Ordered Al _xGa_{1- x}As Nanopillar Arrays via Inverse Metal-Assisted Chemical Etching

The ternary III-V semiconductor compound, Al _xGa_{1 -x}As, 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 _xGa_{1 -x}As 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 _xGa_{1 -x}As 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 Al_0.55Ga_0.45As 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.