The underlying physics in the formation of self-assembled (indium,gallium)arsenic nanostructures
Abstract
The main focus of this dissertation is in the physics that underline the fabrication and characterization of self-assembled III-V compound semiconductor nanostructures. Using the (100) GaAs substrates as a reference, we used droplet epitaxy to present a study on the formation of Ga droplets on (311)A and (511)A GaAs substrates in which both substrate temperature and the amount of Ga supplied is found to affect the droplet density size, and shape. We offer a physical explanation of the droplets properties based on thermodynamics and the anisotropy of the high index surfaces. The evolution between lattice-matched GaAs/Al0.3Ga0.7 As single and double ring-like nanostructures is also studied, with an emphasis on the construction and destruction of the observed outer ring. Using droplet epitaxy, this was achieved by directly controlling the Ga surface diffusion on GaAs (100) by varying the substrate temperature, amount of Ga, and the As4 flux. The role of the size of GaAs/Al0.3Ga 0.7As ring-like nanostructures on their optical properties was also investigated. We also made a direct comparison between the photoluminescence (PL) from non-oxidized and oxidized uncapped InAs/GaAs quantum dots (QDs) and we report on a drastic change in the energy position and intensity of the PL as the QDs get closer to the top surface of the structure. Based on these observations, we offer a physical explanation for our observation and for the discrepancies between previously reported results. In addition, we propose a combination of properties to control ordering of QDs on a GaAs surface using the surface natural anisotropy for (100), surface steps on high index GaAs substrates, and the Arsenic background. Ordered QDs with low indium composition on a GaAs (001), (311)B and (511)B was obtained for one and multilayered structures. Finally, using Stranski-Krastanov growth procedure we have fabricated quantum rings (QRs) by partially covering InAs QDs with 4 nm of GaAs layer under AS2 flux. Structural and optical properties of the fabricated rings display good QR homogeneity. Bilayers QRs samples were also prepared with different spacer thickness and a strong coupling between the QRs is produced.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 2007
- Bibcode:
- 2007PhDT........40A