Intermediate band formation, band gap tuning and optical response of transition metal doped CuGaS2 chalcopyrite: A first-principles strategy

We have reported first-principles investigation on formation of intermediate energy bands (IEBs), band gap tunning, optical response and origin of magnetism in TM-doped chalcopyrite CuGa_1-xTM_xS₂ (TM = Cr, V, and Ti; x = 0.06, 0.12, and 0.50) using the full potential augmented plane wave (FP-LAPW) method within the framework of density functional theory. The Tran-Blaha modified Becke-Johnson (mBJ) exchange-correlation potential have been employed in computations. CuGa_0.5Cr_0.5S₂ and CuGa_0.5Ti_0.5S₂ chalcopyrites found to have metallic nature. 6 % Ti and 12 % V-doped CuGa_1-xTM_xS₂ chalcopyrite have showed direct band gap. 6 % V-doped CuGa_1-xTM_xS₂ have showed higher band gap value while the lowest band gap has been observed for 12 % Cr-doped CuGa_1-xTM_xS₂. Increase in concentration of TM atom up to 12 % reduces the band gap value and increases the number of the IEBs. It is seen that higher doping concentration (50 %) of TM atoms ceases the formation of IEBs. Cr-doped CuGa_1-xTM_xS₂ chalcopyrites have shown higher spin magnetic moments than V- and Ti-doped CuGa_1-xTM_xS₂. Further, it is seen that d-states of the TM atom is responsible for magnetism in CuGa_1-xTM_xS₂. Based on optical properties, CuGa_0.88V_0.12S₂, CuGa_0.5V_0.5S₂ and CuGa_0.88Ti_0.12S₂ chalcopyrites have shown higher integrated absorption coefficient than the bulk silicon depicting prominent materials for photovoltaic and opto-electronic devices. Also, studied CuGa_1-xTM_xS₂ have depicted good absorber of the ultra-violet radiation.