Optical properties of single crystalline copper iodide with native defects: Experimental and density functional theoretical investigation

摘要

Copper iodide (CuI) is an attractive transparent p-type semiconductor, and we investigated the relationship between the optical property and native defects in CuI using experimental and theoretical studies. To exclude neither surface impurity nor interface strain, we used well-defined CuI single crystals with native defects, i.e., Cu-rich CuI and I-rich CuI, as well as highly pure CuI, which were prepared by post-annealing treatment of the CuI single crystal under controlled atmosphere. The optical absorption and photoluminescence (PL) properties of these samples were then carefully evaluated. Consequently, two absorption signals (AB1: 2.9 eV, AB2: 2.7 eV) and two PL peaks (PL1: 2.9 eV, PL2: 1.8 eV) were observed. The AB1, AB2, and PL1 signals were obvious under I-rich conditions, whereas the PL2 signal was dominant in the Cu-rich sample. To discuss the origin of these absorption and PL signals, we calculated the absorption and emission energies of defects in CuI using the density function theory (DFT). As a result, AB1 and PL1 are assigned to the transition and recombination between copper vacancy (V-Cu) and conduction band, while PL2 is assigned to the recombination from the iodine vacancy (V-I) to the valence band. Most interestingly, AB2 is presumed to be due to the transition from the valence band to antisites of iodine substituted for copper (I-Cu), which can be reasonably explained by the off-center model of substituted iodine ions. This work will contribute to developing and understanding optoelectrical devices using CuI. Published under license by AIP Publishing.