ESTIMATION OF STRESS IN POLYCRYSTALLINE CUINSE2 FILMS DEPOSITED ON MO-COATED GLASS SUBSTRATES

Stress and strain in polycrystalline thin films of CuInSe2 deposited o n soda-lime glass and Mo-coated glass substrates were determined from the optical reflectance spectra by utilizing the broadening of the opt ical 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 obser ved that the films deposited on Mo-coated glass substrates had lower g rain size and higher stress (approximate to 3 x 10(7) Pa) compared to those of the bare glass substrates (approximate to 1.1 x 10(7) Pa). Th is process of estimation of mechanical properties of thin films from o ptical measurements on both absorbing (Mo/glass) and non-absorbing (gl ass) substrates appears to be very attractive due to its non-destructi ve nature. The defect state density (Q(t)) at the grain boundary regio n along with the internal built-in average electric field (F-av) were determined with the variation of the Cu/In ratio in the films, deposit ed 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 stoichi ometric composition was approached.