Optical and magnetic resonance studies of point defects in CVD diamond

• Main Author: D'Haenens-Johansson, Ulrika F. S
• Format: Dissertation
• Language: English
• Published: University of Warwick 2011
• Subjects: QC Physics

This thesis reports research conducted on point defects in single crystal diamond utilising the complementary techniques of electron paramagnetic resonance (EPR), optical absorption and photoluminescence (PL) spectroscopy. Intentional silicon-doping of chemical vapour deposition (CVD) diamond allowed the production of samples grown on differently oriented substrates and containing distinct silicon isotopic abundances. The EPR spectrum of the neutral charge state of the silicon split-vacancy centre in diamond, (Si-V)0, has been characterised in the literature. Evidence for the assignment of the 1.31 eV zero phonon line (ZPL) seen in absorption and PL to the 3A2g -> 3A1u transition arising at (Si-V)0 is presented. Reversible charge transfer between the negatively charged centre, (Si-V)− (ZPL at 1.68 eV), and (Si-V)0 enabled the determination of calibration factors relating defect concentrations to their respective ZPL intensities. Preferential alignment of trigonal centres, such as (Si-V), in CVD material grown on {110}-substrates has been observed. The formation of (Si-V) centres during CVD synthesis and via irradiation and annealing of silicon-doped diamond was studied. Variable temperature EPR spectroscopy under illumination was used to investigate the optical spin polarisation (SP) of the (Si-V)0 3A2g ground state. Two different mechanisms for the SP are considered; selective intersystem crossing of (Si-V)0, and photoionisation of (Si-V)−. The properties of (Si-V)0 are compared to those of the extensively studied negatively charged nitrogen vacancy centre, (N-V)−. The effective spin-lattice relaxation and spin polarisation rates for both centres during continuous illumination are explored using pulsed EPR methods. A new defect, labelledWAR3, with spin S = 1 2 was observed in silicon-doped diamond and characterised using multifrequency EPR. Analysis of the data revealed that WAR3 is the neutral charge state of a silicon divacancy complex decorated by a hydrogen atom, (Si-V2:H)0. The experimentally derived 29Si and 1H hyperfine parameters are in good agreement with the values calculated using the spindensity- functional technique, confirming this model and ruling out a non-planar structure.