Professor Robert Taylor

Abstract:

The great success that GaN-based structures have enjoyed in implementing efficient optoelectronic devices has fostered a rapidly expanding interest amongst researchers aimed at understanding their underlying physics. There has been an active debate on the mechanisms that give rise to efficient luminescence in these materials. In this paper we approach these questions through optical studies of single InGaN/GaN quantum dots in the context of the available experimental and theoretical understanding of InGaN structures in general, and of three-dimensional localization in this material in particular. We will also show how it is possible to exploit the various unique properties that nitride-based materials offer, such as the strong inbuilt electric field, in a controlled manner. Such control may in the future prove essential for the implementation of single quantum dot devices in applications such as quantum information processing. We also show how nonlinear spectroscopy provides an invaluable tool in suppressing background luminescence effects inherent in this material.

Abstract:

Photoluminescence (PL) properties of a single nanorod containing multiple GaN quantum disks separated by AlGaN potential barriers are investigated using micro-PL spectroscopy. Previous studies reported ensemble spectra from many nanorods. The PL spectra show different features depending on the region of the nanorod excited by the laser, including a sharp feature originating from the quantum disk region. The distinct differences between the PL from the different regions are discussed. The results imply that excitons are strongly confined in the quantum disks, and the authors suggest that small quantum disks can be regarded as quantum dots having a discrete density of states. © 2007 American Institute of Physics.

Abstract:

The surface morphologies of AlN and GaN on Si(111) and Si(100) were studied using atomic force microscopy. The AlN buffer layer was deposited using RF sputtering for 30 minutes on Si(111) and Si(100) substrates, and then the specimens were annealed at 850 °C, 950 °C and 1050 °C for 60 minutes in an NH3 atmosphere. It was found that the grains of AlN became larger by increasing the annealing temperature. GaN was grown on AlN/Si(111) and AlN/Si(100) substrates by using a hydride vapor phase epitaxy technique. The surface of GaN grown on the AlN/Si substrate showed thick- thread and fine-thread patterns. The microstructure of GaN grown on the buffer-GaN/Al 2O3 had a step-flow pattern. These phenomena could be explained by a lattice mismatch and the growth temperature. A power spectral density analysis was performed on the GaN surfaces and the results were compared with the experimental data.