Photoelectrochemical undercut etching for fabrication of GaN microelectromechanical systems

Abstract

The authors have developed a wet, band-gap-selective, photoelectrochemical etching process capable of producing cantilever microelectromechanical systems from InGaN/GaN heterostructures. Fabricated cantilevers were successfully actuated, and resonance spectra were measured. The as-grown strain gradient in the GaN film was found to relax upon removal, resulting in upward curvature of the cantilevers. This curvature was shown to be reversible with the integration of strained InGaN layers on the top surface of the cantilever. All photoelectrochemical wet etching was conducted using a benchtop lamp-and-filter arrangement, employing GaN and InGaN films as filters.

Mechanical characterization of suspended GaN microstructures fabricated by GaN-on-patterned-silicon technique

“…1,2 In addition, the advantages in electrical, mechanical, and chemical properties, such as wide band gap, large elastic modulus, high piezoelectric, and piezoresistive coefficients, as well as chemical inertness, make GaN based material attractive for making microelectromechanical systems ͑MEMS͒, especially that for use in harsh environment. [3][4][5][6][7] Because of the lack of sizable GaN substrate, GaN based materials are commonly grown on foreign substrates with lattice mismatch and different thermal expansion coefficients. 8 Therefore, the knowledge of mechanical characteristics of GaN is essential to get high quality crackfree GaN films.…”

Dislocation- and crystallographic-dependent photoelectrochemical wet etching of gallium nitride

“…Above band-gap illumination of III-nitrides immersed in electrolytes such as KOH has resulted in substantial augmentation of etch rates in both the vertical and lateral directions, 1 allowing the formation of electronic, 2 optical, 3 and mechanical devices. 4 In general, photoenhanced wet etching of semiconductors depends on the wavelength and intensity of the illumination source, the nature of the electrolyte, and the doping and band gap of the semiconductor. In the case of III-nitride materials, the high density of threading dislocations of the material also exercises a critical influence on the etch rate and morphology of the etch process.…”

Wafer‐scale epitaxial lift‐off of GaN using bandgap‐selective photoenhanced wet etching

“…Bandgap‐selective etching of specific layers within an epitaxial structure can be accomplished by illuminating with wavelengths that absorb only within the layers of interest. This approach has been previously investigated for selective undercutting and ELO of GaN materials .…”