Opto-transport properties of e-beam evaporated annealed CuInSe2 thin films

This work illustrates thickness dependent physical properties of copper indium diselenide CuInSe2 (CIS) thin films fabricated by a novel two stage electron-beam evaporation technique. Structural analysis exhibits CuInSe2 phase chalcopyrite structure having preferred orientation in the (112) plane. Absorption coefficient of CIS films have been found very high and associated with band-to-band transition. The optical band gap displays a slight variation from 1.80 eV to 1.90 eV depending on film thickness. Photoluminescence (PL) study reveals the presence of acceptor-type defects in the films. Some other important optical constants, such as refractive index, real and imaginary parts of dielectric constant, optical conductivity and energy loss function are also calculated and found dependent on film thickness. Electrical conductivity measurement confirms CIS films are semiconducting in nature and the activation energy values indicate electrical transport is mainly thermally activated. Hall Effect study confirms CIS films are p-type having carrier concentration of the order of ∼1026 m-3.