Hot-electron Transport In Semiconductors Research Articles

Negative Differential Conductivity in Gases: The “True Origin”

In a recent article [Yamamoto and Ikuta: J. Phys. Soc. Jpn. 68 (1999) 2602] state that the true origin of negative differential conductivity (NDC) has never been shown, in apparent contradiction of claims made in earlier papers [Z. Lj et al. .: Aust. J. Phys. 37 (1984) 23; R. E. Robson: ibid. 37 (1984) 35]. In the present paper, we argue that the true origin of NDC has indeed been explained satisfactorily, and present a comprehensive range of calculations for a number of cases, demonstrating the effectiveness of momentum transfer theory [ Hot electron transport in semiconductors (Springer, Berlin, 1985) p. 82] for understanding NDC from both a qualitative and quantitative perspective.

Balance-equation approach to hot-electron transport in semiconductors irradiated by an intense terahertz field

We investigate the effect of a uniform intense terahertz radiation on hot-electron transport in semiconductors driven by a dc or slowly varying electric field of arbitrary strength. Using a vector potential for the high-frequency field and a scalar potential for the dc or slowly varying field, we are able to separate the center-of-mass motion from relative motion of electrons and to distinguish the slowly varying part from the rapidly oscillating part of the center-of-mass velocity. Considering the fact that relevant transport quantities are measured over a time interval much longer than the period of the terahertz radiation field, we obtain a set of momentum and energy balance equations, without invoking a perturbational treatment of the electron-photon interaction. These equations, which include all the multiphoton processes, are applied to the examination of hot-carrier transport in a GaAs-based quantum well subjected to a weak or a strong dc bias and irradiated by a terahertz radiation of various frequency and strength in both the parallel and vertical configurations. Up to as many as |n|=50 absorption and emission multiphoton channels are included in the numerical calculation. The present approach turns out to be a very convenient and efficient tool to study the effect of an intense high-frequency radiation on dc or slowly varying carrier transport in semiconductors. Its applicable frequency range and its connection with previously developed balance-equation treatment are discussed.

Efficient ohmic boundary conditions for the Monte Carlo simulation of electron transport

The development of macroscopic transport models, accurate for studying hot-electron transport in semiconductors, involves a direct consideration of higher-moment terms. All hydrodynamic transport models (HTM's), derived from moments of the Boltzmann transport equation, require the introduction of closure relations to terminate the resulting infinite set of macroscopic equations. These closure relations are used as analytical approximations to distributional-dependent integral coefficients. The most popular theoretical approach employed for the construction and evaluation of these higher-moment transport-parameter closures is the Monte Carlo (MC) method. Since the MC method is computationally intensive, the discovery and implementation of efficient MC modeling techniques (either numerical or physical) is of significant value. This paper reports on a relationship between device boundary conditions and the convergence range of higher-moment terms in time-independent MC simulations. Specifically, a set of ohmic BC's which offer computational advantages is presented. This particular mathematical approach, which allows for two degrees of freedom, is shown to be more efficient in generating the full electron distribution function than conventional BC methods (i.e., strictly equilibrium-based).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-resolution energy analysis of field-assisted photoemission: A spectroscopic image of hot-electron transport in semiconductors.

Hot-electron transport in indium phosphide is studied by means of energy-resolved field-assisted photoemission of an Ag/InP Schottky diode. The work function of the thin silver top layer is lowered by cesium and oxygen coadsorption. A quasimonoenergetic electron distribution is created close to the bottom of the conduction band in the bulk of the weakly doped p-type InP crystal by near-band-gap light excitation. The energy-distribution curves of the photoemitted electrons are measured for different values of the bias applied to the Ag/InP contact. It is demonstrated that this set of photoemission spectra constitutes a direct measurement of the evolution of the initial distribution during transport in the high electric field of the band-bending region. From this spectroscopic image of the complex multivalley transport, the relevant energy and momentum relaxation processes are clearly identified. Simple models based on the energy balance between the gain in the electric field and the losses by phonon emission account remarkably well for the experimental results. From the comparison between theory and experiment, the characteristic phonon-scattering times are deduced throughout the first conduction band.

NONEQUILIBRIUM STATISTICAL OPERATOR IN HOT-ELECTRON TRANSPORT THEORY

The Nonequilibrium Statistical Operator method developed by Zubarev is generalized and applied to the study of hot-electron transport in semiconductors. The steady-state balance equations for momentum and energy are derived to the lowest order in the electron-lattice coupling. We show that the derived balance equations are exactly the same as those obtained by Lei and Ting. This equivalence stems from the fact that to the linear order in the electron-lattice coupling, two statistical density matrices have identical effect when they are used to calculate the average value of a dynamical operator. The application to the steady-state and transient hot-electron transport in multivalley semiconductors is also discussed.

Novel photoemission approach to hot-electron transport in semiconductors.

We have performed high-resolution energy analysis of the near-band-gap photoemission of a p-type InP/Ag Schottky diode under electrical bias. This original technique brings direct information on high-electric-field electron transport in semiconductors. From our experimental data, using simple models, we estimate characteristic phonon emission times in an energy range which spans the whole first conduction band, and we evidence an efficient ${\mathrm{\ensuremath{\Gamma}}}_{6}$-${\mathit{X}}_{6}$ intervalley transfer.

Hot electron transport in semiconductors

A recently derived model for stationary flow of energy and charge carriers in semiconductors—consisting of a coupled system of nonlinear elliptic equations—is analysed by the methods of singular perturbation theory. This analysis reveals the solution structure and justifies a modified version of the standard drift-diffusion approximation for charge carrier flow.

Quantum corrections to the Monte Carlo solution of hot-electron transport in semiconductors

By using the Generalized Kadanoff-Baym method, we construct a computational scheme which can be readly included in an ensemble Monte Carlo program to give quantitative estimates of the intra-collisional field effect and/or of collisional broadening. The central quantity in our theory is the joint spectral density K(k,k') which describes the relation between the initial and final kinetic momenta in a scattering event.

Green's-function approach to transient hot-electron transport in semiconductors under a uniform electric field.

Green's-function approach to transient hot-electron transport in semiconductors under a uniform electric field.

Effect of a perturbed acoustic-phonon distribution on hot-electron transport: A Monte Carlo analysis

A Monte Carlo simulation code has been developed to study the effect of phonon perturbations in hot-electron transport in semiconductors. The modifications of carrier drift velocity and mean energy induced by the perturbed acoustic-phonon distribution are studied at low temperatures in p-Ge. Under appropriate conditions, current saturation is obtained as a result of the steady-state phonon perturbation. The Monte Carlo analysis has been complemented and compared with an analytical approach based on a heated and displaced Maxwellian distribution for the electron gas.