91̽»¨

Abstract:

Most experts agree that it is too early to say how quantum computers will eventually be built, and several nanoscale solid-state schemes are being implemented in a range of materials. Nanofabricated quantum dots can be made in designer configurations, with established technology for controlling interactions and for reading out results. Epitaxial quantum dots can be grown in vertical arrays in semiconductors, and ultrafast optical techniques are available for controlling and measuring their excitations. Single-walled carbon nanotubes can be used for molecular self-assembly of endohedral fullerenes, which can embody quantum information in the electron spin. The challenges of individual addressing in such tiny structures could rapidly become intractable with increasing numbers of qubits, but these schemes are amenable to global addressing methods for computation.

Abstract:

The Kerr gate technique is used to time-resolve the gain in an In0.02Ga0.98N/In0.16Ga0.84N multiple quantum well sample. A new way of analyzing the data in such a variable stripe length method gain experiment is used to analyze the time-resolved spectra. The dynamics of the emission and gain are discussed. These measurements suggest that the photoexcited carriers must localize (possibly at indium-rich sites) before strong stimulated emission is seen. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

The Kerr gate technique is used to time-resolve the gain in an In0.02Ga0.98N/In0.16Ga0.84N multiple quantum well sample. A new way of analyzing the data in such a variable stripe length method gain experiment is used to analyze the time-resolved spectra. The dynamics of the emission and gain are discussed. These measurements suggest that the photoexcited carriers must localize (possibly at indium-rich sites) before strong stimulated emission is seen. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We have studied the growth of InGaN epitaxial layers on GaN by MOVPE (metal-organic vapour phase epitaxy), and have discovered that nanostructures may be formed if a flat epilayer is annealed in molecular nitrogen immediately after growth. The size and density of the nanostructures are shown to be dependent on the growth/anneal temperature. We demonstrated the quantum dot nature of our nanostructures by performing spatially resolved photoluminescence on samples that had been capped with a layer of GaN, grown at the same temperature as the InGaN epilayer. This revealed narrow, delta-function-like lines in the luminescence spectrum with full width at half maximum (FWHM) limited by the resolution of the spectrometer at 4.2 K. Measurement of the FWHM as a function of temperature revealed significant broadening above 20 K. (C) 2003 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim