This thesis reports the development of two rapid thermal annealing systems, one based on resistive heating of graphite strips, the second on heating from incoherent lamp radiation. Electrical activation studies of silicon implanted gallium arsenide has been used to compare the systems with those available commercially. It has been shown that commercial systems can yield temperature measurement errors in excess of 50° C. Furthermore, the systems have been used to investigate the electrical activation of silicon implants co-implanted with other ions into gallium arsenide, with a view to either, improving the activation of the silicon for high doses, or modifying the carrier profile shape for low doses. A factor of two improvement in the electrical activation of high dose silicon implants has been achieved by the co-implantation of phosphorus, with a reduction in the annealing temperature required to achieve a given activity also being observed. An alternative processing methodology is also proposed for through- nitride implantation. Phosphorus implants have also been used to "pre-amorphise" substrates to prevent ion channelling. Providing the damage is maintained below a certain level, improvements in profile shape can be obtained. Other compensation techniques using boron and carbon implants have also been investigated. Boron has been demonstrated to provide improved carrier activation for low implant doses, with thermally stable profile modification capability as the dose is increased. The electrical activation of single carbon implants (40% maximum) is below the level of compensation of silicon implants (approximately 90%) co-implanted with carbon. This in turn means carbon is excellent for profile modification as no p-type layer is created beyond the donor implant.

The incorporation of Si1-xGex alloy heterostructures into conventional Si processes has been proposed as a means of improving the operating frequency and overall performance of Si field effect transistors. One parameter expected to benefit from this approach is the hole mobility, which would have important implications for high speed CMOS applications. Measured values of the hole mobility, however, have failed to live up to early expectations, and much ongoing research is directed at understanding whether this is an intrinsic limitation (e.g. due to alloy disorder scattering), or due to imperfections arising in the growth and fabrication process. In this thesis, a detailed theoretical study is presented of the hole mobility in single sub-band Si1-xGex heterostructures.

The increasing demand for high performance as well as low standby power devices has been the main reason for the aggressive scaling of conventional CMOS transistors. Current devices are at the 32nm technology node. However, due to physical limitations as well as increase in short-channel effects, leakage, power dissipation, this scaling trend cannot continue and will eventually hit a barrier. In order to overcome this, alternate device topologies have to be considered altogether. Extensive research on ultra thin body double gate FETs and gate all around nanowire FETs has shown a lot of promise. Under strong inversion, these devices have demonstrated increased performance over their bulk counterparts. This is mainly attributed to full carrier inversion in the body. However, these devices are still limited by lithographic and processing challenges making them unsuitable for commercial production. This thesis explores a unique device structure called the CFET (Cylindrical Field Effect Transistors) which also like the above, relies on complete inversion of carriers in the body/bulk. Using dual gates; an outer and an inner gate, full-volume inversion is possible with benefits such as enhanced drive currents, high Ion/Ioff ratios and reduced short channel effects.

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

As electronics reach nanometer size scales, new avenues of integrating biology and electronics become available. For example, nanoscale field-effect transistors have been integrated with single neurons to detect neural activity. Researchers have also used nanoscale materials to build electronic ears and noses. Another exciting development is the use of nanoscale biosensors for the point-of-care detection of disease biomarkers. This thesis addresses many issues that are relevant for electrical sensing applications in biological environments. As an experimental platform we have used carbon nanotube field-effect transistors for the detection of biological proteins. Using this experimental platform we have probed many of properties that control sensor function, such as surface potentials, the response of field effect transistors to absorbed material, and the mass transport of proteins. Field effect transistor biosensors are a topic of active research, and were first demonstrated in 1962. Despite decades of research, the mass transport of proteins onto a sensor surface has not been quantified experimentally, and theoretical modeling has not been reconciled with some notable experiments. Protein transport is an important issue because signals from low analyte concentrations can take hours to develop. Guided by mass transport modeling we modified our sensors to demonstrate a 2.5 fold improvement in sensor response time. It is easy to imagine a 25 fold improvement in sensor response time using more advanced existing fabrication techniques. This improvement would allow for the detection of low concentrations of analyte on the order of minutes instead of hours, and will open the door point-of-care biosensors. / Graduation date: 2011

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