This dissertation is concerned with the fabrication and physics of Molecular Beam Epitaxy (MBE) regrown semiconductor devices. I use the term regrown to refer to a structure which has been fabricated by MBE growth over a surface which has been <I>ex-situ </I>patterned. The structures presented in this dissertation can be subdivided into two broad categories: the narrow facet channels and the patterned back-gates. The narrow facet channels form part of a new class of devices, where the amphoteric nature of silicon dopant in the AlGaAs lattice is used to create lateral confinement. Growth of a GaAs A1GaAs heterostructure over a (311)<I>A</I> substrate, which is etched to expose a narrow (100) facet, results in the formation of a narrow two dimensional electron gas (2DEG) on the facet which is interspersed between two, two dimensional hole gases (2DHGs). The transport characteristics of the narrow 2DEG can be modulated by applying voltage to the adjacent hole gases, i.e. biasing either or both of the two dimensional p-n junctions formed between the 2DEG and 2DHGs. The actual width of the electron channel was found to be considerably smaller that the lithographic facet width. Theoretical modelling showed that this was a result of the fabrication and growth of the sample and not the electro-statics of the system. The inverse structure of a narrow 2DHG interspersed between two 2DHGs was also fabricated. The transport through the narrow 2DHG could be modulated in a similar manner. The patterned back-gated structures are the simplest illustration of the fabrication technique and are discussed first in the dissertation. The patterned back-gate is formed as islands of n<SUP>+</SUP> GaAs on an undoped GaAs substrate. Subsequently grown continuous layers are therefore guided in three dimensions over a wafer surface with regions of differing semiconductor compositions. This is a wafer scale fabrication technique, which completely dismisses the need for complicated lithography. The patterned back-gate was used to distinguish between the presence of an extended state formed between two 2DEGs and a second subband formed in one of the 2DEGs. The second subband was then used as a probe to characterise the regrowth interface. The series of back-gated long split gates showed quantisation plateaux illustrating the high quality of the samples fabricated using the regrowth technique.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598882 |
| Date | January 1997 |
| Creators | Evans, R. J. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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