Temperature Dependent Carrier Transport in Hydrogenated Amorphous Semiconductors for Thin Film Memristive Applications

This paper demonstrates the transport of electron and hole carriers in two distinct hydrogenated amorphous semiconductor materials at different temperatures. Compared to crystalline materials, the amorphous semiconductors differ structurally, optically and electrically, hence the nature of carrier transport through such amorphous materials differ. Materials like hydrogenated amorphous silicon and amorphous IGZO have been used for the study of temperature dependent carrier transport in this paper. Simulation results have been presented to show the variation of free electron and hole concentration, trapped electron and hole concentration with energy at 300K for both the materials. The change in mobility with a change in the Fermi level has been plotted for different temperatures. The effect of temperature on Brownian motion mobility of electrons and holes in hydrogenated amorphous silicon and amorphous IGZO has been demonstrated towards the end of this paper.

A phenomenological approach to anomalous transport in complex or disordered media

We aim to derive a phenomenological approach to link the theories of anomalous transport governed by fractional calculus and stochastic theory with the conductivity behavior governed by the semi-empirical conductivity formalism involving Debye, Cole-Cole, Cole-Davidson, and Havriliak-Negami type conductivity equations. We want to determine the anomalous transport processes in the amorphous semiconductors and insulators by developing a theoretical approach over some mathematical instruments and methods. In this paper, we obtain an analytical expression for the average behavior of conductivity in complex or disordered media via using the fractional-stochastic differential equation, the Fourier-Laplace transform, some natural boundary-initial conditions, and familiar physical relations. We start with the stochastic equation of motion called the Langevin equation, develop its equivalent master equation called Klein-Kramers or Fokker-Planck equation, and consider the time-fractional generalization of the master equation. Once we derive the fractional master equation, then determine the expressions for the mean value of the variables or observables through some calculations and conditions. Finally, we use these expressions in the current density relation to obtain the average conductivity behavior.

A Transient Analysis for Amorphous Photoconductors

The study has been carried out for the transient response of photosensors fabricated by amorphous semiconductors under variable levels of excitation when switched off from steady-state. The curves for the entire range of the transient have been plotted in the terms of photoconductivity and they can be converted to current decay curves by multiplying with the applied electric field and the cross-sectional area of the sample. For this purpose, in the calculations, the transit time effect is included. Also, the switching time and gain of the photoconductor have been calculated. It is found that the current gain of the device increases as the density of thermal equilibrium electrons is made higher, compared to that of holes by moving the Fermi level upward. However, this also increased the switching time and its performance, as a switch becomes poorer.

Simulation and Theory of Classical Spin Hopping on a Lattice

The behavior of spin for incoherently hopping carriers is critical to understand in a variety of systems such as organic semiconductors, amorphous semiconductors, and muon-implanted materials. This work specifically examined the spin relaxation of hopping spin/charge carriers through a cubic lattice in the presence of varying degrees of energy disorder when the carrier spin is treated classically and random spin rotations are suffered during the hopping process (to mimic spin–orbit coupling effects) instead of during the wait time period (which would be more appropriate for hyperfine coupling). The problem was studied under a variety of different assumptions regarding the hopping rates and the random local fields. In some cases, analytic solutions for the spin relaxation rate were obtained. In all the models, we found that exponentially distributed energy disorder led to a drastic reduction in spin polarization losses that fell nonexponentially.