Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638344
Title: An investigation of Delta-doped field effect transistors
Author: Nutt, H. C.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1991
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Abstract:
In this work two novel gallium arsenide field effect transistor (FET) structures have been investigated. Both single and double plane delta-doped device layers were grown by molecular beam epitaxy, processed into devices and then D.C. characterized. The simplified analytical D.C. device theory of the single delta-doped device was utilised to explain the experimental device performance. These devices gave high currents and good pinch-off. The single delta-doped device had a constant transconductance over a wide range of gate biases, the value of which was approximately inversely proportional to the gate-plane separation. The double plane devices, on the other hand, had two regions of constant transconductance. Delta-doped samples, similar in design to the device wafers, were grown and then assessed using secondary ion mass spectrometry (S.I.M.S.), room temperature and variable temperature Hall measurements and electrochemical carrier profiling. The mobility enhancement as a function of delta-doping density, carrier concentration saturation and the diffusion of silicon away from the plane within this material were investigated. A two-step diffusion model was developed to model the diffusion of the silicon away from the plane that occurs during the deposition and overgrowth in the case of low doped delta-layers. All the silicon in these low-doped layers was found to be electrically active. It is proposed that silicon diffuses substitutionally on the gallium sublattice. The higher-doped delta-layers were analysed using a graphical technique, as the SIMS profiles could not be approximated by the two-step diffusion model. This revealed an additional faster diffusion mechanism. It was found that a high proportion of the silicon was electrically inactive. It is suggested that in addition to single silicon atoms diffusing on both gallium and arsenic sublattices, a faster pair diffusion mechanism was operating.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.638344  DOI: Not available
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