Title Investigation of semiconductor nanostructures using terahertz and optical pulses /
Translation of Title Puslaidininkinių nanodarinių tyrimai terahercinės spinduliuotės ir optiniais impulsais.
Authors Žičkienė, Ieva
ISBN 9786090702772
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Pages 200
Keywords [eng] THz spectroscopy ; semiconductor nanowires ; LIPSS ; non-stoichiometric GaAs
Abstract [eng] The main purpose of the dissertation was to find out the cause of an enhancement of laser pulse induced THz pulse emission from nanostructured semiconductor surfaces. The studied nanostructures are divided into three groups: non-stoichiometric GaAs (NS GaAs); LIPSS on GaAs substrate (LIPSS - Laser Induced Periodic Surface Structures); perpendicular to the substrate surface InAs and InGaAs nanowires (NWs) and tilted GaAs NWs. During the preparation of dissertation the THz pulse emission from NS GaAs and LIPSS on GaAs was investigated for the first time. Also a modification of NS GaAs, which efficiently emits THz pulses even though the excitation beam falls perpendicular to the semiconductor surface, has been found. Moreover, a novel method to determine the orientation of a THz pulse emitting electric dipole in a respect to the substrate surface has been developed. It was found that the orientation of this dipole changes after the nanostructurization of semiconductor surface. It was concluded that more favourable dipole orientation is responsible for better THz emission from NS GaAs and LIPSS structures. Finally, it was found out that the entirety of laser-excited nanowires emit THz pulses as a thin layer with a particular refractive index n0. Since n0 is smaller than the refractive index of the substrate, the direction of THz generation becomes more favourable in respect to the THz emitting dipole axis which results in enhanced THz pulse emission.
Dissertation Institution Valstybinis mokslinių tyrimų institutas Fizinių ir technologijos mokslų centras.
Type Doctoral thesis
Language English
Publication date 2019