The authors report a technique for selective wet chemical etching of an AlInN sacrificial layer lattice-matched to GaN for the fabrication of air-gap photonic structures. It is used to demonstrate high quality factor (Q) microdisk cavities. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells (QWs) embedded in the GaN microdisks. Q factors of up to 3500 are obtained. The measured Qs are found to be limited by the QW absorption. Room temperature laser action is achieved for a wide spectral range (409-475 nm) with a threshold down to 166 kW/cm(2). (C) 2008 American Institute of Physics.