Band alignments in the Cu(In,Ga)(S,Se) 2 alloy system determined from deep-level defect energies

The composition dependence of defect energies in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite semiconductor thin films is investigated by admittance spectroscopy. Alloying CuInSe2 with S increases the energy of the dominant acceptor from 300 meV to approximately 380 meV in CuIn(Se0.4S0.6)2, whereas in the alloy system Cu(In1-xGax)Se2, the acceptor energy remains unchanged over the whole composition range 0≤x≤1. Using the acceptor energy as a reference, we extrapolate the valence-band offsets ΔEV=-0.23 eV for the combination CuInSe2/CuInS2 and ΔEV=-0.04 eV for CuInSe2/CuGaSe2.