Confined States of Individual Type-II GaSb/GaAs Quantum Rings Studied by Cross-Sectional Scanning Tunneling Spectroscopy

Abstract

Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties. Hole confinement energies between 0.2 and 0.3 eV and a type-II conduction band offset of 0.1 eV are directly obtained from the data. Additionally, the hole occupancy of quantum dot states and spatially separated Coulomb-bound electron states are observed in the tunneling spectra.

Photoluminescence studies of individual and few GaSb/GaAs quantum rings

“…For light generation purposes, however, the reduction in electron-hole overlap could be detrimental to operating performance. Fabrication of GaSb/GaAs nanostructures by molecular beam epitaxy (MBE) has been shown to result in the formation of nano-rings, [8][9][10] rather than dots, under specific growth conditions. GaSb quantum rings [ Fig.…”

“…GaSb quantum rings [ Fig. 1(a)] have recently been studied in bulk optical measurements, [9][10][11][12] and found to have some surprising optical properties. Cross-sectional scanning tunnelling microscopy (x-STM) has revealed that the ring geometry can confine the electron's wavefunction in its centre, 13 as illustrated in the band diagram in Fig.…”

The disintegration of GaSb/GaAs nanostructures upon capping

“…[11][12][13][14][15][16][17][18] This redistribution of the QD material upon capping affects the optical properties of the dots by creating large variations in the size and composition of the capped QDs, leading to an undesirable increased photoluminescence (PL) linewidth. 13,16,[19][20][21] Understanding the three-dimensional structure of buried QDs and the subsequent effects on their optoelectronic properties is fundamental to determining ways to either exploit or eliminate changes in shape and/or composition that occur to GaSb/GaAs QDs during capping. Several studies have investigated capped QD composition and morphology by using two-dimensional analytical techniques such as transmission electron microscopy (TEM) 14,16,17 and cross-sectional scanning tunneling microscopy (XSTM).…”

GaSb/GaAs quantum dot formation and demolition studied with cross-sectional scanning tunneling microscopy

“…Previous X-STM studies have shown the structural properties of these QDs grown by metal-organic chemical vapor deposition 7 and droplet epitaxy, 8 the principles behind ring formation, 9 and the spectroscopic features of these QDs. 10 However, the dependence of the QD morphology on the growth parameters was never investigated. For memory applications, which generally require long storage times, the QDs should have a large hole localization energy.…”