optical absorption of band tails. Stacking faults affect both the growth rate and the luminescence but can be converted to dislocations by rapid thermal annealing. The highest hole mobilities to date, >1500 cm²/V-sec, were measured at 50-75 K by Hall-effect in near-stoichiometry samples. Room temperature hole mobilities were >200 cm²/V-sec and increased at low temperatures. Hole concentrations showed evidence of a level 80 meV above the valance band edge at a concentration in excess of 10¹⁷ cm^-3 in all p-type samples. A composition-dependent level at ~40 meV and type conversion at ~100 K was also observed