Characterization of Cr Doped CuGaS2 Thin Films Synthesized By Chemical Spray Pyrolysis

Addition of an impurity or intermediate band in a semiconductor can extend its optical functionalities to novel application such as intermediate band solar cells (BSCs). For this purpose, the optical and electronic characterization were performed on Chromium (Cr) doped (1-4%) chalcopyrite CuGaS2 (CGS) thin films synthesized by chemical spray pyrolysis technique on glass substrates. The structural and chemical characterization studied in the past confirmed that the prepared films are in tetragonal chalcopyrite structure with polycrystalline nature [1]. In the present study, electronic transitions studied by photo-modulated reflectance (PR) measurements showed widened bandgaps when Cr was added, and agrees well with our calculation based on density functional theory (DFT). Native defect-related transitions typically observed within the bandgap of the host CGS semiconductor were reduced in the Cr added films. This observation is consistent with photo-luminescence (PL) spectra measured at room temperature. An additional signature of an impurity band emerged in the PR transitions for Cr-added samples. Analysis of spin-resolved density of state calculation suggests that the IB originates from spin-polarized bands.