Tuning the properties of exciton complexes in self-assembled GaSb/GaAs quantum rings

Abstract

Type-II self-assembled GaSb/GaAs nanostructures have been grown by molecular-beam epitaxy and studied by atomic-force microscopy, transmission electron microscopy, and power-dependent magnetophotoluminescence. Nanostructures on the sample surface are found to be entirely dotlike, while capped nanostructures are predominantly ringlike. Moreover, an in situ anneal process applied after thinly capping the dots is shown to enhance the severity of the rings and relax the strain in the matrix in the proximity of the GaSb, resulting in a change to the spatial configuration of the exciton complexes and their optical properties.

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

“…For memory applications, which generally require long storage times, the QDs should have a large hole localization energy. This property depends strongly on the shape and composition of a QD, 11 thereby making detailed knowledge of the morphology important for future applications of these QDs.…”

“…These results confirm previous studies performed by atomic force microscopy, where measurements on uncapped GaSb/ GaAs nanostructures show only dots with no indication of holes in the center or other forms of dot demolition. 11,17 For 112 nanostructures grown under similar growth conditions, the base width has been determined (see Fig. 4).…”

Hole migration and optically induced charge depletion in GaSb/GaAs wetting layers and quantum rings

“…XTEM images of GaSb/GaAs samples have shown that large single-lobed GaSb structures (QDs) have much more strain in the surrounding GaAs matrix than smaller double-lobed structures (QRs). 30 This high strain is further evidenced by the tendency for screw dislocations to form in the GaAs layer above the QDs. 31 Calculations of the band structure of different sized GaSb/GaAs QDs have shown that for large, highly strained QDs, there is a significant increase in the conduction band minimum energy of the GaAs close to the QD.…”

“…Indeed, the magneto-PL measurements of Ref. 30 found that differences in growth conditions, and thus QR morphologies, can tune the excitonic properties of such nanostructures. It was shown that QRs with larger inner radii have less strain in the surrounding GaAs, allowing electrons much closer to the holes in the QRs.…”

Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

“…The GaAsSb single quantum wells grown by MLE on the (111)A and (110) substrates exhibit type-II band alignment, and a very abrupt heterostructure was expected. GaSb quantum dots [133][134][135][136][137][138] and rings [139,140] formed on GaAs or embedded in a GaAs matrix have been reported, and the MLE growth and optical properties of GaSb dots have been investigated [132]. Figure 19 shows atomic force microscope (AFM) images of GaSb dots for different substrate orientations.…”