Professor Robert Taylor

Abstract:

We have studied the effect of annealing AIN buffer layers on the properties of subsequently grown GaN layers. The AIN buffer layer was deposited on a Si(111) substrate by using RF sputtering, and different samples were then annealed at temperatures of 700 degrees C, 800 degrees C, and 900 degrees C. Thick GaN was grown using a hydride vapor phase epitaxy (HVPE) system for 1 hour at 1050 degrees C with the resultant thickness being 150 mu m. The morphologies of the AIN and the GaN layers were observed by using both atomic force microscopy (AFM) and scanning electron microscopy (SEM). The surface roughness and grain size of the AIN buffer layer was increased by raising the annealing temperature; this was accompanied by an improvement in the two-dimensional lateral growth of the GaN layer. X-Ray diffraction (XRD) patterns showed the typical results expected for GaN (0002) and (0004) faces, revealing a highly preferred orientation of the GaN(0001) surface. However, a residual compressive stress was observed between the GaN and the Si substrate, independent of the annealing treatment of the buffer layer.

Abstract:

We present a study of the time-integrated and time-resolved photoluminescence properties of single-InGaN/GaN quantum dots (QDs) using two-photon spectroscopy. Two samples containing QDs produced by different growth techniques are examined. We find that two-photon excitation results in the suppression of the emission from the underlying quantum well to which the QDs are coupled and yet relatively strong QD emission is observed. This effect is explained in terms of the enhancement of two-photon absorption in QDs due to the full confinement of carriers. Furthermore, evidence of the presence of excited states is revealed from the two-photon photoluminescence excitation spectra presented in the study. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We present a study of the time-integrated and time-resolved photo luminescence properties of single-InGaN/GaN quantum dots (QDs) using two-photon spectroscopy. Two samples containing QDs produced by different growth techniques are examined. We find that two-photon excitation results in the suppression of the emission from the underlying quantum well to which the QDs are coupled and yet relatively strong QD emission is observed. This effect is explained in terms of the enhancement of two-photon absorption in QDs due to the full confinement of carriers. Furthermore, evidence of the presence of excited states is revealed from the two-photon photoluminescence excitation spectra presented in the study. (c) 2006 Elsevier B.V. All rights reserved.