Investigation of intermediate impurities on high quality AgGaS2 single crystal grown by vertical gradient freezing method

•XRD, EDS and FTIR results manifest that high quality AgGaS2 single crystal were obtained by VGF method.•XPS was proposed as suitable method to study fairly low content of intermediate impurities on AgGaS2 polycrystal and single crystals.•Origins of intermediate impurities and their changes of varieties and content from AgGaS2 polycrystal to single crystal were studied. In this study, intermediate impurities on synthesized AgGaS2 polycrystal and grown AgGaS2 single crystal were studied by X-ray photoelectron spectroscopy (XPS) which was recommended as workable method to characterize intermediate impurities on AgGaS2 while the content of those impurity components were too low to be detected using common X-ray diffraction (XRD) measurement. Meanwhile, XRD, Energy Dispersive Spectrometer (EDS) and Fourier-transform infrared spectrophotometry (FTIR) were employed to characterize the quality of AgGaS2 crystals. The results manifest that AgGaS2 crystal with high infrared transmittance and good uniformity were successfully obtained. However, XPS results indicate that intermediate impurities with different content and varieties exist on both AgGaS2 polycrystal and AgGaS2 single crystal respectively and decrease of intermediates may lead to improvement of its optical property.