Ar/Cl$_{2}$ etching of GaAs optomechanical microdisks fabricated with positive electroresist

A method to fabricate GaAs microcavities using only a soft mask with an electrolithographic pattern in an inductively coupled plasma etching is presented. A careful characterization of the fabrication process pinpointing the main routes for a smooth device sidewall is discussed. Using the final recipe, optomechanical microdisk resonators are fabricated. The results show a very high optical quality factors of $Q_\text{opt}>2\times 10^{5}$, among the largest already reported for dry-etching devices. The final devices are also shown to present high mechanical quality factors and an optomechanical vacuum coupling constant of $g_{0}=2\pi\times 13.6$ kHz enabling self-sustainable mechanical oscillations for an optical input power above $1$ mW.