Investigation of the (Cu, Ga) InSe2 thin film with different pairs of CuGa/In sputtered layers

Abstract

Thin film samples of (Cu,Ga) InSe2 (CIGS) were prepared by DC magnetron sputtering and the selenisation process onto soda lime glass substrates. All samples had the same deposition conditions, and the optimal sputtering thickness of samples with one CuGa/In pair and two CuGa/In pairs are also the same. After sample deposition, X-ray diffraction (XRD), scanning electron microscope (SEM) and Hall effect measurements were used to characterize the properties of these samples. From XRD measurement results, excepting an extra small CuSe peak existing in the samples with two CuGa/In pairs, the XRD peaks of all samples are perfectly matched with the phase diagram of CuGa0.3In0.7Se2 material. It was also found that the grain sizes of the samples with one CuGa/In pair are larger than those with two CuGa/In pairs from SEM images. All these observations on samples with two CuGa/In pairs can be attributed to the fact that the less In incorporation in CIGS films, which it has been proven that the sample with low In-to-CuGa ratio has stronger CuSe peak from XRD result. Furthermore, the p-type carrier characteristics can be observed for all samples from Hall measurement results. The carrier mobility and concentration of the samples with one CuGa/In pair can be achieved as high as 15.28 cm(2)/Vs and as low as 1.50x10(16) cm(-3), respectively, while the carrier mobility and concentration of the ones with two CuGa/In pairs can be achieved as 6.4 cm(2)/Vs and 6.27x10(17) cm(-3), respectively. The results of superior electrical properties of samples with one CuGa/In pair agree well with the observations form XRD and SEM results. In the final, the optimal value of In-to-CuGa ratio during CuGa/In layers deposition in this study is 0.625.