Growth and characterization of CuxAg1-xInSe2 thin films by pulsed laser deposition

Abstract

We report on structural and optical measurements made on thin films of the quaternary compounds CuxAg1-xInSe2(x = 0; 0.3; 0.5; 0.7; 1.0). The films were prepared by pulsed laser deposition (PLD) of prereacted material onto glass substrates. The substrate temperature was about 450-480 degrees C. The beam of a Nd:YAG laser was directed onto a rotating target. The resulting films were characterized by XRD, SEM, and EDAX, The films were single phase, polycrystalline and stoichiometric within 4 %. The refractive index n and the absorption coefficient alpha of CuxAg1-xInSe2 thin films were obtained by measuring the transmittance (T) and reflectance (R) in the photon energy range from 0.4 to 2.5 mu m. The optical properties were determined from rigorous expression for the transmission and reflection in an air/film/glass substrate/air multilayer system. The films had high optical absorption about 10(4) - 10(5) cm(-1) and the band gaps of 0.99 eV (CuInSe2) and 1.25 eV (AgInSe2). The energy gaps observed in laser-deposited CuxAg1-xInSe2 thin films near and above the fundamental absorption edge exhibit a nonlinear composition dependence.