On Wannier exciton 2D localization in hydrogen intercalated InSe and GaSe layered semiconductor crystals

Abstract

Exciton absorption spectra of layered InSe and GaSe crystals electrochemically intercalated by hydrogen were investigated. It was found that the observed at T = 80 K non-monotonic shift of the exciton absorption peak n = 1 with growing hydrogen concentration x (here x is the amount of hydrogen atoms per a formula unit of a crystal matrix) stems from the increasing dielectric permittivity of the crystal ε₀ due to availability of hydrogen in the van der Waals gap. Growth of ε₀(x) results in decrease of the exciton binding energy but, at larger x concentrations (when the anisotropy parameter ε*(х) grows), 2D localization of exciton motion in the crystal layer plane takes place, which causes reduction and then, at x > 1, stabilization of sizes both for the exciton and quantum well.