PAMBE growth of (1 1 (2)over-bar 2)-oriented GaN/AlN nanostructures on m-sapphire

We report on the plasma-assisted molecular-beam epitaxial growth of (11 (2) over bar 2)-oriented GaN/AlN nanostructures on (1 (1) over bar 0 0) m-plane sapphire. Moderate N-rich conditions enable to synthesize AlN(1 1 (2) over bar 2) directly on m-sapphire, with in-plane epitaxial relationships [1 1 (2) over bar (3) over bar](AlN)parallel to[0 0 1 1](sapphire) and [1 (1) over bar 0 0](AlN)parallel to[1 1 (2) over bar 0](sapphire). In the case of GaN, a Ga-excess of one monolayer is necessary to achieve two-dimensional growth of GaN(1122). Applying these growth conditions, we demonstrate the synthesis of (1 1 (2) over bar 2)-oriented GaN/AlN quantum well structures, showing a strong reduction of the internal electric field. By interrupting the growth under vacuum after the deposition of few monolayers of GaN under slightly Ga-rich conditions, we also demonstrate the feasibility of quantum dot structures with this orientation. (C) 2008 Elsevier Ltd. All rights reserved.