Jeffrey Frederick Gold
University of Cambridge
Microelectronics Research Centre
Cambridge CB3 0HE
The following manuscript was submitted as part of the MPhil program in Microelectronic Engineering and Semiconductor Physics at the Microelectronics Research Centre (MRC) of the Cavendish Laboratory at the University of Cambridge. The manuscript is a literature survey undertaken by the author as part of the MESP program during Lent term 1997 and is the basis of a talk of the same
title given at the MRC on January 20, 1997.