Multiple lateral photo-Dember terahertz emitters
Pulsed terahertz time-domain systems (THz-TDS) offer many applications for spectroscopy and imaging. Typically terahertz generation is achieved by using a photoconductive antenna to generate an electric field (of about 10 kV cm-1) across a semiconductor. By creating such an electric field electro-mi...
| Main Author: | |
|---|---|
| Other Authors: | |
| Published: |
University of Southampton
2016
|
| Subjects: | |
| Online Access: | https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682768 |
| Summary: | Pulsed terahertz time-domain systems (THz-TDS) offer many applications for spectroscopy and imaging. Typically terahertz generation is achieved by using a photoconductive antenna to generate an electric field (of about 10 kV cm-1) across a semiconductor. By creating such an electric field electro-migration occurs within the photoconductive antenna to eventually bridge the antenna electrodes. As a result photoconductive switches used for terahertz generation have a limited lifetime dependent on the voltage applied to them. This thesis investigates the lateral photo-Dember (LPD) effect as an alternative emitter that does not require an applied electric field. The photo-Dember effect relies on the difference in electron and hole mobility within semiconductors creating a current surge on photo-excitation. The lateral photo-Dember effect works by partially covering regions of the diffusion area to selectively suppresses the terahertz emission radiated by diffusion current. By selecting lateral currents the LPD emitters work in the same configuration as photoconductive antennas while only requiring a metallic boundary near photo-excitation. We investigate the mechanism of the photo-Dember effect and the suppression that causes the LPD effect. Both 1D and 2D models are demonstrated to for calculating diffusion currents within semiconductors and are used within finite element modelling to demonstrate dipole suppression. Optical fluence, beam position and polarisation are characterised within GaAs LPD emitters with SI-GaAs showing a competing generation mechanism from the Schottky barrier at high fluences. We find that the emitter dependence on optical polarisation is due to plasmonic enhancement that occurs on the metal boundary. We demonstrate a simple to fabricate multiplexed LPD emitter based on metals with different reflectivities within the terahertz regime that can be scaled over a large area and propose a design using plasmonic enhancement. |
|---|