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Title: Electrical transport properties of two-dimensional hole gases in the Si/Si₁₋ₓGeₓ system
Author: Emeleus, Charles John
ISNI:       0000 0001 3447 3744
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1993
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This thesis is a report of experimental investigations of hole transport properties in quantum wells formed in Si/SiGe heterostructures grown by Molecular Beam Epitaxy. Initial work was concerned with elucidating the dominant hole scattering mechanisms, the aim being to relate this to the growth conditions and consequently produce enhanced mobility material for further study. Accordingly, low temperature resistance and Hall measurements (down to 4 K) were undertaken, in order to minimise the effect of phonon scattering. The first samples exhibited strongly localised hole states at liquid helium temperatures, but subsequently, the introduction of growth interrupts as well as the use of higher growth temperatures was shown to give rise to conduction by extended states, with a maximum 5 K mobility of nearly 4000 cm2V',s1. Interface impurities at the Si/SiGe heterojunction with a density of 2xl0n cm-2 are shown to be responsible for the typical carrier mobility of 2000 cm:V-'s'1 obtained in structures grown at 550 °C, and using a model developed by the author this density is found to be consistent with the dependence of experimental data on structural and doping parameters. Magnetotransport measurements carried out in fields up to 12 T in strength and at temperatures down to 0.3 K yielded the first observation of weak localisation and carrier-carrier interaction phenomena in this materials system. It is possible to confirm that strain lifts the light hole and heavy hole band degeneracy associated with unstrained Si. In addition, a temperature dependence of the Boltzmann conductivity is observed and attributed to the variation of screening efficiency with thermal disorder. Deviations from the expected InT dependence of the Hall coefficient in the presence of enhanced interaction phenomena might be understood in terms of a recent theory for the weak localisation correction to the Hall conductivity near the metal-insulator transition.
Supervisor: Not available Sponsor: Science and Engineering Research Council ; British Telecom
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics