EFFECT OF GROWTH PARAMETERS ON STRUCTURAL AND OPTICAL PROPERTIES OF GALLIUM ANTIMONIDE NANOSTRUCTURES GROWN BY DROPLET EPITAXY

Abstract

This dissertation is dedicated to the intensive study of the effect of growth parameters on structural and optical properties of GaSb nanostructures grown by droplet epitaxy on GaAs (001) substrates. The nanostructure morphology is investigated by atomic force microscopy. Photoluminescence measurements are employed for the optical characterization of GaSb nanostructures buried in the GaAs matrix, and provide a lot of information about the carrier dynamics and the signatures of type-II band alignment. As a consequence of a technical limit of equipment, Sb flux intensity can be adjusted only in the low regime. Most of the obtained GaSb nanostructures are therefore ring-shaped due to the outward diffusion of Ga atoms from the Ga droplets. The tracking of the evolution of Ga droplets into GaSb quantum rings is included in this dissertation. Apart from the quantum rings, GaSb quantum dots tend to take place at high Ga amounts. The quantum ring surrounded by ring-shaped quantum dot molecules can be observed for some proper Ga deposition rate and crystallization temperature. Increasing the Ga deposition temperature results in the appearance of quantum ring-with-dot structures. Simple descriptive models are proposed to elucidate the formation mechanisms of such nanostructures. Strain caused by a lattice mismatch between GaSb and GaAs also plays a role in the shape derivation. For droplet epitaxy, the GaSb nanostructures are often formed along with a GaSb layer which acts as a carrier transfer channel between the nanostructures and thus degrades the hole confinement ability of the GaSb nanostructures. However, the growth of GaSb quantum rings without the GaSb layer is demonstrated by applying very low crystallization temperature.