Nanoscale optical devices based on phase coherent electron transport
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Alam, Mahbub
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Abstract
The optical interaction of phase coherent electron in an open system has been investigated. It has been found that after optical excitation electron wavefunction evolves in a coherent manner in excited state and quantum interference of phase coherent electrons after optical excitation gives rise to periodic oscillation in photocurrent as a function of illumination length. This periodic oscillation results in illumination length dependent optical absorption for a material at illumination length around the Bloch wavelength of participating electrons. Under sub Bloch wavelength illumination, which has been investigated to be experimentally achievable with nanoplasmonic focusing, of a particular structure, where a gate potential has been applied in half of the device, the quantum interference of electrons can be utilized to manufacture new kinds of photodetectors where current in the external circuit changes direction with change in wavelength of light. This is a completely new phenomenon and only achievable with coherent wave-nature of electron and sub Bloch wavelength illumination. Momentum conserved transition has not been found as a necessary requirement for optical transition for Bloch scale illumination as momentum of the electron is not defined for ultra-small scale illumination. From the uncertainty of position and momentum of electron in the illumination area, a way of verifying Heisenberg uncertainty principle via optical absorption has been suggested under ultra-small scale illumination. Also, the coupling of longitudinal resonant modes, which arises from phase coherent electron transport in a Mach Zehnder interferometer structure, has been investigated for manufacturing a p-n junctionless, high quantum efficiency photodetector. A new spectrometer device under coherent electron transport regime which can detect and distinguish light of different frequencies has also been discussed. A new study field called opto coherent electronics has been proposed.
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Date
2016-08-25
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Dissertation