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Title: Novel grading of silicon germanium for high quality virtual substrates
Author: Capewell, Adam Daniel
ISNI:       0000 0001 3519 3197
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2002
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The growth of SiGe virtual substrates, by solid-source molecular beam epitaxy (SS-MBE), using a new germanium grading technique has been studied. It is proposed that the grading of germanium using a series of linearly graded/uniform layers (terrace grading) prevents the dislocation pile-ups, associated with strain relief, from penetrating the entire epilayer. Since the dislocation pile-ups cause threading dislocations to become trapped and increase the roughness of the surface, the control of these pile-ups reduces both the threading dislocation density and the RMS surface roughness. Si0.50Ge0.50 virtual substrates of 2 µm thickness using the terrace grading technique have been studied and compared to conventional linear graded and step graded virtual substrates of the same thickness. Substantial reductions in both the RMS roughness and threading dislocation densities are found in the terrace graded structure, compared with the conventional techniques. Electrical properties have been measured in layers grown on virtual substrates using the terrace grading and show promisingly high hole mobilities. The mechanism by which the terrace graded virtual substrates relax has been examined in order to optimise the growth conditions. It is found that the lowest layers of the virtual substrates do not relax until sufficient strain energy is accumulated by the growth of the following layers, leading to dislocation pile-ups that extend through several layers. The use of in-situ anneals has been shown to greatly improve the relaxation of the lower layers, with a corresponding decrease in the size of the pile-ups, and consequently lower threading dislocation densities have been found.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics