Second-harmonic generation from CuInSe/sub 2/ thin films: influence of the substrate-epilayer lattice mismatch

We investigate the second-order nonlinear optical (NLO) properties of tetragonal chalcopyrite-structure CuInSe/sub 2/ thin films using optical second-harmonic generation at a fundamental wavelength of 790 nm. An approximate doubling of the second-order optical nonlinearity of the CuInSe/sub 2/ thin films is achieved through changing the substrate from GaAs[001] to In/sub 0.29/Ga/sub 0.71/As[001], thereby reducing the lattice mismatch from 2.2% to 0.2%. This observation suggests that minimizing the lattice mismatch is a key requirement for the growth of high-quality NLO active chalcopyrite structure thin films and is in contrast to some other NLO active thin-film systems.