Applications modelling of advanced multilayer semiconductor structures - The bulk unipolar devices

Abstract

The research described in this thesis addresses "hot" electron diodes, otherwise known as Bulk Unipolar Diodes (BUD's), which require the formation of narrow, highly doped layers in a semiconductor with abrupt transitions from one doping level to another. A review of the properties of this family of devices is undertaken and since a BUD is formed by a narrow plane of ionised impurities within a semiconductor, analysis show that it is possible to control the in-built barrier electrostatically via a gate located in the vicinity of the barrier region (p-plane region). A study of the role of injected minority carriers has been applied in two areas, deployed in the two-state switch and the photodetector applications.
An investigation of the switching characteristics of the Bulk Unipolar Switch (BUS) and various device design parameters using an empirical formula, is presented for Computer-Aided-Design (CAD). The model has been shown to simulate all the critical points on the I/V characteristic and the reconstruction is in good agreement with published results.
The p-plane BUD structure is analysed in detail and the results from numerical methods are given for the device by modifying various design parameters. Objective assessment has lead to the development of a novel p-plane photodetector where the internal gain is due to optical modulation of the potential barrier inside the bulk material via the diffusion and thermionic emission theories for the first time. Qualitative analysis of how optically generated holes in the vicinity of the p t-plane have the effect of lowering the height of the potential barrier, are presented. Results from analysis show the
dependence of the high gain on the modulation of the barrier.