Structure and optoelectronic properties of single crystal epitaxial Cu(In/sub 1-x/Ga/sub x/)Se/sub 2/ and ordered defect compounds

Epitaxial CuIn/sub 1-x/Ga/sub x/Se/sub 2/ was grown on As-terminated (111) GaAs between 550 to 735/spl deg/C with 0/spl les/x/spl les/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 /spl sim/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 cm/sup 2//V-sec, were measured at 50-75 K by Hall-effect in near-stoichiometry samples. Room temperature hole mobilities were >200 cm/sup 2//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 10/sup 17/ cm/sup -3/ in all p-type samples. A composition-dependent level at /spl sim/40 meV and type conversion at /spl sim/100 K was also observed.