Sandro Feliziani

A Monte Carlo study of r- epsilon -hopping transient currents in thin dielectric layers with a macroscopically inhomogeneous spatial distribution of hopping centres

The authors report the results of the Monte Carlo simulation of the time-of-flight experiment for variable-range hopping transport in thin dielectric layers, which are spatially inhomogeneous on the macroscopic scale (i.e. on a scale comparable with the layer thickness). In particular, the total density of hopping centres (with Gaussian distribution in energy) is assumed to change exponentially as a function of the distance from the contacts. The results of simulations performed for various system dilutions, various widths of the Gaussian distribution in energy, and various degrees of the layer spatial nonuniformity are discussed.

r-hopping transient currents in thin dielectric layers with macroscopically non-homogeneous spatial distribution of hopping centres

The work is a contribution to the understanding of transient currents, which are usually discussed in the context of the classical time-of-flight (TOF) experiment. In particular, r-hopping pulse injection transient currents in dielectric layers with a macroscopically nonhomogeneous distribution of hopping centres have been investigated with the aid of the Monte Carlo simulation, according to a new algorithm. Both the shape of the transient currents and the value of the effective TOF are found to depend strongly on the degree of macroscopic variations in the hopping-centre concentration over the layer thickness. For a smooth change in space centre concentration, the transient currents may be described by simple analytical expressions, suitable for the estimation of the spatial distribution of hopping centres from experimental data.

Multiple-trapping transient currents in thin dielectric layers with enhanced trap density in the near-contact regions

The authors present several illustrative multiple-trapping current-time characteristics in thin dielectric layers with enhanced trap concentration in the near-contact regions. Such a spatial trap distribution, for different energy trap distributions, leads to a variety of different non-typical shapes of the characteristics. The results have been obtained with the aid of a Monte Carlo simulation for conditions corresponding to the typical time-of-flight method.

Thermally stimulated current transport peaks in insulating layers with spatially non-homogeneous trap distribution

In the present work the authors have investigated the influence of spatial non-homogeneity of trap distribution on thermally stimulated currents (TSC) due to transport of carriers in insulating layers. It has been assumed that at zero time carriers are generated only in a thin layer near one of the contacts. They have proved that for both non-dispersive and dispersive transport the initial increase of TSC is strongly dependent on the spatial distribution of traps. On the other hand, the dependence of TSC maximum on electric field strength, layer thickness and heating rate, and in the case of dispersive transport also on the final current decay, is almost the same as for a homogeneous trap distribution. The analytical results have been found to agree satisfactorily with the results of Monte Carlo simulation of non-isothermal carrier transport for all the model spatial and energetic trap distributions considered. The possibility of determining spatial trap distribution on the basis of the measured TSC has been discussed.

A Monte Carlo simulation of the time-of-flight experiment in non-uniformly defected thin crystalline layers

In the present paper we report on the results of the Monte Carlo simulation of the time of flight (TOF) experiment for r and r- epsilon hopping transport in highly defected very thin crystalline layers. The defects are considered as localized states, between which a hopping motion of the injected carriers is possible. The total (integrated over energy) density of defects is assumed to be spatially non-uniform on the macroscopic scale, i.e. the scale comparable with the layer thickness. In particular, we consider an exponential dependence of the total density of hopping centres on the distance from the layer contacts. The results of simulations performed for various defect concentrations, various defect distributions in energy, and various degrees of the layer spatial non-uniformity are discussed. It is shown that both r and r- epsilon hopping transient currents measured in the classical TOF experiment are highly sensitive to the spatial macroscopic scale variations of the total centre concentration. The detailed shape of the transients depends in a complicated way on the system dilution, the energetic centre distribution, and the character of the spatial variations of the total centre density. The existence of the spatial non-uniformity of the layer could be recognized experimentally by observation of the qualitative changes of the current shape with increasing temperature, which leads to lower dispersion, and thus more pronounced characteristic features of the x-dependent total centre density, such as a higher polarity dependence, or the appearance of the current maxima or plateaux just before the effective TOF.

Thermally stimulated current transport peaks in insulating layers with spatially non-homogeneous trap distribution. II. Bulk initial carrier generation

In the present paper the authors continue the recent investigations of Tomaszewicz et al on the influence of spatial non-homogeneity of the trap distribution on thermally stimulated currents (TSC) due to transport of carriers in insulating layers. They consider here-in contrast to the previous work-the case of bulk initial generation of carriers. For both non-dispersive and dispersive transport, the analytical formulae obtained agree satisfactorily with the results of Monte Carlo simulation. The possibility of determining the spatial trap distribution on the basis of the measured TSC is discussed.