The Gunn effect

Butcher, P N

doi:10.1088/0034-4885/30/1/303

Cited by 149 publications

(54 citation statements)

References 76 publications

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“…A second possible application of hot carriers generation are Gunn diodes. In III/V semiconductors, a microwave signal of high frequency appears if the applied bias field exceeds a threshold value 34 . This effect arises when the high electrical field promotes electrons from the conduction band minimum to an upper valley 34,35 .…”

Section: Pacs Numbersmentioning

confidence: 99%

Ultrafast electron dynamics reveal the high potential of InSe for hot-carrier optoelectronics

et al. 2018

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We monitor the dynamics of hot carriers in InSe by means of two photons photoelectron spectroscopy (2PPE). The electrons excited by photons of 3.12 eV experience a manifold relaxation. First, they thermalize to the electronic states degenerate with theM valley. Subsequently, the electronic cooling is dictated by Fröhlich coupling with phonons of small momentum transfer. Ab-initio calculations predict cooling rates that are in good agreement with the observed dynamics. We argue that electrons accumulating in states degenerate with theM valley could travel through a multilayer flake of InSe with lateral size of 1 micrometer. The hot carriers pave a viable route to the realization of below-bandgap photodiodes and Gunn oscillators. Our results indicate that these technologies may find a natural implementation in future devices based on layered chalcogenides. PACS numbers:Van der Waals chalcogenides display a variety of different specifics that depend on their composition and number of layers. The weak mechanical binding of the atoms along the stacking direction facilitates the realization of heterostructures with different functionalities. Some recent achievements have been: the fine tuning of the band gap 1-3 , the control of valley polarization 4 and the realization of devices with high mobility 5-7 . In this context, InSe is one of the building blocks with the highest potentials.The bulk crystals of InSe can be thinned down to a few layers and encapsulated in hBN 7 . By these means, Bandurin and collaborators have fabricated transitors whose quality is high enough to observe Shubnikovde Haas oscillations and quantum Hall effect 7 . These results point out the two aspects making InSe particularly appealing. On one hand, the mobility of charge carriers rivals with the one measured in graphene 8 . On the other hand, the bulk band gap of 1.26 eV, is ideally suited for optoelectronic devices. Indeed, several groups have recently reported that InSe 10,11 and InSegraphene heterostructures 12 have excellent photoresponsivity in the visible spectral region. Such photodetectors could be patterned on a large scale over flexible supports 13 . Eventually, the application of larger bias can drive the photodetector in the avalanche regime 14 .The conception of devices based on InSe would greatly profit from a precise knowledge of the transient state following photoexcitation. Some pioneering experiments have investigated the coherent propagation and dephasing of the exciton-polariton 15,16 . These optical meth-ods revealed a beating polarization induced by resonant pulses, but provided no insights on the energy relaxation of hot carriers. Here, we address this issue by mapping the dynamics of excited electrons in reciprocal space 17,18 . Our two photon photoemission (2PPE) data show that photoexcitation above theM valley results in a high density of electrons with excess energy of ∼ = 0.6 eV and cooling time of 2 ps. First principle calculations of the electron-phonon coupling discriminate between the distinct scattering mechani...

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Section: Pacs Numbersmentioning

confidence: 99%

Ultrafast electron dynamics reveal the high potential of InSe for hot-carrier optoelectronics

et al. 2018

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“…It is well known [19,20] that the static v-F characteristics which were calculated within the HD approach remain valid even in the situations when the HD model is physically inapplicable, e.g. at very low electron densities.…”

Section: Resultsmentioning

confidence: 99%

“…Although this peculiar property of the HD model has not been explained or proved so far, most likely it has something to do with the shape of non-equilibrium distribution functions used (the Maxwell-Boltzmann or Fermi functions, which differ from the equilibrium distributions by substitution of the lattice temperature by the electron temperature). Note that it is more difficult to justify the use of the displaced Maxwellian or Fermi functions [19] which are described by two parameters - the electron temperature and the drift wave vector, as this requires a complete e-e control of the energy and momentum relaxation. This is practically impossible to achieve in bulk semiconductors since the required high doping in order to obtain high carrier density also results in high electron momentum scattering rates by the doping impurities, i.e.…”

Section: Resultsmentioning

confidence: 99%

Overshoot mechanism in transient excitation of THz and Gunn oscillations in wide-bandgap semiconductors

