Electronic transport properties of graphene-based heterostructures
[Thesis]. Manchester, UK: The University of Manchester; 2013.
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Heterostructures fabricated from atomically thin crystalline layers are new materials which offer exciting possibilities for next-generation electronic and optoelectronic sensors and devices. The idea of heterostructures is not new and traditional semiconductor heterostructures have already played an important technological role in many modern electronic components. It is possible to fabricate new and exciting structures by stacking single atomic layers of different materials into heterostructures. This technology can be used to create materials and devices with a wide variety of properties. The stacking order, thickness, doping and crystal orientation play the major roles in determining the characteristics of these new materials. The experimental work for this thesis involves the electrical characterisation of several different heterostructures.i Investigation of boron nitride as an atomically thin tunnel barrier, including its homogeneity across micron sized areas. The area normalised conductance was found to depend on boron nitride thickness, changing by 1.5 decades per layer.ii Graphene-based tunnelling transistors which exhibit current modulation by external gate voltage. With boron nitride as the tunnel barrier an on-off ratio of up to 40 was acheived.iii Resonant tunnelling devices which show negative differential conductivity in their current-voltage characteristics.iv Photodetection and solar cell devices using semiconducting tungsten disulfide. The maximum external quantum efficiency observed was 0.1 A/W which was approximately constant across the visible spectrum. The enormous array of possibilities made available by this technology means that there is huge scope for further investigation with more exploratory research to make proof-of-principle functional devices for application in technology.