Novel Capacitance Measurements in Copper Indium Gallium Diselenide Alloys: Final Subcontract Report, 1 July 1999--31 August 2003

Abstract

This subcontract report describes the University of Oregon's objectives to measure the electronic properties of the copper indium/gallium diselenide alloys using several well-developed capacitance techniques appropriate for probing materials with a continuous distribution of semiconducting gap electronic energy states. We applied a new synthetic method to the production of CIGS alloys, namely, the modulated elemental reactant method. To form CIGS by this method, alternating layers of Cu:In:Se and Cu:Ga:Se composites, each less than 100 thick, were evaporated in sequence and then annealed at low temperature. A second focus was to test and develop junction capacitance methods to better understand the electronic properties in CIGS material and establish a relationship of those properties to specific device performance parameters. The primary methods employed were transient photocapacitance (TPC) spectroscopy and drive-level capacitance profiling (DLCP). Finally, we extended our characterization studies to four CuIn1-xAlxSe2 (CIAS) samples, also supplied by IEC. Our photocapacitance and DLCP measurements on these CIAS samples indicated that for a sample with 13 at.% Al (having a bandgap of nearly 1.2 eV), the electronic properties were essentially identical to those in CIGS samples with 26 at.% Ga.