Enhanced growth and properties of non-catalytic GaAs nanowires via Sb surfactant effects

Abstract

We report the effects of antimony (Sb) surfactant on the growth and correlated structural and optical properties of non-catalytic GaAs nanowires (NW) grown by selective area epitaxy on silicon. Strong enhancements in the axial growth with very high aspect ratio up to 50 are observed by the addition of small traces of Sb (1%–2%), contrasting the commonly reported growth limiting behavior of Sb in GaAs(Sb) NWs. The Sb surfactant effect modifies the growth facet structure from a pyramidal-shaped growth front terminated by {1–1–0} planes to a flat (111)B growth plane, that is even further improved by the presence of Si co-dopants. Additional benefits are seen by the substantial change in microstructure, from a heavily defected layer stacking in Sb-free GaAs NWs to a twinned phase-pure zinc blende structure in Sb-mediated GaAs(Sb) NWs. We directly confirm the impact of the altered microstructure on the optical emission and carrier recombination dynamics via observation of long, few-ns carrier lifetimes in the GaAs(Sb) NWs using steady-state and time-resolved photoluminescence spectroscopy.

Sb‐Mediated Tuning of Growth‐ and Exciton Dynamics in Entirely Catalyst‐Free GaAsSb Nanowires

“…As recognized from the micrographs as well as the respective SAD patterns (insets), all samples exhibit pure ZB-phase with rotational twin domains only (ZB-A and ZB-B). This observation agrees well with previous studies of both non-catalytic [28] and catalyst-assisted GaAsSb NWs, [23,25,42] where the addition of Sb was found to inhibit formation of WZ phase and, hence, eliminates polytype intermixing and related stacking defects with hexagonal stacking component as otherwise seen in Sbfree GaAs NWs. [29,42,43] Indeed, it has been understood that the formation of a rotational twin defect in ZB crystals, which originates due to a transition from ZB to WZ structure, can be attributed to the relatively low energy for its formation.…”

“…Note that extremely short crystallites and clusters were not considered in this analysis. In all GaAsSb NW samples, an inverse trend of NW length and diameter is observed which is characteristic of the non‐catalytic growth mode [ 28–31 ] ; specifically, with decreasing d 0 from 120 nm to 20 nm, the GaAsSb NWs show increasing length and decreasing diameter, yielding enhanced aspect ratio. These trends are most pronounced in NW‐arrays with low to intermediate Sb‐BEP, and only vaguely seen in the arrays with highest Sb‐BEP due to the inhibited axial growth.…”

“…[ 24,25,36 ] In stark contrast, our results show that in the limit of small Sb‐molar fraction the axial growth is substantially increased, confirming the recently suspected Sb self‐surfactant effect in non‐catalytic GaAsSb NWs. [ 28 ] For example, as seen in Figure 2a, small Sb‐content of 1.5% yields already a ≈fivefold increase in aspect ratio compared to Sb‐free GaAs NWs, while the enhancement in aspect ratio is even ≈tenfold for further increased Sb‐content of 3.5%. This suggests that even minute amounts of Sb affect the growth dynamics substantially, and Sb‐content up to ≈3–4% yields maximum growth enhancement under the given growth conditions.…”

“…developed selective area epitaxy (SAE) of GaAs(Sb) NWs on patterned Si(111) substrates, showing that the addition of small trace amount of Sb (1–2%) leads to surprising enhancements in the axial NW growth. [ 28 ] This contrasts the typical growth‐limiting effect of Sb observed in VLS growth studies. [ 23–26 ] Despite these intriguing observations, no clear understanding of the obvious Sb self‐surfactant effect on the growth dynamics could yet be obtained in catalyst‐free GaAsSb NWs; for example, it remains fully unclear how the Sb self‐surfactant effect scales with Sb‐supply (content), for example, if there is a threshold Sb‐content required and whether the surfactant effect persists toward higher Sb‐content.…”

“…The information about the localized exciton dynamics, that is, the indirect type-II transitions can thus be extracted from the slow decay component of such stretched exponential tail, while the initial faster decay component represents the dynamics in the quasi-continuum states. [28,68] Hence, the slow decay component describes the long-lived transitions due to the spatial separation of e-h pairs in adjacent twin domains, evidencing that the exciton lifetimes increase with increasing Sb-flux, that is, domain segment length. To quantitatively correlate the microstructural data with the localized exciton dynamics, Figure 6b displays the mean twin-free domain length (top) and the extracted exciton lifetime (bottom) as a function of Sb-content in the GaAsSb NWs.…”