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

Abstract

Free-standing III-V semiconductor nanowires (NW) are very attractive materials due to their unique physical properties Vapor-liquid-solid (VLS) growth is the mainstream method in realizing advanced semiconductor nanowires (NWs), as widely applied to many III-V compounds. It is exclusively explored also for antimony (Sb) compounds, such as the relevant GaAsSb-based NW materials, although morphological inhomogeneities, phase segregation, and limitations in the supersaturation due to Sb strongly inhibit their growth dynamics. Fundamental advances are now reported here via entirely catalyst-free GaAsSb NWs, where particularly the Sb-mediated effects on the NW growth dynamics and physical properties are investigated in this novel growth regime. Remarkably, depending on GaAsSb composition and nature of the growth surface, both surfactant and anti-surfactant action is found, as seen by transitions between growth acceleration and deceleration characteristics. For threshold Sb-contents up to 3-4%, adatom diffusion lengths are increased ≈sevenfold compared to Sb-free GaAs NWs, evidencing the significant surfactant effect. Furthermore, microstructural analysis reveals unique Sb-mediated transitions in compositional structure, as well as substantial reduction in twin defect density, ≈tenfold over only small compositional range (1.5-6% Sb), exhibiting much larger dynamics as found in VLS-type GaAsSb NWs. The effect of such extended twin-free domains is corroborated by ≈threefold increases in exciton lifetime (≈4.5 ns) due to enlarged electron-hole pair separation in these phase-pure NWs.

Axial Growth Characteristics of Optically Active InGaAs Nanowire Heterostructures for Integrated Nanophotonic Devices

“…To induce site-selective NW growth, the SiO 2 mask layer was prepatterned using electron beam lithography, reactive ion etching, and wet chemical etching with buffered hydrofluoric acid. ,− This process involved creating periodically arranged circular hole-openings with varying nominal diameters of d 0 = 30–120 nm and a pitch ( p ) of 500 nm (unless otherwise noted). Using these prepatterned openings, the growth of noncatalytic vertical NWs with a high yield was initiated by following the procedures reported in our previous work. ,, First, GaAsSb NWs were grown for 60 min at a temperature of 630 °C, using a Ga flux of 0.35 Å/s, an As BEP (beam equivalent pressure) of 5.5 × 10 –5 mbar, and a Sb BEP of 3 × 10 –7 mbar, respectively. The GaAsSb NWs served as a stem for the subsequent axial heterostructure, which contained only a small Sb molar fraction (≈2–3%), given the selected Sb/As flux ratio.…”

“…For comparison, as shown in Figure 1e, a smaller hole-opening size of d 0 = 30 nm (under otherwise identical growth conditions) leads to an increased axial NW length (≈1100 ± 200 nm) and decreased diameter (≈130 ± 7 nm), a typical characteristic of the noncatalytic growth mode. 56,57,59,63,64 Likewise, the InGaAs segment also increased in axial size (≈70 nm), containing a slightly smaller amount of [In] ≈ 9.3% as compared to d 0 = 70 nm. In this example, we also observe that in thinner NWs a more pronounced facet structure is present, with extended inclined facets adjacent to the top facet, which obscure to some extent the compositional profile.…”

“…The GaAsSb NWs served as a stem for the subsequent axial heterostructure, which contained only a small Sb molar fraction (≈2−3%), given the selected Sb/As flux ratio. This low Sb content was chosen purposefully for two reasons: (i) as recently reported, small additions of Sb improve the morphological, microstructural, and optical properties of noncatalytically grown GaAs(Sb) NWs, thanks to an underlying Sb surfactant effect; 57,59 1a illustrates schematically the desired axial NW heterostructure grown by SAE on a prepatterned SiO 2 / Si(111) substrate. To view the morphology of the as-grown NW arrays, scanning electron microscopy (SEM) was conducted using a NVision 40 FIB-SEM apparatus from Carl Zeiss.…”

“…Using these prepatterned openings, the growth of noncatalytic vertical NWs with a high yield was initiated by following the procedures reported in our previous work. 56,57,59 First, GaAsSb NWs were grown for 60 min at a temperature of 630 °C, using a Ga flux of 0.35 Å/s, an As BEP (beam equivalent pressure) of 5.5 × 10 −5 mbar, and a Sb BEP of 3 × 10 −7 mbar, respectively. The GaAsSb NWs served as a stem for the subsequent axial heterostructure, which contained only a small Sb molar fraction (≈2−3%), given the selected Sb/As flux ratio.…”

“…Only a few years ago, SAE-based MBE growth of catalyst-free GaAs NWs was demonstrated for the first time, using extraordinarily high V/III ratios and specific substrate preparation schemes . Subsequent work showed that the addition of small traces of antimony (Sb ≈ 1–2%) and Si dopants helped to establish high-uniformity GaAs NW arrays with excellent aspect ratios, phase-pure crystal structures, and well-defined growth facets. − Hence, the droplet-free SAE-MBE growth of GaAs­(Sb) NWs with such pristine properties opens up great versatility for the realization of diverse axial heterostructures.…”