Selective wet etching of lattice-matched AlInN–GaN heterostructures

Wet etching of AlInN–GaN epitaxial heterostructures, containing AlInN layers with InN mole fractions close to 0.17 has been studied. One molar aqueous solution of the chelating amine 1,2-diaminoethane (DAE) proved to selectively etch the AlInN layers, without the need for heating above room temperature, or photo-assistance. In experiments with a (0 0 0 1)-oriented AlInN-on-GaN bilayer, the mode of removal of the AlInN layer was predominantly lateral etching, initiated from the sidewalls of pit defects in the AlInN layer. The lateral etch rate was estimated at ∼60 nm/h. The GaN buffer layer surface was roughened concurrently with etching of the AlInN, although the DAE solution has no effect on as-grown GaN (0 0 0 1) surfaces. The roughening of the GaN surface is tentatively attributed to the charge accumulation layer expected at the AlInN–GaN heterointerface. The DAE etchant also proved effective at removing buried AlInN layers from trilayer and more complex multilayer structures, leading to the prospect of epitaxial lift-off processes, and the fabrication of three-dimensional engineered microstructures. These capabilities were demonstrated by the production of suspended microdisk structures from a GaN–AlInN–GaN trilayer, using a combination of dry and wet etching.