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

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.