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Title: Germanium-tin-silicon epitaxial structures grown on silicon by reduced pressure chemical vapour deposition
Author: Patchett, David
ISNI:       0000 0004 6423 0200
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2016
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Crystalline germanium-tin (GeSn) binary alloys have been subject to a significant research effort in recent years. This research effort is motivated by the myriad of potential applications that GeSn alloys offer. Crystalline epitaxial layers of GeSn and silicon-germanium-tin (SiGeSn) have been grown onto Si(001) substrates on a relaxed Ge buffer using reduced pressure CVD and commercially available precursors. X-ray diffraction, transmission electron microscopy, atomic force microscopy, secondary ion mass spectrometry and Raman spectroscopy were used to determine layer composition, layer thickness, crystallinity, degree of strain relaxation, surface features and roughness of the samples investigated in this work. The epilayers produced have been both fully strained to their growth platform and partially relaxed. The Sn fraction of the alloy layers varied from 1 to 12 at. % Sn. Using N2 as the carrier gas during growth is observed to inhibit Ge1-xSnx growth. Off-axis substrates are determined to hinder the production of crystalline layers of GeSn. In-situ material characterization of GeSn layers during thermal treatment has identified the existence of a critical temperature for higher Sn fraction layers, beyond which the material quality degrades rapidly. This critical temperature is dependent on the layer composition, layer thickness, layer strain state and annealing environment. Layers of germanium-tin-oxide are produced by thermal oxidation and shown to have similar oxide formation rates to pure Ge. The low thermal budget limit for the high Sn fraction alloys has driven research into forming Ohmic metal contacts on GeSn layers with processes limited to low temperatures. Gold is determined to be the optimum electrical contact material.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics