Defects in GaN layers grown by hydride vapor-phase epitaxy have been invest
igated by photoelectrochemical (PEC) etching, and by wet etching in hot H3P
O4 acid and molten potassium hydroxide (KOH). Threading vertical wires (i.e
., whiskers) and hexagonal-shaped etch pits are formed on the etched sample
surfaces by PEC and wet etching, respectively. Using atomic-force microsco
py, we find the density of "whisker-like" features to be 2x10(9) cm(-2), th
e same value found for the etch-pit density on samples etched with both H3P
O4 and molten KOH. This value is comparable to the dislocation density obta
ined in similar samples with tunneling electron microscopy, and is also con
sistent with the results of Youtsey and co-workers [Appl. Phys. Lett. 73, 7
97 (1998); 74, 3537 (1999)]. (C) 2000 American Institute of Physics. [S0003
-6951(00)05348-1].