Polarity and dislocation dependence study of photoelectrochemical wet etching on GaN was carried out on lateral epitaxial overgrown nonpolar (11 (2) over bar0)a-GaN/(1 (1) over bar 02)r-plane sapphire substrate. This LEO nonpolar GaN sample has low dislocation density Ga- and N-faces exposed horizontally in opposite directions, which can be exposed to identical etching conditions for both polarity and dislocation dependence study. It is observed that N-face GaN is essentially much chemically active than Ga-face GaN, which shows the hexagonal pyramids with {10 (1) over bar(1) over bar} facets on the etched N face. No obvious etching was observed on Ga face in the same etch condition. As for dislocation dependence, the "wing" (low dislocation density) region was etched faster than the "window" (high dislocation density) region. Smooth etched surfaces were formed with the ((1) over bar(1) over bar2 (2) over bar) facet as an etch stop plane both on Ga and N-wing region. (C) 2004 American Institute of Physics.

AlGaN/GaN current aperture vertical electron transistor (CAVET) was fabricated and optimized for band gap selective photoelectrochemical wet etching. The large polarization induced voltage offset (around 2.5-4 eV) observed in the first generation CAVET was reduced to 0.7 V in this structure by employing a delta Si doping layer buried 60 Angstrom below the In0.03Ga0.97N (60 nm thick) and bottom GaN interface to screen the polarization fields. Other sample structures were studied to achieve an aperture with both good undercut etching and a small voltage offset. It was clearly demonstrated that etch selectivity in the GaN/InGaN/GaN undercut structures was influenced by hole confinement and the chemical activity of the N-face GaN. (C) 2004 American Institute of Physics.