Recent Research Trends in Point Defects in Copper Iodide Semiconductors

Copper iodide is a transparent p -type semiconductor that can be applied in thin-film transistors, transparent conductors, and light-emitting devices. Point defects affect the semiconductor properties of copper iodide. Therefore, many researchers have attempted to reveal the properties of point defects in copper iodide. A typical optical property related to point defects is photoluminescence (PL). PL peaks (430 nm and 700 nm) derived from defects have been reported for single-crystalline copper iodide. Density functional theory (DFT) studies reveal that the most stable defect species is the copper vacancy ( V Cu ). These studies report that PL energies and defect species can be associated using experimental and DFT analyses. Researchers have also introduced defects into copper iodide single crystals or thin films artificially by controlling the annealing atmosphere and observed the relationship between the PL or absorption energy and Cu/I ratio. A comparison of this result with DFT results revealed that the photoactive defects were copper vacancies ( V Cu ), iodine vacancies ( V I ), and iodine ions substituted at copper sites (I Cu ). Elucidation of the origin of fluorescence and coloration has enabled active control of optical properties via synthesis conditions. However, more drastic control of optical or electrical properties by doping is required for fabrication of actual devices. Some DFT studies on chalcogen doping have been reported; however, more theoretical and experimental studies are required.