Fully unstrained GaN on sacrificial AlN layers by nano‐heteroepitaxy

Abstract

AbstractUsually, the fabrication of microelectromechanical systems (MEMS) requires unstrained or tensile strained active layers on a selectively removable sacrificial layer, since compressive strain causes instabilities due to buckling effects. For group III‐nitride based MEMS, AlN is a promising material for sacrificial layers since it can be epitaxially overgrown and etched selectively to GaN. However, due to the larger lattice constants GaN is growing compressively strained on AlN. Nanoheteroepitaxy opens a way to yield fully unstrained, high quality epitaxial GaN layers on nanocrystalline AlN thin film by means of a 3D strain relaxation mechanism. For this purpose sputtered nanocrystalline AlN films were overgrown with single crystalline GaN and AlGaN/GaN layers by metalorganic chemical vapor deposition. The high quality of the layers is proven by an atomically flat surface and a 2D electron gas at the interface of the AlGaN/GaN heterostructure (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)