Hole transport and doping states in epitaxial CuIn1−xGaxSe2

Abstract

Temperature dependent mobility, resistivity, and carrier concentration measurements were made on epitaxial single crystal thin films of group III-rich CuIn1−xGaxSe2 (CIGS). The films were produced using a hybrid sputtering and evaporation process on GaAs substrates. Samples with average Ga/(In+Ga) values between 0.03 and 1.0 and Cu/(In+Ga) between 0.73 and 1.00 were measured. All films were p type with room-temperature carrier concentrations between 4×1016 and 2×1019 cm−3. Fits to electrical measurements were consistent with the presence of two acceptor levels, with activation energies of 167±20 and 42±8 meV at low Ga contents, and compensating donors in all samples. Increasing Ga content was found to increase acceptor density and decrease acceptor level depth. Hole mobilities near room temperature were found to be between 167 and 311 cm2/V s and peak mobilities were between 439 and 1760 cm2/V s. Mobility behavior did not change significantly as a function of composition or the presence of a Ga gradient.