In Situ Monitoring of MBE Growth of a Single Self-Catalyzed GaAs Nanowire by X-ray Diffraction

Abstract

Self-catalyzed GaAs nanowires (NWs) on Si substrates are one of the superior candidates for future electronics and optoelectronics integrated with a silicon electronic platform. To bring the NWs from laboratories to industry, it is essential to further develop their basic science and engineering. In situ growth monitoring plays an important role in understanding the fundamental growth mechanisms influencing the resulting properties of NWs. We report on monitoring the growth of an individual self-catalyzed GaAs NW on a patterned Si substrate by molecular beam epitaxy utilizing a micro X-ray diffraction (XRD) setup. For the first time, the full growth run of a single NW was monitored by XRD over a time span of about 1 h. It was found that the NW growth follows two stages. In the first stage, the NW axial growth is dominant while the NW oscillates within 1° tilt angle with respect to the substrate normal. In the second stage, the NW starts to grow radially maintaining a stable orientation. These findings are explained within a dedicated model. From a technical point of view, our results demonstrate the feasibility of in situ growth experiments with NWs/nanoparticles using synchrotron radiation.

Theory of MBE Growth of Nanowires on Adsorbing Substrates: The Role of the Shadowing Effect on the Diffusion Transport

“…For self-catalyzed III-V NWs, the axial growth rate is determined by the incoming flux of group V atoms and their desorption from the droplet [ 10 , 37 ]. However, the total balance of group III atoms is still relevant [ 33 , 35 , 38 , 39 ]. I will assume the absence of desorption of group III atoms from the substrate surface, NW sidewalls and catalyst droplets resting on the tops of VLS NWs, as discussed above.…”

“…I will assume the absence of desorption of group III atoms from the substrate surface, NW sidewalls and catalyst droplets resting on the tops of VLS NWs, as discussed above. In the case of an adsorbing substrate, the diffusive growth species are collected by the droplet, NW sidewalls and also from a feeding ring of width on the substrate surface [ 18 , 21 , 23 , 26 , 29 , 38 ]. This can be called the diffusion length of group III adatoms, which describe the temperature-dependent surface mobility of these adatoms on a given substrate surface.…”

“…This can be called the diffusion length of group III adatoms, which describe the temperature-dependent surface mobility of these adatoms on a given substrate surface. Outside these rings surrounding the NWs, the deposited material agglomerates in the form of parasitic islands (on masked surfaces [ 24 , 38 ]) or a quasi-2D layer (on unpatterned surfaces [ 16 , 18 , 23 ]). The NW shape is assumed cylindrical, with the length above the substrate surface and uniform radius from base to top.…”

“…[ 23 ]. Self-catalyzed VLS III-V NWs [ 33 , 37 , 38 , 39 , 42 , 43 ] often grow radially from the very beginning. This feature is due to the fact that a catalyst droplet serves as a non-stationary reservoir of group III atoms and can either swell or shrink depending on the V/III flux ratio and surface diffusivity of group III adatoms [ 42 , 43 ].…”

“…Growth kinetics of NWs can be understood deeper through in situ [ 38 ] or ex situ [ 21 , 31 , 33 ] studies of the morphological evolution with the growth time or deposition thickness. GaAs NWs of Ref.…”