Linear and nonlinear optical properties of CuInSe2 and CuGaSe2 epitaxial thin films on GaAs(001)

The linear and nonlinear optical properties of tetragonal CuInSe2 and CuGaSe2 thin films grown epitaxially on GaAs(001) have been investigated as a function of film stoichiometry. The refractive indicies of the films have been measured between 250 and 800 nm using ellipsometry. For a fundamental wavelength of 790 nm, the second order optical nonlinearity χ(2) and optical third harmonic field anisotropy σ are typically reduced strongly in nonstoichiometric thin films and correlate well with each other. The magnitudes of the chalcopyrite film χ(3) values are relatively small, being typically only ∼1% of those of Si. Third harmonic data from an approximately stoichiometric CuInSe2 thin film is consistent with a significant second order surface optical nonlinearity cascading contribution. Spectral features in the room temperature refractive index data from approximately stoichiometric CuInSe2 and CuGaSe2 thin films correlate well with previous experimental work.