Free-standing Al[subscript x]Ga[subscript 1−x]As heterostructures by gas-phase etching of germanium

Abstract

We outline a facile fabrication technique for the realization of free-standing Al[subscript x]Ga[subscript 1−x]As heterostructures of arbitrary aluminum content. Utilizing xenon difluoride (XeF[subscript 2]) we rapidly and selectively remove a sacrificial germanium (Ge) underlayer in a room temperature gas-phase etching procedure. We demonstrate two possibilities for exploiting this unique process: (1) bulk micromachining of a suspended high-frequency low-dissipation micro-optomechanical resonator consisting of an epitaxial GaAs/AlAs multilayer grown on a Ge substrate and (2) epitaxial lift-off of a GaAs film via removal of an embedded Ge sacrificial layer, resulting in lateral etch rates up to 3 mm/h and a conservative selectivity of ∼ 10[superscript 6].