Inverse metal-assisted chemical etching produces smooth high aspect ratio InP nanostructures.

Creating high aspect ratio (AR) nanostructures by top-down fabrication without surface damage remains challenging for III-V semiconductors. Here, we demonstrate uniform, array-based InP nanostructures with lateral dimensions as small as sub-20 nm and AR > 35 using inverse metal-assisted chemical etching (I-MacEtch) in hydrogen peroxide (H2O2) and sulfuric acid (H2SO4), a purely solution-based yet anisotropic etching method. The mechanism of I-MacEtch, in contrast to regular MacEtch, is explored through surface characterization. Unique to I-MacEtch, the sidewall etching profile is remarkably smooth, independent of metal pattern edge roughness. The capability of this simple method to create various InP nanostructures, including high AR fins, can potentially enable the aggressive scaling of InP based transistors and optoelectronic devices with better performance and at lower cost than conventional etching methods.

Ordered Al xGa1- xAs Nanopillar Arrays via Inverse Metal-Assisted Chemical Etching.

The ternary III-V semiconductor compound, Al xGa1 -xAs, is an important material that serves a central role within a variety of nanoelectronic, optoelectronic, and photovoltaic devices. With all of its uses, the material itself poses a host of fabrication difficulties stemming from conventional top-down processing, including standard wet-chemical etching and reactive-ion etching (RIE). Metal-assisted chemical etching (MacEtch) techniques provide low-cost and benchtop methods that combine many of the advantages of RIE and wet-chemical etching, without being hindered by many of their disadvantages. Here, inverse-progression MacEtch (I-MacEtch) of Au-patterned Al xGa1 -xAs is demonstrated for the first time and is exploited for the generation of vertical and ordered nanopillar arrays. The etching solution employed here consists of citric acid (C6H8O7) and hydrogen peroxide (H2O2). The I-MacEtch evolution is tracked in time for Al xGa1 -xAs samples with compositions defined by x = 0.55, x = 0.60, and x = 0.70. The vertical and lateral etch rates (VER and LER, respectively) are shown to be tunable with Al fraction and temperature of the etching solution, based on modification of catalytically injected hole distributions. Control over the VER/LER ratio is demonstrated by tailoring etch conditions for single-step fabrication of ordered AlGaAs nanopillar arrays with predefined aspect ratios. Maximum VER and LER values of ∼40 nm/min and ∼105 nm/min, respectively, are measured for Al0.55Ga0.45As at a process temperature of 65 °C. The I-MacEtch nanofabrication methodology outlined in this study may be utilized for the processing of many devices, including high electron mobility transistors, distributed Bragg reflectors, lasers, light-emitting diodes, and multijunction solar cells containing AlGaAs components.

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.