Growth of terrace graded virtual substrates, pioneered by Capewell (2002), has been conducted utilising solid-source molecular beam epitaxy (SS-MBE) to produce structures of higher germanium composition (up to pure germanium) and greater thickness (up to 20 μm) than previously investigated. Terrace grading offers a number of advantages over more conventional grading techniques which include the reduction of surface threading dislocation density, reduction of surface roughness and the possibility of the complete elimination of threading dislocation pile-up. The closely spaced pile-up of threading dislocations is believed to have a significant impact on the electrical properties of processed devices, and its elimination is a key goal in this work.\ud \ud Numerous terrace graded virtual substrate compositions have been grown and characterised during the course of this work and, where appropriate, comparison made with more conventional structures. The complete elimination of threading dislocation pile-up has been demonstrated at compositions of 30% and 40%, with a reduced threading dislocation density in comparison to equivalent liner graded structures. A major reduction in threading dislocation density has been accomplished though post growth ex-situ annealing at 900°c for an extend period of time, though the exact mechanism remains uncertain. The possible role of surface precipitates enabling reduction of dislocation pile-up and/or density is considered along with the effects of unwanted particulate contamination during growth
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