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Terahertz radiation has many uses in a broad range of fields including medicine and healthcare security, earth science, production monitoring and astronomy. The use of terahertz in many of these applications has been precluded by the lack of an inexpensive source that can operate without cryogenic cooling. If a Si-based terahertz quantum cascade laser could be developed, it is a likely candidate to fill this role. It is possible that the largest challenge facing the development of a Si-based quantum cascade laser is that of the demand requiring epitaxial growth. The main achievement of this study is the growth of challenging n-type Ge/Si1-xGex superlattice structures which are intended for terahertz emission. Comprehensive materials characterisation is presented for the structures. The final structures have been sent to collaborators for further characterisation and to be processed into devices. The results of which will be used to optimise future growth of Si-based QCL structures. The effects of the low temperature used in the growth of the QCL structures on the critical thickness is investigated and Si0.4Ge0.6/Si layers grown far beyond the critical thickness predicted by theory are presented. These layers have applications in electronic devices such as field effect transistors (FETs). The fabrication and characterisation of flat, single crystal Ge membranes is presented. The strain, membrane thickness, crystalline tilt and crystalline quality are determined by micro-diffraction, performed on the membranes at Beamline B16 at the Diamond Light Source. These membranes are shown to be of high crystal quality which gives them many applications, including as a possible platform for Si-based quantum cascade laser structures. |
