Investigation of Interface, Defects, and Growth of GaSb/Si Heteroepitaxial Films using Aberration-Corrected Scanning Transmission Electron Microscopy

Abstract

<p>Heteroepitaxial films of group III-antimonide-based semiconductor compounds on Si are amongst the most appealing candidates for solar applications because of the well-established Si platform and also for offering band-gap energies beyond the silicon road map. Nonetheless, high lattice mismatch between GaSb and Si as well as ambiguous nucleation of GaSb on Si are major drawbacks in manufacturing of heteroepitaxial GaSb/Si films because they can generate various defects in films. Atomic-level detection of these defects and delving into their origin, orientation, distribution, propagation, and interaction with each other will therefore provide an insight into inhibiting their formation or reducing their severity. State-of-the-art aberration-corrected transmission electron microscopes have marked a new era in the investigation of interfaces and defects. With sub-angstrom electron probes in scanning transmission electron microscopes, it is possible to pinpoint the individual atomic columns at interfaces and defects.</p> <p>In this thesis, GaSb epilayers grown with molecular beam epitaxy on Si substrates were studied through aberration-corrected scanning transmission electron microscopy. The strain-relief mechanism of the epitaxial GaSb through formation of interfacial misfit dislocations was investigated and the strain distribution in the vicinity of dislocation cores as well as epitaxial layer was analyzed. The specific atomic-number dependent contrast mechanism of the high-angle annular dark-field technique enabled the unprecedented direct observation of anti-phase boundaries, the extended defects of highest interest in polar-on-nonpolar growths. This observation unraveled the ambiguity of nucleation of GaSb at interface regardless of preferential deposition of atomic species during growth procedure. The growth of GaSb at the initial stage of deposition was further investigated to understand the role of an AlSb buffer layer and growth mechanism of GaSb precisely. This investigation showed that AlSb and GaSb epilayers occur by Volmer-Weber growth mode and AlSb islands provide energetically favorable nucleation sites for GaSb film. Furthermore, taking advantage of atomic-resolution detection capability of high-angle annular dark-field in scanning transmission electron microscopy a novel mechanism of strain relief through multiple twining resulting in a lattice-registered growth of GaSb on Si(211) was elucidated. This contribution demonstrates that aberration-corrected scanning transmission electron microscopy provides profound insight into the polar-on-nonpolar growth which can be exploited to suppress the formation of structural defects.</p>