Near-surface electronic defects and morphology of CuIn1ÀxGaxSe2

CuIn12xGaxSe2 ~CIGS! is a leading candidate for high-efficiency solar cells, yet the defects and electronic structure that define performance are relatively unexplored. We employed low-energy depth-resolved cathodoluminescence to measure the local band and defect properties of epitaxial CIGS films having ~002!, ~220!/~204!, or ~112! orientations on GaAs substrates. Along with a near-band-edge emission, room-temperature luminescence spectra for all epitaxial samples reveal a well-defined deep-level transition confined within ;100 nm of the surface. The intensity of this defect-related feature reaches a maximum at the surface relative to the near-band-edge peak. Polycrystalline CdS/CIGS/Mo/glass and CIGS/Mo/glass solar-cell layers were also studied. These exhibit a weaker deep-level emission modulated by CIGS-thickness-related optical cavity effects. The integrated intensity of this emission relative to the near-band-edge peak intensity is also a maximum at the surface and decreases into the sample. A strong deep-level emission due to CdS was also observed decaying with depth relative to the near-band-edge emission of the CIGS. The CdS emission was the only significant change in the polycrystalline emission spectrum with and without the CdS layer. The observed behavior is consistent with the existence of a nanoscale near-surface defective region whose properties can impact charge generation and recombination in solar energy-generating structures. © 2002 American Vacuum Society. @DOI: 10.1116/1.1526357#