Band-inverted gaps in InAs/GaSb and GaSb/InAs core-shell nanowires

Abstract

The [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires have been studied by the 8 × 8 Luttinger-Kohn Hamiltonian to search for non-vanishing fundamental gaps between inverted electron and hole bands. We focus on the variations of the band-inverted fundamental gap, the hybridization gap, and the effective gap with the core radius and shell thickness of the nanowires. The evolutions of all the energy gaps with the structural parameters are shown to be dominantly governed by the effect of quantum confinement. With a fixed core radius, a band-inverted fundamental gap exists only at intermediate shell thicknesses. The maximum band-inverted gap found is ~4.4 meV for GaSb/InAs and ~3.5 meV for InAs/GaSb core-shell nanowires, and for the GaSb/InAs core-shell nanowires the gap persists over a wider range of geometrical parameters. The intrinsic reason for these differences between the two types of nanowires is that in the shell the electron-like states of InAs is more delocalized than the hole-like state of GaSb, while in the core the hole-like state of GaSb is more delocalized than the electron-like state of InAs, and both favor a stronger electron-hole hybridization.

Exploring Strategies toward Synthetic Precision Control within Core–Shell Nanowires

“…Moreover, from a theoretical perspective, reports have surfaced on the influence and effects of shell strain and geometric parameters (such as shell thickness) on the valence band structure and transport properties of not only semiconducting III–V systems but also related alloyed materials . The dependence of the effective gap on variables, such as the core radius and NW shell identity, has been postulated within semiconducting core–shell NWs . As such, being able to readily relate geometric and material properties, including not only mismatch strain between the core and shell but also shell thickness, with measurable observables, such as optical photoluminescence, elasticity, magnetic behavior, , and electron mobility, would be intrinsically useful in acquiring consequential structure–property correlations.…”

“…45 The dependence of the effective gap on variables, such as the core radius and NW shell identity, has been postulated within semiconducting core−shell NWs. 46 As such, being able to readily relate geometric and material properties, including not only mismatch strain between the core and shell 47 but also shell thickness, 48 with measurable observables, such as optical photoluminescence, elasticity, 49 magnetic behavior, 50,51 and electron mobility, 52 would be intrinsically useful in acquiring consequential structure−property correlations. Yet, at a basic level, reports on the facile, large-scale synthetic protocols that can fabricate homogeneous, monodisperse core−shell structures at gram and kilogram levels are few and far between, meaning that a thorough and comprehensive characterization of these materials is limited by the simple fact of not having enough quantities of sample to work with.…”

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

“…Single-band descriptions have been widely used, including non-perturbative electric and magnetic fields [18,[25][26][27]. Multi-band k • p descriptions, which include spin-orbit coupling arising from valence states are crucial to describe, e.g., optical properties [28,29], have been employed for several classes of materials, taking into account composition modulations, crystallographic details and mesoscopic symmetries [30][31][32][33][34][35][36]. Spin-orbit coupling in the conduction band has been evaluated, also in presence of strong magnetic fields [37][38][39].…”

Band structure and end states in InAs/GaSb core-shell-shell nanowires

“…In addition to the QWs, InAs/GaSb core-shell nanowires (NWs) have been investigated both experimentally and theoretically. [5][6][7][8][9][10][11][12][13][14][15] Core-shell NWs with one shell are grown by several groups today, [8][9][10][11][12][13][14][15][16] and NWs with two shells can be grown, 16 e.g., for the reason of a passivating outer layer on InAs. 14 In this work we study core-shell-shell NWs, where an insulator core is radially overgrown with one InAs and one GaSb layer, see Fig.…”