Browsing by Author "Stephen, A."

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    Impact ionisation electroluminescence in planar GaAs-based heterostructure gunn diodes: spatial distribution and impact of doping non-uniformities
    (American Institute of Physics, 2013-03-27) Stephen, A.; Khalid, A.; Cumming, D. R. S.; Oxley, C. H.; Glover, James; Kuball, M.; Montes, Miguel; Dunn, G.
    When biased on the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. This EL forms non-uniform patterns whose intensity shows short-range intensity variations in the direction parallel to the contacts and decreases along the device channel towards the cathode. This paper employs Monte Carlo models, in conjunction with the experimental data, to analyse these non-uniform EL patterns and to study the carrier dynamics responsible for them. It is found that the short-range lateral (i.e. parallel to the device contacts) EL patterns are probably due to non-uniformities in the doping of the anode contact, hence demonstrating the usefulness of EL analysis on the detection of such inhomogeneities. The overall decreasing EL intensity towards the anode is also discussed in terms of the interaction of holes with the time-dependent electric field due to the transit of the Gunn domains. Due to their lower relative mobility and to the low electric field outside of the Gunn domain, freshly generated holes remain close to the anode until the arrival of a new domain accelerates them towards the cathode. This results, when averaged over several Gunn domain transits, on a higher hole density, and hence a higher EL intensity, next to the anode.
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    Improvements in thermionic cooling through engineering of the heterostructure interface using Monte Carlo simulations
    (AIP Publishing, 2013-07-30) Stephen, A.; Dunn, G. M.; Oxley, C. H.; Glover, James; Montes, Miguel; Cumming, D. R. S.; Khalid, A.; Kuball, M.
    A self-consistent Ensemble Monte Carlo (EMC) model was developed to simulate the thermionic effect in heterostructure barrier coolers. The model was validated on an InGaAs-InGaAsP heterostructure device of variable barrier height and width, producing good quantitative agreement with previous literature results. The operation of the cooler was found to be a complex and intricate process depending on the field, conduction band and details of barrier structure. When applied to a GaAs-AlGaAs micro-cooler there was good agreement with the experimental results. Importantly, very small alterations in the barrier structure were found to lead to considerable changes in device performance
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    In0.53Ga0.47As Planar Gunn Diodes Operating at a Fundamental Frequency of 164 GHz
    (IEEE, 2013) Khalid, A.; Li, C.; Papageogiou, V.; Dunn, G. M.; Steer, M. J.; Thayne, I. G,; Kuball, M.; Oxley, C. H.; Montes, Miguel; Stephen, A.; Glover, James; Cumming, D. R. S.
    We present the first results of a planar Gunn diode made in In0.53Ga0.47As on an InP substrate, operating at a fundamental frequency up to 164 GHz. For a 120-μm-wide device with a 1.3-μm active channel length, the highest power achieved was approximately −10 dBm at 164 GHz.
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    Micro-cooler enhancements by barrier interface analysis
    (AIP Publishing, 2014) Stephen, A.; Dunn, G. M.; Glover, James; Oxley, C. H.; Bajo, M. M.; Cumming, D. R. S.; Khalid, A.; Kuball, M.
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    Micro-coolers fabricated as a component in an integrated circuit
    (IOP Publishing, 2014-12) Glover, James; Khalid, A.; Stephen, A.; Dunn, G.; Cumming, D.; Oxley, C. H.
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    Novel Infra-Red (IR) Thermal Measurements on GaAs Micro-coolers
    (2012-11) Glover, James; Hopper, R.; Maricar, M.; Khalid, A.; Cumming, D.; Montes, Miguel; Kuball, M.; Dunn, G.; Stephen, A.; Oxley, C. H.
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    Reduction of impact ionization in GaAs-Based Planar Gunn Diodes by Anode Contact Design
    (IEEE, 2012) Montes, Miguel; Dunn, G.; Stephen, A.; Khalid, A.; Li, C.; Cumming, D.; Oxley, C. H.; Hopper, Richard; Kuball, M.
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    Terahertz oscillations in an In0.53Ga0.47As submicron planar Gunn diode
    (AIP Publishing, 2014) Khalid, A.; Dunn, G. M.; Macpherson, R. F.; Thoms, S.; Macintyre, D.; Li, C.; Steer, M. J.; Papageorgiou, V.; Thayne, I. G,; Kuball, M.; Oxley, C. H.; Montes Bajo, M.; Stephen, A.; Glover, James; Cumming, D. R. S.