Intrinsic defects in p-type transparent conductor CuI: A first-principles study

γ-CuI is a p-type semiconductor material with a small effective hole mass that is widely used in photodetectors, solar cells, and electronic devices. The introduction of intrinsic defects is inevitable during material preparation. This study computationally investigated the optoelectronic properties of CuI containing intrinsic defects. The calculated results reveal that the bandgap of pristine bulk CuI is 0.805 eV, while systems incorporating V_Cu (copper vacancy), V_I (iodine vacancy), Cu_i (copper interstitial), I_i (iodine interstitial), Cu_I (copper-on-iodine antisite), and I_Cu (iodine-on-copper antisite) defects exhibit bandgaps of 1.204 eV, 0.106 eV, 1.375 eV, 0.102 eV, 1.196 eV, and 1.375 eV, respectively. All the systems are direct-bandgap semiconductors. Specifically, the CuI defect introduces deep levels within the forbidden band, which facilitates accelerated electron-hole pair recombination but has a minimal impact on the carrier concentration of CuI. Furthermore, the elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and mechanical stability were examined. Both pristine CuI and systems with Cu_i, Cu_I, I_Cu, and V_I defects exhibited B/G ratios greater than 1.75 and Poisson's ratios (υ) greater than 0.26, indicating good ductility. Analysis based on ionization energy differences suggests that I_i, V_Cu, and Cu_I defects exhibit p-type conductivity tendencies.