Variable Range Hopping in Hydrogenated Amorphous Silicon-Nickel Alloys (original) (raw)
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Japanese Journal of Applied Physics, 2009
We presented the results of optical and electrical studies of the properties of hydrogenated amorphous silicon (a-Si:H) film which was prepared by hot wire method. Using transmittance measurements, the dielectric constant of the a-Si:H was determined. The temperaturedependent conductivity was measured using the two-point probe method in the temperature range 115-326 K. It was shown that the temperature-dependent conductivity can be well explained by the nearest-neighbor hopping conduction and the Efros-Shklovskii variablerange hopping conduction models. A clear transition from the nearest-neighbor hopping conduction mechanism to the Efros-Shklovskii variable-range hopping conduction mechanism was also observed. The transition between two conduction regimes and characteristic hopping temperatures, as well as the complete set of parameters describing the properties of the localized electrons (the localization length, the hopping energy, the hopping distance, the width of the Coulomb gap, and the value of the density of states at the Fermi level) were determined.
Journal of Physics: Condensed Matter, 2006
Numerical simulation of the steady state photoconductivity in hydrogenated amorphous silicon over a wide temperature range (25-500 K) is extended, to include previously neglected carrier transitions between localized states. In addition to free carrier capture (emission) transitions into (from) localized states, we include the process of electron hopping in conduction band tail states. Exponential distributions are assumed for both conduction and valence band tail states, while the dangling bond defect distribution is calculated in accordance with the defect pool model. Localized to extended state transitions follow the Simmons and Taylor statistics, and localized to localized state transitions involve electron hopping between nearest neighbour sites. Comparison with simulations in the absence of electron hopping reveals a smooth transition around 110 K, between regions of (high temperature) extended state conduction and (low temperature) hopping conduction. A hopping transport energy level is identified as the peak of the energy distribution of the hopping photocarriers, and shows a temperature dependence in agreement with existing theoretical work.
Physical Chemistry of Interfaces and Nanomaterials XI, 2012
We present results of an experimental study of magnetoresistance phenomenon in an amorphous silicon-nickel alloys a-Si 1-y Ni y :H (where y = 0.23) on the insulating side of the metal-insulator transition (MIT) in presence of magnetic field up to 4.5 T and at very low temperature. The electrical resistivity is found to follow the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2. This behaviour indicates the existence of the Coulomb gap (CG) near the Fermi level.
2001
Carrier dynamics in amorphous a-Si1−xREx (RE=Gd, Y) films has been studied in the doping regime close to the metal-insulator transition by means of infrared spectroscopy. Optical constants throughout the entire intra-gap region (hω < 1 eV) have been found to be anomalously sensitive to changes of temperature and/or magnetic field. The observed behavior is consistent with the model of hopping transport where the interaction of carriers with both the lattice and large core spin of Gd ions is taken into account. 71.30.+h, 71.38.Ht, 72.20.Ee, 78.20.Ls, 78.66.Jg
Electronic transport properties of a-Si:H
AIP Advances, 2022
To investigate the electron transport properties of hydrogenated amorphous silicon (a-Si:H), a series of quantum simulations and electron transport analyses were performed. The target system is a nano-scale junction of a-Si:H with various hydrogen concentrations sandwiched between two metal electrodes. The density functional based tight binding simulation was conducted to obtain the electronic structure, and the non-equilibrium Green’s function method was adopted to evaluate the electron transmission coefficient and the electric current under a bias field. It is confirmed that the hydrogen atoms passivate a part of defects in amorphous silicon, but the remaining defects realize the energy states in the bandgap; the p orbitals of silicon atoms mainly contribute to the electron transmission. The transport behavior is greatly affected by the hydrogen concentration. The interface between a-Si:H and the metal electrodes also influences the transport behavior through changing the spatial ...
The temperature-induced transition from 3d to 1d hopping conduction in porous amorphous
Journal of Physics: Condensed Matter, 1997
We have investigated variable-range hopping conduction in amorphous Si 1−c Mn c (c = 4 and 7 at.%) samples obtained by ion implantation and treatment by anodic etching in HF solution-porous silicon. As temperature is reduced, we find a crossover from the exp[−(T 0 /T ) 1/4 ] Mott form to a simply activated law, exp(− E/kT ). This behaviour is attributed to a temperature-induced transition from 3d to 1d hopping conduction in a network of weakly interconnected silicon quantum 'wires'. The mean diameter of the silicon wires, D = 5-6 nm, was deduced from analysis of the conductivity data and is in agreement with XTEM and STM observations. It was found that the density of states in the porous material is smaller than in the compact material due to broadening of the impurity band caused by lateral confinement in the silicon wires.
Journal of Physics: Condensed Matter, 2004
In this paper we study electron dynamics and transport in models of amorphous silicon and amorphous silicon hydride. By integrating the time-dependent Kohn-Sham equation, we compute the time evolution of electron states near the gap, and study the spatial and spectral diffusion of these states due to lattice motion. We perform these calculations with a view to developing ab initio hopping transport methods. The techniques are implemented with the ab initio local basis code SIESTA, and may be applicable to molecular, biomolecular and other condensed matter systems.
Metal-insulator transition in amorphous Si1-xNix: Evidence for Mott’s minimum metallic conductivity
Physical Review B, 1999
We study the metal-insulator transition in two sets of amorphous Si_{1-x}Ni_x films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, w =
Theory of thermally assisted electron hopping in amorphous solids
Zeitschrift f�r Physik, 1971
Using a kinetic equation for thermally assisted hopping processes a general expression for the conductivity a(co) in disordered systems in terms of the collision operator is derived. The d.c. conductivity is determined by the low lying eigenstates of the collision operator. The eigenvalue equation bears a close analogy to the corresponding problem of atomic vibrations in disordered systems. The calculation of the d.c. conductivity is analogous to the calculation of elastic constants from the dynamical matrix. Using a variational approach for the low lying eigenstates we have found a law in a(0)= const-(To/T)~. The error in the value of T O introduced by our trial function has been calculated and found to be reasonably small.