Examination of the Feasibility of Transferred Electron Devices for Optoelectronic Interaction: Theory and Experiment

Kilburn, Matthew (1994) Examination of the Feasibility of Transferred Electron Devices for Optoelectronic Interaction: Theory and Experiment. PhD thesis, University of Glasgow.

Abstract

The engineering feasibility of Transferred Electron Devices (TEDs), configured as modulators, was explored. Vertical and planar implementations of the same device were pursued concurrently. An existing "side-wall bonding pad" vertical device was replaced by a revised structure, incorporating dual anode contacts and dielectric isolation. Natural self-resonant frequency inhibition with device capacitance was assessed for both of these vertical devices. The reappraisal was shown to provide benefits of reduced capacitance, reduced current capacity and greater symmetry of the electric field distribution in the active region. Modelling of the optical confinement attributes of rib waveguides for device designs was performed using the FWAVE III and LWAVE application programs. Confinement afforded by the rib-substrate interface and 33% AlGaAs layers, in vertical and planar devices respectively, was determined for multi-moded propagation. Efficiently confmed propagation at infrared wavelengths was observed. Theoretical predictions for modulation depths were calculated for rib waveguide devices. The modulation potential of mechanisms such as Pockels effect, Franz-Keldysh electro-absorption and free carrier influences were analysed. These evaluations were made employing very idealised conditions, leading to consistent over-estimates of modulation indices. The requirements for deep modulation were identified in the context of the engineering designs of real devices. The prospect for voltage-controlled frequency modulation in planar devices, required the development of analytical theory for tapered (graded area) devices. The functional variation of the pre threshold electric field distribution was obtained. This permitted the derivation of a predictive current-voltage function for a general transferred electron device with defined semiconductor and physical parameters. The time constant governing growth / decay of nucleated disturbances in tapered devices was sought, verifying the possibility of transit mode operation, A fully calculable function, encapsulating the influences of inter-valley transfer and dipole formation, was developed and quoted. Both vertical and planar devices were fabricated and assessed experimentally. The theoretical current voltage function was used as a fulcrum for the analysis of the influence of the cathode boundary conditions in planar devices. The behaviour of graded and non-graded elements was modified by varying the annealing conditions in a standard contact metal recipe. A mechanism was conjectured to explain these variations in the context of the Kroemer hypothesis. The resulting empirical functions were used to assess the inhibition of injected electrons at the cathode. Endfire analysis was performed on waveguide devices, with electrical biassing applied in-situ. In response to theoretical thermal modelling, in conjunction with practical observations of real devices, a circular mesa form of waveguide device was proposed and fabricated. Estimates of maximum permissible pulse width were made, assisted by Laplace transform analysis of a thermal - electrical analogue circuit. A simple formula for rib-substrate thermal resistance was derived for this analysis. Permissible pulse widths were demonstrated to be incompatible with the notion of a viable modulator operating near to CW.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Peter Leybourn
• Keywords: Electrical engineering
• Date of Award: 1994
• Depositing User: Enlighten Team
• Unique ID: glathesis:1994-75284
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 21:20
• Last Modified: 19 Nov 2019 21:20
• URI: https://theses.gla.ac.uk/id/eprint/75284