Record Pure Zincblende Phase in GaAs Nanowires down to 5 nm in Radius

Abstract

We report the Au catalyst-assisted synthesis of 20 μm long GaAs nanowires by the vapor-liquid-solid hydride vapor phase epitaxy (HVPE) exhibiting a polytypism-free zincblende phase for record radii lower than 15 nm down to 5 nm. HVPE makes use of GaCl gaseous growth precursors at high mass input of which fast dechlorination at the usual process temperature of 715 °C results in high planar growth rate (standard 30-40 μm/h). When it comes to the vapor-liquid-solid growth of nanowires, fast solidification at a rate higher than 100 μm/h is observed. Nanowire growth by HVPE only proceeds by introduction of precursors in the catalyst droplets from the vapor phase. This promotes almost pure axial growth leading to nanowires with a constant cylinder shape over unusual length. The question of the cubic zincblende structure observed in HVPE-grown GaAs nanowires regardless of their radius is at the heart of the paper. We demonstrate that the vapor-liquid-solid growth in our conditions takes place at high liquid chemical potential that originates from very high influxes of both As and Ga. This yields a Ga concentration systematically higher than 0.62 in the Au-Ga-As droplets. The high Ga concentration decreases the surface energy of the droplets, which disables nucleation at the triple phase line thus preventing the formation of wurtzite structure whatever the nanowire radius is.

Zeldovich Nucleation Rate, Self-Consistency Renormalization, and Crystal Phase of Au-Catalyzed GaAs Nanowires

“…the well-known results used extensively in modeling of NW growth 12,14,20,21,34 . Very importantly, the surface energy constant a is determined by the ratio of the characteristic surface energy per …”

“…In the case of semiconductor nanowires (NWs) fabricated by the metalcatalyzed vapor-liquid-solid (VLS) method 10 , the ZNR is thought to determine the probability of 2D nucleation from a supersaturated liquid alloy of a metal catalyst with the growth constituencies 2 . In this way, the ZNR controls the vertical growth rate of NWs 2,11-13 , nucleation statistics in VLS NWs [14][15][16][17] , morphology of the growth interface 18,19 and even the preferred crystal structure of Au-catalyzed III-V NWs which can be either cubic zincblende (ZB) or hexagonal wurtzite (WZ) [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] . Since most NWs grow in the so-called mononuclear mode with only one island emerging in each NW monolayer (ML) 2 , we need to consider the chain of individual nucleation events.…”

“…These results determine with high precision the driving force for 2D nucleation in VLS NWs, while the nucleation energies can be obtained within macroscopic approach 2,[11][12][13][14][15]20,21,27,30,34,37 .…”

Growth of III-V semiconductor nanowires and their heterostructures

“…Consequently, the growth direction [38] or the crystal structure [34,36,37] However, the understanding of the mechanism behind these parameters are very limited. Very recently, Gil et al [35] reported the growth of pure ZB phase GaAs NWs with diameter between 5 and 15 nm, as shown in Fig. 3a.…”

“…2). For a long time, experimentalists have shown that by changing the growth parameters, such as NW diameter [34,35], growth temperature [36], or precursor flow [37] employed during the growth, it is possible to modify the stacking order of the bilayers. Consequently, the growth direction [38] or the crystal structure [34,36,37] However, the understanding of the mechanism behind these parameters are very limited.…”