Year

1998

Degree Name

Doctor of Philosophy

Department

Department of Physics

Abstract

In this thesis, a new measurement technique is used to study the electronic properties of resonant tunneling heterostructures. The measurement technique incorporates an active operational amplifier circuit to simulate negative resistance and capacitance, and is used to probe regions of intrinsic bistability. Intrinsic bistability is observed in the experimental current-voltage characteristics of some resonant tunneling heterostructures when measured using conventional techniques.

The tunneling resonance characteristic of an asymmetric, double barrier resonant tunneling heterostructure which displays intrinsic bistability is shown to be smooth, continuous and multistable when measured using the new technique. It is the multistable region which is the main focus of this thesis. New features are measured within the multistable region, which remain inaccessible to conventional measurement techniques. The new features are shown to be associated with resonant tunneling via the excitation of a two dimensional plasmon in the central quantum well of the double barrier heterostructure. Such plasmon assisted tunneling is a previously unobserved tunneling mechanism in these heterostructures.

The first three chapters are concerned with the electronic properties of group III-V semiconductors, a brief background on resonant tunneling, and the experimental techniques employed in the studies. The fourth chapter discusses the details of the new measurement technique, the negative output resistance voltage supply and total circuit stability.

The final four chapters examine vertical transport, magnetotransport and optical properties of an asymmetric double barrier resonant tunneling heterostructure. Particular emphasis is placed on the bias direction which involves significant charge buildup in the central quantum well, and hence multistability, in the tunneling resonance. Significant minority carrier buildup under high excitation conditions is also discussed. Sample temperature variation, magnetic fields applied parallel and perpendicular to the layer plane, as well as photoluminescence spectroscopy are used in these studies.

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