Vapor-liquid-solid and vapor-solid growth of self-catalyzed GaAs nanowires

Abstract

We report on the morphological and structural properties of GaAs nanowires nucleated by self-catalyzed vapor-liquid-solid processes by molecular beam epitaxy on Si-treated GaAs substrates. We found that GaAs nanowires display zincblende and/or wurtzite phase depending on the As/Ga abundance ratio at the growth front, that determines the size and supersaturation of the Ga nanoparticles at the nanowire tip. We also found that even when growth conditions lead to the disappearance of such Ga nanoparticles, preferential one-dimensional growth continues through a vapor-solid mechanism. The nanowire portions grown by vapor solid mechanism display zincblend structure

Advances in the theory of III–V nanowire growth dynamics

“…In figure 9(b), it is seen that the droplet size increase at low V/III ratios, but as the V/III is increased the expansion of the droplet slows down as growth accelerates and Ga is incorporated faster into the NW. For moderate V/III ratios, where the droplet stays in a steady-state regime, the growth rate becomes more or less linear with the As flux until it reaches a limit where the droplet gets small and eventually gets consumed [74]. The apparent linear relation between NW length and As flux at moderate V/III ratios is consistent with previous reports [75].…”

Novel TEM sample preparation using XeF2 selective Etching

“…These hexagonal features resemble very strongly the typical NW hexagonal crosssection shown in Fig. 2(b) and those reported elsewhere [4,5] . Figure 4 displays a greater magnification of the hexagonal features.…”

“…Figure 2 shows a low resolution SEM micrograph of the as grown NW substrate (Fig.2a) while a high density epitaxially grown GaAs NWs with a hexagonal cross-section are visible on the surface (Fig.2b). The inset in Fig.2b clearly shows the Ga assistant droplet, confirming a vapour-liquid-solid growth mechanism [4,5] . The disappearance of the reference Si sample suggests that silicon was entirely removed from the NWs (Fig.3a).…”

“…Prior to the growth, the Si substrate was dipped in 10% aqueous HF, rinsed in deionized water then dried with a nitrogen (N2) flow, to remove the native oxide. The details of the growth protocol are discussed elsewhere [4] . In essence, the substrates underwent a 10 second Ga deposition to assist with the formation of metal droplets prior to growing the NWs at 630 °C for 60 minutes in an As/Ga ratio of 0.4.…”

Droplet destabilization during Bi catalyzed vapor-liquuid-solid growth of GaAs

“…However, these methods require an additional mask, such as a perforated oxide layer, in order to produce quality vertical nanowires. [16][17][18][19][20][21] Bi is a strong alternative as a catalyst for III-V compound semiconductors. Bi has already been shown to catalyze growth of SnS 2 , GaAs, InP, GaP, and InAs nanowires in solution using nanocrystalline Bi particles.…”