Effects of doping and orientation on photoelectrochemically etched features in n-GaAs

Photoelectrochemical etching of high aspect ratio mask-defined grooves in (100)n-GaAs is shown to be dependent on both crystallographic orientation and doping level. Structures etched along the (011) direction produced V grooves, showing that the (111)Ga surface is a stop plane with respect to oxidation by photogenerated holes. Other orientations etch more isotropically. In all cases, undercutting of the mask is associated with lateral diffusion of holes due to slow kinetics of consumption by the interfacial reaction. This effect is minimized in highly doped crystals, where high quality vertical walled gratings can be produced using visible light with aspect ratios of >10:1.