Energy spectrum, density of states and optical transitions in strongly biased narrow-gap quantum wells

TL;DR

This paper theoretically investigates how strong electric fields influence the electronic and optical properties of narrow-gap lead salt quantum wells, enabling control over their energy spectrum and potentially enhancing optical absorption.

Contribution

It introduces a model showing electric field-induced transition of narrow-gap quantum wells to nearly gapless 2D systems with linear dispersion relations.

Findings

Electric field controls the energy gap in quantum wells.

Strong fields induce a nearly gapless 2D electron spectrum.

Density of states exhibits inverse-square-root divergences at edges.

Abstract

We study theoretically the effect of an electric field on the electron states and far-infrared optical properties in narrow-gap lead salt quantum wells. The electron states are described by a two-band Hamiltonian. An application of a strong electric field across the well allows the control of the energy gap between the two-dimensional (2D) states in a wide range. A sufficiently strong electric field transforms the narrow-gap quantum well to a nearly gapless 2D system, whose electron energy spectrum is described by linear dispersion relations \epsilon_{\sigma} (k) ~\pm (k-k_{\sigma}), where k_{\sigma} are the field-dependent 2D momenta corresponding to the minimum energy gaps for the states with spin numbers \sigma. Due to the field-induced shift of the 2D subband extrema away from k=0 the density of states has inverse-square-root divergencies at the edges. This property may result in a considerable increase of the magnitude of the optical absorption and in the efficiency of the electrooptical effect.