Dislocation density in GaN determined by photoelectrochemical and hot-wet etching

Defects in GaN layers grown by hydride vapor-phase epitaxy have been investigated by photoelectrochemical (PEC) etching, and by wet etching in hot H3PO4 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 microscopy, we find the density of "whisker-like" features to be 2x10(9) cm(-2), the same value found for the etch-pit density on samples etched with both H3PO4 and molten KOH. This value is comparable to the dislocation density obtained in similar samples with tunneling electron microscopy, and is also consistent with the results of Youtsey and co-workers [Appl. Phys. Lett. 73, 797 (1998); 74, 3537 (1999)]. (C) 2000 American Institute of Physics. [S0003-6951(00)05348-1].