Figure 4.

Microscopic images of the HF undercutting of a 300 × 300 μm GaN mesa with etching time of a 3 min, b 6 min, c 9 min, d 12 min, e 15 min, and f 18 min, respectively

Zang et al. Nanoscale Research Letters 2010 5:1051-1056   doi:10.1007/s11671-010-9601-6