Impact of the Ga flux incidence angle on the growth kinetics of self-assisted GaAs nanowires on Si(111)

Abstract

In this work we show that the incidence angle of group-III elements fluxes plays a significant role on the diffusion-controlled growth of III-V nanowires (NWs) by molecular beam epitaxy (MBE). We present a thorough experimental study on the self-assisted growth of GaAs NWs by using a MBE reactor equipped with two Ga cells located at different incidence angles with respect to the surface normal of the substrate, so as to ascertain the impact of such a parameter on the NW growth kinetics. The as-obtained results show a dramatic influence of the Ga flux incidence angle on the NW length and diameter, as well as on the shape and size of the Ga droplets acting as catalysts. In order to interpret the results we developed a semi-empirical analytic model inspired by those already developed for MBE-grown Au-catalyzed GaAs NWs. Numerical simulations performed with the model allow to reproduce thoroughly the experimental results (in terms of NW length and diameter and of droplet size and wetting angle), putting 1 arXiv:1907.03226v1 [cond-mat.mes-hall] 7 Jul 2019 in evidence that under formally the same experimental conditions the incidence angle of the Ga flux is a key parameter which can drastically affect the growth kinetics of the NWs grown by MBE. IntroductionGaAs nanowires (NWs) are one of the most promising materials for the integration of III-V semiconductors on Si, since they can be grown by molecular beam epitaxy (MBE) on Si substrates via self-assisted vapor-liquid-solid (VLS) mechanism 1-8 preventing the use of Au catalyst which would jeopardize the electronic and optoelectronic properties of these semiconductors, forming deep-level states in both of them. 9-14 When it comes to MBE, both Au-catalyzed and self-assisted growths of NWs are diffusion-controlled processes. Many theoretical and experimental studies were carried out to understand the growth mechanisms and to identify the parameters influencing the NW structure and the growth kinetics. 2,3,7,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] First works have shown that the catalyst droplet volume or shape 15,16,18,27,31 and, more recently, that the droplet wetting angle 20,22,24 do control the NW crystal structure through the location of the nucleation site. Moreover, the volume of the catalyst droplet controls the kinetics of the axial growth through the related capture surface, 25,26,28 and in particular, through the capture area for As in the case of self-assisted GaAs NWs. 18,22 Concerning the NW growth kinetics, the growth models developed so far take into account the Ga flux incidence angle 17,18,22,23,25,26,28,30 but do not demonstrate its influence. In particular, the model of Glas et al 17 for self-assisted GaAs NWs was based on the assumption that the Ga flux adopted is always high enough to supply the Ga droplet, therefore neglecting to consider the influence of the incidence angle of the Ga flux on the amount of

Phase-Pure Wurtzite GaAs Nanowires Grown by Self-Catalyzed Selective Area Molecular Beam Epitaxy for Advanced Laser Devices and Quantum Disks

“…We attribute this double-stage NW length evolution to the interplay of competing main contribution pathways for Ga atoms feeding the catalyst droplet. 35 Once the NW length exceeds the diffusion length of Ga on the side facets, the amount of Ga diffusing from the SiO 2 surface over the side facets to the droplet vanishes. Simultaneously, the contribution from direct impingement of Ga onto the NW side facets and subsequent diffusion to the droplet is enhanced because the area of the side facets scales with the increasing length of the NW.…”

Crystal phase engineering of self-catalyzed GaAs nanowires using a RHEED diagram

“…By extending the semi-empirical growth model for Au-catalyzed GaAs 25,32,42 and InAs 43 NWs, we proposed in Vettori et al 44 a model for self-catalyzed GaAs NWs able to account for the droplet evolution as a function of (a) the direct Ga and As fluxes and (b) the Ga atoms entering the droplet by diffusion on the SiO2-terminated Si substrate (for short NWs) and on the NW facets (more details can be found in the Supplementary Information section). Motivated by the droplet stability at a solid angle, an original feature of the model exposed by Vettori et al 44 . is the existence of an upper-limit wetting angle for the droplet.…”

Insights into the Arsenic Shell Decapping Mechanisms in As/GaAs Nanowires by X-ray and Electron Microscopy

“…After rinsing, the substrates were outgassed at 200 °C under UHV for a few minutes and then transferred into the MBE chamber. The MBE chamber was equipped with a Ga Knudsen cell with an incident angle of 27.9° and an As valve cracked cell. GaAs NWs were grown using the vapor–liquid–solid (VLS) mechanism with Ga droplets as catalysts. , Because no native silicon oxides were removed beforehand, the Si substrate temperature was increased to 530 °C, and one monolayer (ML) of Ga was deposited on the substrate at an equivalent GaAs two-dimensional growth rate of 0.50 ML/s. , Then, the substrate temperature was increased to 610 °C to begin the growth of GaAs NWs by providing Ga and As fluxes simultaneously.…”