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Gallium nitride processing for high power microwave devices

Farrant, Luke. 2005. Gallium nitride processing for high power microwave devices. PhD Thesis, Cardiff University.

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Abstract

This thesis contains literature reviews relating to inductively coupled plasmas and their use in etching gallium nitride with chlorine based plasmas. The properties of gallium nitride, how these properties make gallium nitride a suitable material for high power microwave transistors and how such transistors will help improve the systems in which they might be used are also reviewed. In this thesis, a novel, non-destructive method of measurement of the conductivity of a semiconductor through measurement of the increase in the bandwidth of the resonant peak of a microwave dielectric resonator when it is brought near a semiconductor wafer is presented. Using this method the conductivity of a thin gallium nitride film is obtained and found to be within the expected range it was found to be very difficult to measure the conductivity of this gallium nitride wafer using a four-point probe, as the film was too thin. Also presented in this thesis are studies of the etch characteristics of gallium nitride and photoresist in mixed boron trichloride and chlorine plasmas generated in two Oxford Instruments inductively coupled plasma etchers (ICP 180 and 380). The ICP 380 was used to etch the mesa isolation of gallium nitride based heteroj unction field effect transistors that were fabricated at Cardiff University. A method of making the angle of the mesa sidewall acute by melting of the photoresist is presented. An acute mesa-sidewall angle facilitated the easy traverse of the mesa edge by the gate metal. Characterisations of ohmic and Schottky contacts that were fabricated as part of the effort to produce a working gallium nitride based heteroj unction field effect transistor are presented and reasons given for the failure of some of the ohmic contacts. The dc characteristics of the best transistor fabricated during the project are presented.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
ISBN: 9781303207044
Funders: Cardiff University School of Engineering, Oxford Instruments Plasma Technology
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:15
URI: http://orca.cardiff.ac.uk/id/eprint/56118

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