Electron spin coherence in bulk silicon and silicon heterostructures

Multiple proposals in quantum information science use electron spin qubits in silicon, because of the long relaxation (T1) and coherence (T2) times expected. However, this expectation is based on measurements of isolated, tightly bound spins in bulk silicon, whereas spins in realistic architectures will be in a noisier environment, for example in a loosely bound quantum dot or exchange coupled to neighbors, which may shorten the times. This thesis contributes to the field by describing pulsed electron spin resonance (ESR) measurements of the T1 and T 2 of two spin species which are affected by these environmental noise sources.;The first measurement was performed on electrons in the channel of a Metal-Oxide-Silicon (MOS) transistor. A new ESR signal was seen, arising from mobile two-dimensional electrons at the Si/SiO2 interface. By choosing appropriate conditions, the electrons could also be confined by the interface disorder into natural quantum dots, with similar ESR signatures. T1 and T2 for mobile electrons and natural dots were measured at temperatures down to 350 mK. The dots show a T1 of 0:8 ms at 350mK that is four orders of magnitude longer than mobile electrons; a promising result for proposals that use quantum dots in silicon. However, the longest T2 for natural dots is 30 mus, significantly shorter than T1. The reason for this short T2 remains to be identified.;The second measurement was performed on electrons bound to exchange coupled phosphorus dimers in bulk isotopically enriched 28Si. The narrow linewidth in 28Si improved the ESR resolution, allowing us to measure a hitherto unseen fine structure to the dimer ESR line. This new structure is explained to arise from weak second order effects in the dimer spin Hamiltonian, combined with the broad range of exchange couplings among dimers present in the sample. Next, pulsed ESR was performed on the dimers to measure T1 and T2 in the presence of exchange coupling. The times are identical to those for isolated phosphorus donors, indicating that within the limits of our experiment, exchange coupling does not reduce spin coherence.