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An electrochemical etching based on oxalic acid was developed for use in the chemical lift-off of GaN epitaxial structures. It was shown that only the Si-doped n-GaN layer was etched away, while the p-type and undoped GaN layers were not etched at all. The etch rate and the remaining structure were analyzed for various doping concentrations and etching voltages. A lateral etch rate of 12 μm/min was achieved under 60 V for n-type doping concentration of 8×1018 cm−3. This doping selective etching was used to lift-off a GaN epitaxial layer patterned into 300×300 μm2 squares.

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Electrochemical etching having large selectivity based on the conductivity of n-type GaN was investigated to demonstrate the feasibility of novel optical and microelectromechanical system devices. The electrochemical etching exhibited two regimes with different etching characteristics, i.e., nanoporous and electropolishing, depending on the doping concentration and applied voltage. For photonic applications, GaN microdisks and distributed Bragg reflectors were fabricated where optical index contrast can be achieved by selective etching or nanoporous formation of GaN. Stimulated emission of GaN microdisk was observed under pulsed optical pumping. In addition, a GaN cantilever was formed and its resonance frequency was measured at $120 kHz.

A high-efficiency GaN-based thin film piezoelectric energy harvester was demonstrated by suppressed screening of a piezoelectric field with the aid of a p–n diode junction.