Alkaline treatment of Al-rich porous sacrificial Al80Ga20N layers

III-nitride semiconductors have a tunable, direct bandgaps that cover the spectrum from deep UV for AlN, to near IR for InN. By creating alloys out of these materials it is possible to cover large part of electromagnetic spectrum with tunable bandgap, where concentration of each material directly impacts the bandgap. Alloys such as aluminium gallium nitride (AlxGa(1−x)N) be applicable for deep-UV optoelectronic devices used in communication, nanofabrication, medicine, sterilization and sanita- tion. High performance devices such as vertical-cavity surface-emitting lasers (VC- SELs), requires high reflectivity mirrors, best of which can be achieved by substrate removal via underetching of sacrificial layer and sputtering. Electrochemical etching is one of methods that can be used for underetching however its efficiency decreases as the Al concentration increases. This method can be improved by introducing a UV illumination source, but it still is not enough as with higher Al concentration the sacrificial layer because porosified rather than completely dissolved. This work investigates an enhanced method consisting of two-step PECE for 80%-Al content AlGaN sacrificial layer. The method combines an initial PECE in combi- nation of 0.3 M nitric acid and 0.3 M phosphoric acid during which sacrificial layer porisifies, followed by a photoassisted alkaline treatment using various concentra- tions of potassium hydroxide (KOH) to dissolve the porous walls and allow mem- brane exfoliation. The surface morphology, pore structures, and exfoliation behavior were characterized using optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Initial exploratory phases revealed that exfoliated membranes were highly delicate and tending to fully dissolve during neutralization steps or when exposed to too high alkaline concentrations. KOH concentration of above 1 mM result in fast and uncontrollable vertical etching that destroyed the exfoliated membrane. While we did not find optimal parameters for full sacrificial layer removal, lower concentra- tions of KOH in range of about 0.1 mM to 1 mM resulted in successful membrane exfoliation proving that this method definitely can be improved with further studies.