Backside-illuminated photoelectrochemical etching for the fabrication of deeply undercut GaN structures

A photoelectrochemical (PEC) wet-etching technique (backside-illuminated PEC) is described that utilizes the dopant or band-gap selectivity of PEC etching to fabricate deeply undercut structures. Lateral etch rates exceeding 5 μm/min have been observed, producing cantilevers in excess of 100μm in length. Dramatically different etch morphologies were noted between the frontside- and backside-illuminated etching, though dopant-dependent etch selectivities were maintained.