From the nucleation of wiggling Au nanostructures to the dome-shaped Au droplets on GaAs (111)A, (110), (100), and (111)B.

Ming-Yu Li,Mao Sui,Eun-Soo Kim,Jihoon Lee

doi:10.1186/1556-276x-9-113

Abstract

In this paper, the systematic evolution process of self-assembled Au droplets is successfully demonstrated on GaAs (111)A, (110), (100), and (111)B. On various GaAs substrates, self-assembled Au clusters begin to nucleate at around 300°C, and then, they develop into wiggly Au nanostructures at 350°C. Between 400°C and 550°C, the self-assembled dome-shaped Au droplets with fine uniformity are fabricated with various sizes and densities based on the Volmer-Weber growth mode. Depending on the annealing temperature, the size including the average height and lateral diameter and the density of Au droplets show the opposite trend of increased size with correspondingly decreased density as a function of the annealing temperature due to the difference in the diffusion length of adatoms at varied activation energy. Under an identical growth condition, depending on the surface index, the size and density of Au droplets show a clear distinction, observed throughout the temperature range. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM) images, cross-sectional line profiles, and Fourier filter transform (FFT) power spectra as well as the summary plots of the size and density.

Highlights

Due to their increased cross-section and surface area as well as the size-dependent quantum confinement, semiconductor nanowires (NWs) have been successfully utilized in numerous device applications such as solar cells, LEDs, and FETs [1,2,3,4,5,6,7,8]
After the Au deposition before annealing, the surface showed a quite smooth topography as clearly observed by the atomic force microscopy (AFM) image in Figure 2a, and the line profile in Figure 2 (a-1) and the corresponding Fourier filter transform (FFT) spectrum in Figure 2 (a-2) showed a quite broad round pattern due to the narrow random surface modulation
With the increased Ta on GaAs (111)A, apparent transitions of surface morphologies at each Ta were clearly observed and the height modulation was gradually enlarged as a function of Ta; a sharp transition was observed at 350°C with a surface modulation of approximately ±10 nm due to the increased diffusion of Au adatoms induced by the enhanced thermal energy

Summary

Introduction

Due to their increased cross-section and surface area as well as the size-dependent quantum confinement, semiconductor nanowires (NWs) have been successfully utilized in numerous device applications such as solar cells, LEDs, and FETs [1,2,3,4,5,6,7,8]. In the VLS growth, Au droplets serve as catalysts, and regardless of the materials and substrates utilized, the vapor-phase atoms could diffuse into the liquid-phase Au droplets [17,18]; from the supersaturated Au alloy droplets, the crystallization of NWs can occur at the liquid–solid interface due to the higher sticking probability at the interface [19,20,21,22,23]. The diameter, size, configuration, and even the density of NWs can innately be determined by those of the Au catalysts, and the control of Au droplets is an essential step for the successful fabrication of the desired NWs. to date, the systematic studies on the evolution of Au droplets on various GaAs substrates are deficient, and in this paper, the detailed study on the evolution of the self-assembled Au droplets on GaAs (111)A, (110), (100), and (111)B is investigated.

Methods

Results

Conclusion