Schottky enhanced photo-Dember terahertz emitters

Abstract

The unique properties of terahertz (THz) radiation make it useful for application in the field of imaging. The use of THz time-domain spectroscopy (THz-TDS) systems for the identification and characterisation of various materials is becoming more widespread, with this technology being applied in industry, security and scientific research. The common method for generating THz in commercial TDS systems is through the use of photoconductive antennas (PCA's). These are semiconductor-based devices capable of generating several W of power. PCA's require an external bias to generate a strong electric field across a small electrode gap. However, the high fields generated cause electromigration of the electrode metals and can result in damage to the antenna.

This thesis investigates the lateral photo-Dember (LPD) effect; a method of generating THz radiation from a semiconductor without the need for an applied electrical bias. The LPD effect relies on the difference in mobilities between electrons and holes to create opposing dipoles parallel to the semiconductor surface. The selective suppression of dipoles formed underneath a metal mask due to reflection then introduces the asymmetry required for observable THz radiation.

In this thesis the generation mechanism behind the LPD effect is investigated using 1D and 2D models, as well as the effect of the presence of a metal mask to suppress dipoles. The output from LPD emitters is enhanced through multiplexing and two different designs are investigated and fully characterised. The novel double-metal multiplexed emitters are then used to demonstrate THz beam shaping and focusing through control of the optical pump beam and a lensless THz-TDS system is proposed.

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Identifiers

ORCID for Paul C. Gow: orcid.org/0000-0002-3247-9082

ORCID for Vasileios Apostolopoulos: orcid.org/0000-0003-3733-2191

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