Hole Concentration Reduction in CuI by Zn Substitution and its Mechanism: Toward Device Applications

Abstract

Copper iodide (CuI) is a promising p-type transparent semiconductor with excellent carrier mobility. However, the high hole concentration in conventionally fabricated CuI including the single crystal hinders its applicability to the channel layer of thin-film transistors. We found that Zn substitution into Cu+ sites can effectively reduce the hole concentration. Experimental and computational examinations showed that the dominant mechanism involved the formation of a defect pair, the Zn-substituted Cu site (Zn-Cu) and Cu vacancy (V-Cu), and the simultaneous suppression of V-Cu arising from the stabilization of Cu+ in the Zn-substituted CuI lattice, rather than hole compensation by the electrons generated from Zn2+ substitution into Cu+ sites. Our results show that the hole concentration of Zn-substituted CuI is tunable in the range of 1014-1018 cm-3, making it suitable for thin-film transistors and hole transport layers in OLEDs.