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Title: Characterisation and advanced applications of the steam oxidation of AlGaAs
Author: Michell, Gareth J.
ISNI:       0000 0004 2750 548X
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2010
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The high temperature, wet oxidation of buried, high aluminium content AlGaAs layers has seen a lot of attention in recent years thanks to its ability to form good quality, deep and uniform oxide layers a unique attribute among the III-V materials. It is the unusual combination of relatively high density and good porosity of the oxide material, that allows the oxidation to reach much greater depths than that of other materials, and this is what makes the process so widely employable and versatile. This project is based on two systems of oxidisable layers, incorporated into two wafers, both of which were designed as part of the work. One wafer, referred to as Wafer A, contains 30nm 98% aluminium layers in both of the cladding regions, and the second, Wafer B, has spaced stacks of 1nm 95% aluminium layers placed directly into the active region. The oxidation depths of both wafers are mapped over a range of temperatures and times, and maximum measured rates of 2um/min and 1um/min are reported for Wafers A and B respectively. Further to this, a non-trivial dependence of the oxidation rate on dopant species is reported. It is found that although p-type material initially achieves greater oxidation rates, after a depth of approximately 8pm has been reached, the n-type material over takes. This result is contrary to the popular belief that p-type material oxidises faster, regardless of depth. The two wafers are then made into working devices. In the case of Wafer A, longitudinal oxidation of broad-area devices are used to create unpumped saturable absorber sections. These sections are responsible for various effects including the lowering of laser threshold currents by up to 30%, the narrowing of laser near-fields by up to 50%, and the production of repetitive wavelength shifting behaviour, which is investigated in great detail. Wafer B is oxidised laterally to produce current confinement directly in the active region. Threshold current reductions of around 20% are recorded. Lastly, cross-sectional electron microscope images reveal a simple and versatile method of fabricating buried microlenses from the structure of Wafer B.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available