Band offsets in InP/ZnSe nanocrystals evaluated using two-photon transitions analysis

TL;DR

This paper provides a theoretical analysis of energy structures and optical transitions in InP/ZnSe nanocrystals, revealing how band offsets influence two-photon absorption and exciton states, with implications for understanding heterointerface properties.

Contribution

It introduces a semi-analytical kp-model to evaluate band offsets and optical spectra in InP/ZnSe nanocrystals, incorporating Coulomb interactions and exciton analysis.

Findings

Valence band offset range is 0.85-1 eV depending on strain.

Transition to ground two-photon exciton can be hidden by higher states.

Electric dipoles at the heterointerface are indicated by offset analysis.

Abstract

We present a semi-analytical theoretical kp-study of the energy structure and optical transitions in spherical core-shell InP/ZnSe nanocrystals. We use the eight-band Kane model and the six-band Luttinger Hamiltonian in the spherical approximation to calculate the electron and hole energy spectra, respectively. The influence of the Coulomb interaction is considered perturbatively. The one- and two-photon absorption spectra are calculated as functions of the band offsets between the InP core and ZnSe shell. Exciton states responsible for the main features in the two-photon absorption spectra of InP/ZnSe nanocrystals are identified and the spectral dependence of the linear-circular dichroism signal is predicted. We show that in the presence of inhomogeneous broadening, the transition to the ground two-photon-active exciton state can be hidden behind intense transitions to higher-lying states. A comparison of the calculated one- and two-photon absorption spectra with the available experimental data shows that, depending on the lattice strain in the InP core, the range of possible valence band offsets is 0.85-1 eV. The determined range exceeds the natural valence band offset of 0.57 eV and indicates the presence of electric dipoles formed by the preferential Zn-P bonds at the InP/ZnSe heterointerface.