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Magneto-spectroscopy of strain-induced quantum wires and dots.

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Call No.	QC176.8.Q35 G46 1996
Author	Gfroerer, Timothy Hurley.
Title	Magneto-spectroscopy of strain-induced quantum wires and dots.
Date	1996
Abstract	Magneto-spectroscopy is used to characterize the confinement properties of strain-induced quantum wires and dots. The wires and dots are low energy regions in an ordinary GaAs/AlGaAs quantum well that are formed when microscopic compressively-strained structures (""stressors"") on the surface of the semiconductor relax. The magnetic field gives rise to additional terms in the Hamiltonian of the system which compete with the strain confinement and the Coulomb interaction between electrons and holes. For the excited states in the wires and dots, the field dependence is primarily determined by the interplay between the strain and magnetic confinement. At high fields, Landau quantization dominates and individual states are well resolved in the photoluminescence spectrum. When tungsten is used as the stressor material, slow relaxation of excited states is observed in the strain-induced quantum dots. I estimate that the energy loss rate in the tungsten dots is at least two orders smaller than that of the host quantum well. The reduced cooling is attributed to the discrete density of states in the quantum dot, together with the fact that the confined excitons are spatially too large to couple to phonons with the intersubband energy. When the average carrier density corresponds to several electron-hole pairs per dot, carrier-carrier interactions accelerate the relaxation process. The field dependence of the ground state exciton, i.e. the diamagnetic shift, is used to measure the lateral size of these states. When the magnetic field is small, it can be treated as a perturbation on the Coulomb binding. In this case, the diamagnetic shift of a hydrogen-like exciton is proportional to the average value of the distance between the electron and hole squared. Many of the strain-induced structures studied here, particularly the tungsten dots, exhibit smaller diamagnetic shifts than their host quantum wells. This phenomenon suggest that excitons in these structures are smaller and more tightly bound."
Description	viii, 143 leaves : ill. 28 cm
Format	application/pdf
Advisor	Sturge, Michael D.
Subject	Quantum wells. Semiconductors. Spectrum analysis.
College	Dartmouth College -- Department of Physics and Astronomy.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.1398

Title	Page 1
Full Text	MAGNETO-SPECTROSCOPY OF STRAIN-INDUCED QUANTUM WIRES AND DOTS A Thesis submitted to the Faculty in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physics and Astronomy by Timothy Hurley Gfroerer DARTMOUTH COLLEGE Hanover, New Hampshire February 2, 1996

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