[17a-D419-1~12] 6.4 Thin films and New materials

[17a-D419-10] Two-dimensional exciton confinement effect in thickness-controlled PbI₂ thin films

〇Masao Nakamura¹, Ryuichi Namba², Takahiro Yasunami², Naoki Ogawa^1,2, Yoshinori Tokura^1,2,3, Masashi Kawasaki^1,2 (1.RIKEN-CEMS, 2.Univ. of Tokyo, 3.Tokyo College)

Keywords:layered compound, exciton, 2D confinement effect

In this study, we investigated the two-dimensional exciton confinement effect in a layered semiconductor PbI₂ with a direct bandgap_. We synthesized epitaxial thin films of PbI₂ with precisely controlled thicknesses by molecular beam epitaxy. The absorption spectra of the thin films showed oscillatory structures indicating the exciton center-of-mass quantization. Furthermore, the quantization energy showed a considerable blue shift when the thickness is below 5 atomic layers due to the strong confinement effect. This is the first observation of a crossover between the strong and weak confinement effects in layered compounds.