The defect chalcopyrite material CuIn3Se5 has been identified as playing an essential role in efficient photovoltaic action in CuInSe2-based devices; it has been reported to be of n-type conductivity, forming a p-n junction with its p-type counterpart CuInSe2. Because the most efficient cells consist of the Cu(In1-xGax)Se2 quaternary, knowledge of some physical properties of the Ga-containing defect chalcopyrite Cu(In1-xGax)3Se5 may help us better understand the junction phenomena in such devices.
Polycrystalline Cu(Inl-xGax)3Se5 (with O<x<l) thin films have been grown on 7059 Coming glass, soda-lime silica glass, n-type (100)Si, and Mo-coated soda-lime glass by coevaporation from elemental sources. In general, optical data show direct optical bandgaps that range from 1.20 eV for x=0 to ∼1.85 eV for x=l (this represents ∼200 meV higher bandgaps than the Cu(In, Ga)Se2 counterparts). Micrographs of the thin films show a substantial change in morphology as the Ga content is increased—for identical conditions of growth rate and substrate temperature. X-ray diffraction patterns agree with previously publish data for the ternary case (x=0), where these materials have been referred to as ordered vacancy compounds. Pole figures confirm a high degree of texturing in the films and a change in preferred orientation as Ga content is increased.