Estimation of Stress in Polycrystalline CuInSe2 Films Deposited on Mo‐Coated Glass Substrates

TLDR: In this paper, the authors measured the optical reflectance spectra of polycrystalline thin films of CuInSe 2 deposited on soda-lime glass and Mo-coated glass substrates by utilizing the broadening of the optical absorption band tail.

Abstract: Stress and strain in polycrystalline thin films of CuInSe 2 deposited on soda-lime glass and Mo-coated glass substrates were determined from the optical reflectance spectra by utilizing the broadening of the optical absorption band tail. The contributions of both intrinsic (due to grain boundary and lattice vibrations) and extrinsic stresses (due to thermal mismatch of film and substrate) were considered. It was observed that the films deposited on Mo-coated glass substrates had lower grain size and higher stress (3 x 10 7 Pa) compared to those of the bare glass substrates (1.1 x 10 7 Pa). This process of estimation of mechanical properties of thin films from optical measurements on both absorbing (Mo/glass) and non-absorbing (glass) substrates appears to be very attractive due to its non-destructive nature. The defect state density (Q t ) at the grain boundary region along with the internal built-in average electric field (F av ) were determined with the variation of the Cu/In ratio in the films, deposited on glass and Mo-coated glass substrates. It was observed that both Q t and F av were higher for Cu/In < 1.0 and decreased as the stoichiometric composition was approached.