Fabrication of Suspended III-V Nanofoils by Inverse Metal-Assisted Chemical Etching of In0.49Ga0.51P/GaAs Heteroepitaxial Films.

Metal-assisted chemical etching (MacEtch) has been established as a low-cost, benchtop, and versatile method for large-scale fabrication of semiconductor nanostructures and has been heralded as an alternative to conventional top-down approaches such as reactive-ion etching. However, extension of this technique to ternary III-V compound semiconductor alloys and heteroepitaxial systems has remained relatively unexplored. Here, Au-assisted and inverse-progression MacEtch (I-MacEtch) of the heteroepitaxial In0.49Ga0.51P/GaAs material system is demonstrated, along with a method for fabricating suspended InGaP nanofoils of tunable thickness in solutions of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). A comparison between Au- and Cr-patterned samples is used to demonstrate the catalytic role of Au in the observed etching behavior. Vertical etch rates for nominally undoped, p-type, and n-type InGaP are determined to be ∼9.7, ∼8.7, and ∼8.8 nm/min, respectively. The evolution of I-MacEtch in the InGaP/GaAs system is tracked, leading to the formation of nanocavities located at the center of off-metal windows. Upon nanocavity formation, additional localized mass-transport pathways to the underlying GaAs substrate permit its rapid dissolution. Differential etch rates between the epilayer and substrate are exploited in the fabrication of InGaP nanofoils that are suspended over micro-trenches formed in the GaAs substrate. A model is provided for the observed I-MacEtch mechanism, based on an overlap of neighboring injected hole distribution profiles. The nanofabrication methodology shown here can be applied to various heteroepitaxial III-V systems and can directly impact the conventional processing of device applications in photonics, optoelectronics, photovoltaics, and nanoelectronics.