Effect of Zn doping on p-type conduction of γ-CuI studied by X-ray fluorescence holography and positron annihilation spectroscopy

Abstract

γ-CuI is a p-type semiconductor with high mobility and chemical stability; it has potential applications as a hole-transport layer in organic solar cells and light-emitting diodes. To clarify the mechanism by which Zn doping controls the p-type conduction in γ-CuI, the types of defects formed in Zn-doped γ-CuI were comprehensively investigated through X-ray fluorescence holography (XFH), positron annihilation lifetime spectroscopy (PALS), coincidence Doppler broadening spectroscopy (CDBS), and density functional theory (DFT) calculations. The XFH demonstrated the presence of Zn atoms at the Cu sites (Zn_Cu). Furthermore, PALS and DFT calculations revealed the presence of isolated Cu vacancies (V_Cu). The CDBS suggested the formation of Zn_Cu–V_Cu defect pairs due to Zn doping. These findings supported that Zn doping suppresses p-type conduction via the formation of Zn_Cu–V_Cu defect pairs, as predicted by previous DFT studies. The combination of XFH, PALS and CDBS experiments and DFT calculations is effective for identifying the defect types in semiconductors.