Band structure of n- and p-doped core-shell nanowires

TL;DR

This paper models the electronic band structure of doped core-shell nanowires using an advanced multi-band approach, revealing how doping influences electron and hole distributions, band coupling, and optical properties.

Contribution

It introduces an 8-band Burt-Foreman k.p Hamiltonian method for heterostructured nanowires, accounting for Coulomb interactions and providing detailed insights into doping effects.

Findings

Formation of quasi-1D electron channels at the core-shell interface in n-doped nanowires.

Heavy-hole/light-hole coupling causes non-parabolic dispersions and mass inversion.

Hole gas forms an isotropic ring-like cloud in p-doped nanowires, with uncoupling and mass inversion at high doping.

Abstract

We investigate the electronic band structure of modulation-doped GaAs/AlGaAs core-shell nanowires for both n- and p-doping. We developed an 8-band Burt-Foreman k.p Hamiltonian approach to describe coupled conduction and valence bands in heterostructured nanowires of arbitrary composition, growth directions, and doping. Coulomb interactions with the electron/hole gas are taken into account within a mean-field self-consistent approach. We map the ensuing multi-band envelope function and Poisson equations to optimized, non-uniform real-space grids by the finite element method. Self-consistent charge density, single-particle subbands, density of states and absorption spectra are obtained at different doping regimes. For n-doped samples, the large restructuring of the electron gas for increasing doping results in the formation of quasi-1D electron channels at the core-shell interface. Strong heavy-hole/light-hole coupling of hole states leads to non parabolic dispersions with mass inversion, similarly to planar structures, which persist at large dopings, giving rise to direct LH and indirect HH gaps. In p-doped samples the hole gas forms an almost isotropic, ring-like cloud for a large range of doping. Here, as a result of the increasing localization, HH and LH states uncouple, and mass inversion takes place at a threshold density. A similar evolution is obtained at fixed doping as a function of temperature. We show that signatures of the evolution of the band structure can be singled out in the anisotropy of linearly polarized optical absorption.