EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF QUANTUM TRANSPORT IN SHALLOW AND DEEP DONOR BASED SINGLE ELECTRON TRANSISTORS

Abstract

Technological growth has developed at an exceptional rate during the last few decades. Moore's law has reached its physical limit, but the reduced feature size of devices has enabled us to exploit the atomic scale properties. The new-age devices explore more fundamental roles of individual atoms. From the perspective of physics, quantum devices take advantage of quantum mechanical rules and devices are engineered with more atomic precision and offer various potential applications. Prof. Bruce Kane presented a solid-state quantum computer architecture using phosphorus donors in silicon. After this scheme, the donor deployed devices have grown phenomenally and their developments in various applications are proposed. Studying the transport behavior of such nanoscale devices is an interesting scientific problem. In the thesis, we focused on such dopant atom based single electron transistors (SETs). SET is studied as an essential and functional component in various quantum devices and has tremendous implications. To this date, SETs in the donor atom-based silicon and other systems are theoretically realized and experimentally demonstrated in vast. In the present work, we studied dopant atom-based silicon transistors and their related phenomena. The main objective of this work is to investigate the shallow dopant-based SET and to overcome their low temperature operation by the alternative deep dopant system. We addressed the problem of low barrier height due to the shallow nature of donor i.e., phosphorus. Using the rate equation approach, we numerically simulated the ideal (infinite barrier) system. We constructed a variable barrier dependent tunnel rate and used it in the rate equation to depict the practical device results with some examples. We also studied a phosphorus-doped single electron tunneling device and observed the inelastic cotunneling phenomena occurring in this device. The detailed investigation led to inelastic cotunneling phenomena giving a resonance like leakage current. We constructed an exact model to explain the physics behind this result. Conventional silicon impurities-based SETs (like phosphorus, boron, and arsenic) suffer from low binding and charging energies. The room temperature thermal energy hinders the applications of such shallow donor-based devices. However, the confinements (quantum and dielectric) are adopted to make devices work at room temperature, but we focused on alternative deep donor in silicon where the charging and binding energies are naturally manifold. We proposed and studied nitrogen as a deep donor in silicon for such devices. We theoretically investigated the transport characteristics of such nitrogen doped silicon device and obtained the adequate transport behavior at room temperature. For the experimental demonstration of nitrogen donors in silicon, we deposited the nitrogen-containing species on silicon and, after annealing, confirmed the nanoscale doping in silicon by various techniques. After successfully implementing nitrogen doping in silicon, we plan to fabricate a nitrogen based single electron tunneling device.