Chowdhury, S

Davies, AG

Dean, P

Freeman, JR

Kumar, M

Li, L

Linfield, EH

Mohandas, RA

Rosamond, MC

White Rose Research Online

This is a repository copy of Study of the effect of annealing temperature on low-temperature-grown-GaAs photomixers.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/88249/Version: Accepted VersionConference or Workshop Item:Chowdhury, S, Freeman, JR, Rosamond, MC et al. (6 more authors) (2015) Study of the effect of annealing temperature on low-temperature-grown-GaAs photomixers. In: UK Semiconductors 2015, 01-02 Jul 2015, Sheffield, UK. eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Study of the effect of annealing temperature on low-temperature-grown-GaAs photomixers Siddhant Chowdhury,* Joshua R. Freeman, Mark C. Rosamond, Reshma A. Mohandas, Manoj Kumar, Lianhe Li, Paul Dean, A. Giles Davies and Edmund H. Linfield School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, U.K. *el08s2c@leeds.ac.uk Introduction Photomixers are compact sources of continuous-wave (cw) terahertz (THz) radiation that operate at room temperature. Compared to pulsed excitation schemes commonly used in terahertz time domain spectroscopy, narrowband THz generation using cw excitation  provides several advantages – namely, better frequency resolution, higher spectral power density, and the possibility of frequency tuning [1, 2]. We present a systematic study of the effect of annealing temperature on the performance of photomixers fabricated on LT-GaAs substrates, with a broadband log-spiral antenna and interdigitated electrode design.  The measured emission bandwidths are understood in terms of the material resistivity and carrier lifetime, measured using a photo-correlation technique. Methodology and Results LT-GaAs films were epitaxially grown by molecular-beam epitaxy on semi-insulating GaAs substrates and annealed ex-situ at temperatures between 500-625 °C. Ti/Au (10 nm/ 150 nm) was patterned, using electron-beam lithography, evaporation and lift-off, on the substrates to form three pairs of interdigitated electrodes (0.2 µm wide with a 1.6 µm gap), centred in a three-turn self-complimentary broadband log-spiral antenna. The photomixers were characterised by heterodyne excitation using two commercially available, fiber-coupled, frequency tuneable cw diode lasers operating at ~780 nm. The generated radiation was collected and focused on a GaAs-based TOPTICA Photonics photomixing receiver using a hyper-hemispherical silicon lens and two parabolic mirrors. The bandwidth of the emitters was found to vary with annealing temperature due to changes in resistivity and carrier-lifetime of the material. Both the resistivity and carrier-lifetime increased with increasing annealing temperature. With increasing resistivity, a reduction in background noise lead to improved bandwidth but this was countered by an increase in carrier lifetime that acted to reduce the bandwidth. As such, the annealing temperature needs to be optimised to give high material resistivity and low carrier-lifetime for good CW performance. In this study, samples annealed at 575 °C were found to generate the highest bandwidths >1.9 THz, as shown in Fig. 1.  In addition, photo-correlation measurements revealed a corresponding photo-correlation lifetime of 1.08 ps, as also shown in Fig. 1. 1. Preu, S., et al., Tunable, continuous-wave Terahertz photomixer sources and applications. Journal of Applied Physics, 2011. 109(6): p. 061301. 2. Verghese, S., et al., Generation and detection of coherent terahertz waves using two photomixers. Applied Physics Letters, 1998. 73(26): p. 3824-6. Fig 1: Comparison of bandwidth and photo-correlation lifetime of LT-GaAs photomixer at different annealing temperatures. (Inset) Heterodyne frequency response of two photomixers, annealed at 500 °C and 575 °C. 

Study of the effect of annealing temperature on low-temperature-grown-GaAs photomixers

https://eprints.whiterose.ac.uk/88249/1/UK%20Semiconductors%202015%20-%20Siddhant%20Chowdhury.pdf

Study of the effect of annealing temperature on low-temperature-grown-GaAs photomixers

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