Thesis presented December 10, 2004

Abstract:
In this thesis we present the structural characterization of GaN/AIN quantum wells (QWs) and quantum dots (QDs) grown by plasma assisted molecular beam epitaxy. The technique we use is the transmission electron microscopy in (i) high resolution, (ii) energy filtered, (Hi) conventional and (iv) convergent beam modes. The quantitative analysis of our nanostructures is realized using a projection method and the geometric phase analysis. In order to obtain the most accurate results those methods are optimized and specific experimental conditions, like off-axis HRTEM images, are applied. A comparison study between a Ga-face and a N-face GaN/AIN superlattice (SL) is presented and the higher structural quality (the Ga-face SL is proven: abrupt and uniform interfaces, absence of inversion domain boundaries and partially strained QWs. We also analyze the effects of AIN overgrowth on the structural quality of GaN nanostructures. We show that the overgrowth process implies a thinning of the GaN QWs and an isotropic reduction of the GaN QDs size. The phenomenon is attributed to an exchange mechanism between AI atoms from the cap layer and Ga atoms in the nanostructures. We investigate the strain distribution in a GaN/AIN QD superlattice. Using HRTEM, theoretical calculations and X-ray diffraction experiments we demonstrate that the vertical alignment of the QDs is due to a modulation of the strain state of the AIN layers. Finally, we examine the polytype conversion of a GaN film from N-face wurtzite to zinc-blende structure due to Mg high doping.

Keywords:
Electron microscopy, molecular beam epitaxy, GaN/AIN, quantum dot

On-line thesis. ​