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Title: Silicon heterostructure intersubband emitters
Author: Bates, R.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2003
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It is believed that the Silicon Germanium (SiGe) materials system offers numerous benefits over GaAs/AlGaAs for operation within the THz gap - absorption coefficients are lower due to the non-polar nature of the SiGe lattice and the potential for integration with Si chips exists. Furthermore, operating within the valence band allows surface normal emission to be observed and vertical cavity surface emitting lasers to be fabricated using transitions between light (LH) and heavy (HH) hole subbands and poly-Si/silicon dioxide Bragg reflectors. This dissertation reports upon recent advances made in FIR Quantum Cascade Emitters (QCEs) based within the SiGe materials system. Initial measurements were designed purely to demonstrate the ability of the vertical intersubband transition to absorb radiation. Such structures were also observed to emit and spectroscopy was performed allowing the origin of such emission to be verified as being due to intersubband transitions. QCEs were then designed and processed, allowing the observation of the first surface-normal emission from a QCE in the absence of a grating to be observed. Further designs demonstrated the primary dependence upon the strain within the quantum wells of the energy of the LH1-HH1 transition. The scalability of the active regions has also been demonstrated - the strain symmeterised growth allowing hundreds of layers to be grown at a uniformly high standard. A shift from vertical (intrawell) to diagonal (interwell) transitions using photon assisted tunnelling lead to the theoretical observation of population inversion within the system. One of the key requirements for lasing, the existence of population inversion demonstrates both the potential and feasibility for a QCL to be fabricated in SiGe.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available