Abstract
We report excitonic properties of the PbI 2 thin films with a thickness of 2 to 50 v; nm grown on (0001) Al 2 O 3 and (001) NaCl substrates by vacuum deposition. From the substrate-temperature dependence of absorption spectra, it is found that the crystal structure of the 50-nm thin film on the Al 2 O 3 substrate changes from 2 v; H to 4 v; H type by a thermally induced transition at a substrate temperature around 160 v; °C. However, such a crystal-structure change does not occur for the NaCl substrate, where the crystal structure remains 4 v; H type. For PbI 2 thin films whose thickness is thinner than 5 v; nm, the individual confinement effects on electrons and holes cause a high-energy shift in the exciton energy with a decrease in the film thickness. Absorption spectra of PbI 2 thin films with a thickness of 8 to 15 v; nm exhibit oscillatory structures due to the quantization of the translational motion of the exciton.