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Semiconductors
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
In Fig. 2.11 we show the electron drift velocity as a function of electric field for a number of semiconductors. The linear dependence at small fields illustrates the low field mobility, with GaAs having a larger low-field mobility than silicon and hence a proportionally larger drift velocity. We also note that the function does indeed saturate for Si and Ge, but with Group III-V materials, the high-field behaviour of the drift velocity does not follow this pattern. Instead, the drift velocity reaches a peak and then starts to decrease. This is because the band structure in these materials contains more than one local minima in the conduction band (see Section 2.3.5.3). If we take GaAs as an example, under normal low field conditions, carrier dynamics are dominated by transitions to and from the Γ valley (see Fig. 2.7). This minimum has a lower effective mass than the other two valleys and therefore a higher mobility. However, as the electric field increases beyond ~3 kV cm−1, some of the conduction electrons that normally occupy the Γ band will have enough energy to occupy energies in the second minima (L band) with its higher effective mass and lower mobility. The minima occur at the edge of the Brillouin zone at an energy of ~0.3 eV higher than the Γ valley minimum. As the field is increased further, the proportion of electrons with the lower mobility increases and the drift-velocity will continue to decrease until all the electrons share the lower mobility and the drift velocity levels off. This effect was first suggested by Ridley and Watkins [34], and it forms the operational basis of the Gunn diode [35] used extensively for microwave applications.
Oscillators and Signal Sources
Published in J. C. G. Lesurf, Millimetre-wave Optics, Devices and Systems, 2017
The Gunn diode (or transferred-electron device) offers a much higher level of device reliability, and a generally lower level of sideband noise. The only significant disadvantage of the Gunn device compared with the impatt is a lower continuous power level. The device operates by exploiting an effect observed by J B Gunn.
Conformational stability of cyclopropanecarboxaldehyde is ruled by vibrational effects
Published in Molecular Physics, 2021
Silvia Alessandrini, Mattia Melosso, Ningjing Jiang, Luca Bizzocchi, Luca Dore, Cristina Puzzarini
The rotational spectrum of CPCA has been recorded between 246 and 294 GHz with a frequency-modulation millimetre spectrometer, described in details elsewhere [22,23]. In the current work, the spectrometer was equipped with a Gunn diode (J.E. Carlstrom Co., 80–115 GHz) coupled to a Virginia Diodes wide-band tripler (WR3.4x3, 220–330 GHz) as primary source of radiation. The phase and frequency stability of the radiation is governed by a phase-lock loop, in which the Gunn diode radiation is mixed with a local oscillator and their frequency difference is compared with a 75 MHz reference signal produced by a synthesiser (HP8642A). The latter also provides the frequency modulation of the output radiation at f = 48 kHz.
A study on angular distribution of THz radiation driven by two-colour laser-induced microplasma
Published in Journal of Modern Optics, 2023
Abolfazl Yousef-Zamanian, Mohammad Neshat
Terahertz (THz) radiation has been widely used in spectroscopy and imaging applications [1–3]. For most applications in imaging, a narrow band radiation generated by e.g. photomixing, Gunn diode, or quantum cascade lasers (QCL) might be adequate [2,4]. However, THz spectroscopy demands a broadband source. This is because in the entire THz spectrum, there are distinct spectroscopic fingerprints for the crystalline lattice vibrations (phonon modes), hydrogen-bonding stretches and other intermolecular vibrations of molecules in many chemical and biological materials [4].
EPR study of the polydomain structure of the twist-bend nematic phase of CB9CB in the bulk
Published in Liquid Crystals, 2018
Corrado Bacchiocchi, Maria-Gabriela Tamba, Georg H. Mehl, Alberto Arcioni, Isabella Miglioli, Claudio Zannoni
Samples of CSL-doped CB9CB were inserted into glass capillaries of 1.8 mm internal diameter for the EPR measurements. EPR spectra were acquired with a Bruker EMX spectrometer equipped with an ER 041XG microwave X-band (9.5 GHz) Gunn Diode bridge and a rectangular ER 4102ST cavity. The samples were thermostated with a nitrogen flux through a variable temperature unit Bruker B-VT 2000. The temperature was monitored with a calibrated type T thermocouple (Comark Ltd.) kept in close proximity with the sample and showed a stability better than 0.05 K.