The Preparation, Doping And Optical Properties Of Cums₂（M=in,Ga） Thin Films

Copper gallium disulphide (CuGaS2, CGS) thin films were successfully prepared by sulfurising Cu-Ga precursors in sulfur atmosphere which have been obtained through magnetron sputtering. First, the magnetron sputtering conditions were chosen as following:pressure (1.0Pa), time (30min) and sputtering power (15,30,45,60,80and100W, respectively). Finally, a proper atomic ratio of the precursor was found to be sulfurized easily with a sputtering power of30W. Second, sulfurization of the precursor films was carried out at different temperatures (450,500,550and600℃). Structural, chemical composition and optical properties of CGS films were analyzed by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), scanning electron microscopy and UV-vis spectrophotometer. The results indicated that the CuGaS2films with a single-phase structure had formed at450℃and the crystallinity of this phase was improved as the temperature rising. The compositions of the films were Cu-rich, poor in Ga and S, containing mainly CuGaS2chalcopyrite phase (I42d). And the crystal lattice parameters were a=b=5.3544A and c=10.4707A at a sulfurization temperature of600℃. The UV-vis spectroscopy indicated that the values of band gaps are2.3leV,2.34eV,2.40eV and2.46eV within the temperature increasing from450to600℃. So the CuGaS2with wide band gap is the best host to accommodate an isolated narrow intermediate band for photovoltaic applications. The Ti-doped CuGaS2thin films are obtained in the same ways. The successful doping of Ti is also evidenced by a left shift of XRD peaks. The corresponding band gaps of CuGaS2are2.27eV (0.53at.%Ti-doped),1.98eV (0.82at.%Ti-doped).The particles of Sn-doped CuMS2(M=In,Ga) thin films were harvested by ball-milling different powders dispersed in ethanol, spin-coating the slurry on SiO2substrates and annealing the precursor thin films in Ar atmosphere at600℃for20min. In the XRD patterns the diffraction peaks were all indexed to a chalcopyrite structure (I42d). The successful doping of Sn is also evidenced by a right shift of XRD peaks in CuIni-xSnxS2and a left shift in CuGa1-xSnxS2. The composition of the films were all Cu-rich, poor in Ga/In and S. The corresponding band gaps of CuGaS2are2.41eV (0.0at.%Sn-doped),2.01eV (0.41at.%Sn-doped),1.87eV(1.15at.%Sn-doped), and the corresponding band gaps of CuInS2are1.45eV (0.0at.%Sn-doped),1.15eV(0.45at.%Sn-doped),1.04eV(1.22at.%Sn-doped).