Effects of Doping and Orientation on Photoelectrochemically Etched Features in n-GaAs

Photoelectrochemical etching of high aspect ratio mask-defined grooves in (10_0) n-GaAs is shown to be dependent on both crystal lographic orientation and doping level. Structures etched along the [011] direction produced V-grooves, show-ing that the (111)Ga surface is a stop plane with respect o ox idat ion by photogenerated holes. Other or ientat ions etch more isotropically. In all cases, undercutt ing of the mask is associated with lateral diffusion of holes due to slow kinetics of consumpt ion by the interfacial reaction. This effect is minimized in highly doped crystals, where high quality vertical wal led gratings can be produced using visible l ight with aspect ratios of> 10:1. Photoe lec t rochemica l e tch ing of semiconductors has been a subject of cons iderable recent interest for the fab-r icat ion of so l id-state optoe lec t ron ic e lements such as d i f f ract ion grat ings for d i s t r ibuted feedback lasers (1) and integra l lenses for l ight emi t t ing d iodes (2). There have also been several accounts of e tch ing deep struc-tures, par t icu lar ly via holes, us ing a focused u l t rav io let laser on I I I-V crystals s imply immersed in etch ing elec