SEMINAIRE Département Photonique et Ondes- Groupe TéHO
Plasma Oscillations in a Submicron Planar Gunn Diode
Ata KHALID Research Fellow
MicroSystem Technology Research Group
School of Engineering, University of Glasgow
Jeudi 15 mai 2014, 14 heures
Salle des séminaires, bâtiment 21, 4è étage
The Gunn diode was first demonstrated in 1963 using a GaAs bar-like structure with electrical contacts on its opposing faces . Early research work demonstrated the difficulties of achieving planar structures for several reasons. However, as material quality has continuously improved, new attempts have been made to make Gunn devices in a planar layout that would enable integrated diodes for on chip applications such as high frequency radar and security imaging . Early theoretical investigations show that the high-energy relaxation time of GaAs might limit Gunn oscillation to 60 GHz .
Monte-Carlo simulations showed that ultrafast quasi-ballistic electrons in the Γ-valley would, under the influence of a high electric field caused by an etched recess, achieve a velocity of up to 108 cm/s leading to terahertz operation . Moreover, plasma oscillations up to several THz have been observed in highly doped semiconductor material. InxGa1-xAs displays significant improvements in mobility compared to GaAs with increasing indium content, and Monte-Carlo modelling and experimental data has consequently shown the potential for much higher frequency operation of InxGa1-xAs channel planar Gunn diodes compared to GaAs channel diodes .
In this background of extensive research to develop solid state THz source, I will discuss the development of planar Gunn diode technology and various technology issues needed to be resolved to keep the progress towards a THz source technology. Recent development of submicron planar Gunn diode has shown oscillations above 300GHz for the first time. Agreement with theory and experiment is reasonably good for Gunn oscillations, though with the simulations systematically recording frequencies about 10% higher than those observed experimentally. It was very interesting that Monte Carlo simulations show 450GHz and 688GHz plasma oscillations for our submicron device at lower applied basis, while higher biases were needed in the simulation to maintain accumulation layer Gunn oscillations. There was no plasma oscillation observed during the simulations for devices longer than 750nm. At present we are unable to experimentally verify the predicted plasma wave oscillations due to lack of available experimental set-up. However, it is interesting to note that a 475GHz experimentally measured signal was reported recently in InGaAs channel of a HEMT device .
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