  We present a simple fabrication method for the realization of suspended GaAs
nanomembranes for cavity quantum optomechanics experiments. GaAs nanomembranes
with an area of 1.36 mm by 1.91 mm and a thickness of 160 nm are obtained by
using a two-step selective wet-etching technique. The frequency noise spectrum
reveals several mechanical modes in the kilohertz regime with mechanical
Q-factors up to 2,300,000 at room temperature. The measured mechanical mode
profiles agree well with a taut rectangular drumhead model. Our results show
that GaAs nanomembranes provide a promising path towards quantum optical
control of massive nanomechanical systems.