2012

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A detailed study of high-field transient and direct-current (DC) transport in GaN-based Gunn diode oscillators is carried out using the commercial simulator Sentaurus Device. Applicability of drift-diffusion (DD) and hydrodynamic (HD) models to high-speed, high-frequency devices is discussed in depth, and the results of the simulations from these models are compared. It is shown, for a highly homogeneous device based on a short (2 μm) supercritically doped (1017 cm−3) GaN specimen, that the DD model is unable to correctly take into account some essential physical effects which determine the operation mode of the device. At the same time, the HD model is ideally suited to solve such problems due to its ability to incorporate non-local effects. We show that the velocity overshoot near the device contacts and space charge injection and extraction play a crucial role in defining the operation mode of highly homogeneous short diodes in both the transient regime and the voltage-controlled oscillation regime. The transient conduction current responses are fundamentally different in the DD and HD models. The DD current simply repeats the velocity-field (v-F) characteristics, and the sample remains in a completely homogeneous state. In the HD model, the transient current pulse with a full width at half maximum of approximately 0.2 ps is increased about twofold due to the carrier injection (extraction) into (from) the active region and the velocity overshoot. The electron gas is characterized by highly inhomogeneous distributions of the carrier density, the electric field and the electron temperature. The simulation of the DC steady states of the diodes also shows very different results for the two models. The HD model shows the trapped stable anodic domain in the device, while the DD model completely retains all features of the v-F characteristics in a homogeneous gas. Simulation of the voltage-controlled oscillator shows that it operates in the accumulation layer mode generating microwave signals at 0.3 to 0.7 THz. In spite of the fact that the known criterion of a Gunn domain mode n0L > (n0L)0 was satisfied, no Gunn domains were observed. The explanation of this phenomenon is given.

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“…To begin with, we assume a two-valley model for the conduction band [28] , one having a heavier effective mass for the electrons than the other of the two valleys. Consequently, electrons move faster in the lower mass valley which is also lower in energy.…”

Section: Bi Current Instability In a Semiconductormentioning

confidence: 99%

Connection between Extended Thermodynamics and Transport Theory

Eu¹

1986

Journal of Non-Equilibrium Thermodynamics

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Based on the formalism provided by the modified moment method for the Boltzmann equation and the generalized Boltzmann equation and on the axiomatic formalism of irreversible thermodynamics of fluids, we discuss the connection of extended irreversible thermodynamics with transport processes. It is shown how the entropy surface can be constructed from the experimental information on transport processes and vice versa. IntroductionIn macroscopic phydics and physical chemistry a process is meant by a series of physical events progressing in space-time under initial and boundary conditions. When matter and energy are transported within the system and across the boundaries of the system owing to physical causes, we call the processes the transport processes of matter and energy, or simply the transport processes. Since all natural macroscopic processes are clearly subject to the thermodynamic laws, the transport processes in fluids and solids must equally conform to the requirements by the thermodynamic laws. Since transport processes are generally time-and space-dependent, the equilibrium thermodynamics formalism is obviously inadequate for proper macroscopic description of them and the formalism must be so generalized as to adequately deal with them, hopefully, to any degree of nonequilibrium. If the processes occur in a state of the system near equilibrium the linear irreversible thermodynamic formalism [1] developed by many pioneers is adequate and provides a powerful and general theory of transport processes. The theory is described in numerous monographs on linear irreversible thermodynamics. In the linear theory the fluxes characterizing the transport processes are linearly dependent on the thermodynamic forces; hence the term linear. However, many processes in nature occur in a state removed far from equilibrium, and linear flux-force relationships are no longer adequate. There now arises the necessity to formulate a theory to deal with situations that gener-J. ally require, for example, nonlinear flux-force relationships or their suitable generalizations. Transport processes requiring nonlinear flux equations will be termed nonlinear transport processes, and the corresponding thermodynamics nonlinear irreversible thermodynamics. Nonlinear problems are generally rather individual-looking in their superficial appearance, yet as is recognized through numerous, mathematical, physical and chemical investigations [2] on the problems, they appear to share some important characteristic features that seem to be common to all of them. What we wish to discuss here is the irrversible thermodynamics aspects underlying nonlinear transport processes in fluids and solids. Since the mathematical structure of nonlinear irreversible thermodynamics is difficult to guess on purely phenomenological grounds for obvious reasons, we rely on kinetic theories such as the Boltzmann kinetic theory [3] to guide us in exploring for a possible structure of such a theory. The mathematical framework so acquired in the kinetic theory approach ...

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The Gunn effect

Cited by 149 publications

References 76 publications

Ultrafast electron dynamics reveal the high potential of InSe for hot-carrier optoelectronics

Ultrafast electron dynamics reveal the high potential of InSe for hot-carrier optoelectronics

Overshoot mechanism in transient excitation of THz and Gunn oscillations in wide-bandgap semiconductors

Connection between Extended Thermodynamics and Transport Theory

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