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Excited State Spectroscopy and Optical Bleaching in c-axis divacancies in Silicon Carbide

Adema, J.A.H. (2016) Excited State Spectroscopy and Optical Bleaching in c-axis divacancies in Silicon Carbide. Bachelor's Thesis, Applied Physics.

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C-axis divacancy bound electron spins in Silicon Carbide (SiC) have interesting properties for quantum information applications. SiC is a material well known to large scale industrial processing and spin states in the ground state of the divacancy show coherence times (T2 ∗) up to the millisecond scale. This thesis addresses two main issues regarding optical manipulation ensembles of c-axis divacancies in SiC: the process of charge state switching (optical bleaching and repumping) and the yet unknown excited state structure of c-axis divacancies. Using several rates of illumination, optical bleaching processes were analyzed by fitting bleaching traces to an exponential decay, with a decay constant depending on transition linewidth, laser field spatial distribution and the power of laser intensity. The model along which the bleaching process was fitted was not able to make a perfect fit attributed to other absorption processes, especially not for higher laser intensities. By considering the best fit of the model to the bleaching traces and the shape of the bleaching curves for different powers of the intensity, it was found that a single photon process is probably underlying the bleaching process. Possible excitations that could cause bleaching effect have been proposed and suggestions for improvement of the method to investigate which processes cause both charge state switching effects have been posed. The repump process was not considered thoroughly due to absence of a continuous wave laser in the range of optical wavelengths able to restore the divacancies in the resonant charge state. Magneto-spectroscopy was performed to evaluate the excited state structure by considering electronic levels and transitions and their respective spin pumping features. Using a lock-in technique in transmission, the persistent absorption by electrons which underlied spin pump features was probed by magneto-spectroscopy. These features did not correspond to features expected as the result of a triplet-triplet electronic structure, but belonged to two different sets of carrier frequencies. To explain this behavior, three possible hypotheses are posed: a manifold excited state with differing transition strengths and Inter System Crossing (ISC) strengths, two different physical defects with both a triplet excited state with differing transition and ISC strengths and a single defect where local strain discontinuously alters the transition and ISC strengths and electronic structure. Moreover, several suggestions for testing these hypotheses are given.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Applied Physics
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 08:30
Last Modified: 15 Feb 2018 08:30

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