LETTER pubs.acs.org/NanoLett Formation of High Aspect Ratio GaAs Nanostructures with Metal-Assisted Chemical Etching

’High aspect ratio semiconductor nanostructures are becoming more prevalent in many applications including solar cells, light emitting diodes (LEDs), field effect transistors (FETs), thermo-electric devices, and sensing.15 These nanostructures can be formed from either the bottom up by growth or the top-down by etching. For top-downmethods, one of the most used methods is reactive ion etching of a patterned substrate.6 However, this can result in extensive damage to the crystal structure and surface morphology because of the high-energy ions involved. For silicon, such surface damage can be repaired by thermal anneal-ing. However, for compound semiconductors, such as GaAs, thermal repair is not completely effective mainly because of the difficulty of maintaining stoichiometry.7,8 One top-down etching method, which is becoming increasingly more favorable, is metal-assisted chemical etching (MacEtch), a simple directional we