Nanometer-sized multijunction arrays are expected to exhibit a large Coulomb blockade effect. However, up to now, only highly disordered arrays can be fabricated. In this article, we evaluate the consequences of disorder on the dispersion of the device characteristics. We show that, as observed for regular arrays, the threshold voltage Vth increases with the length of the multijunction array. At very low temperature, the Vth dispersion is small. Conversely, at higher temperature, a large dispersion in Vth is observed. We evidence the importance of the different array parameters with respect to the device characteristics. We show that the crucial parameters are the tunnel resistances and, therefore, for a two-dimensional array, the total resistance of the minimal resistance path is the most relevant parameter.

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We have shown that for a one-dimensional multijunction array with a broad junction length distribution, we can increase the mean threshold voltage Vth for a given maximal tunnel resistance without increasing the scatter of Vth. For two-dimensional arrays we can increase strongly the output of devices which do not behave as open circuits, without any loss on the scatter on Vth, and still increase the latter with respect to a single-island device. The experimental background which justified the calculation will be described, as our model needs the experimental distribution of the island dimensions and junction lengths. Such a result may either show a way to increase the threshold voltages for a given technology, or allow for larger and therefore more controllable dimensions, or even extend the choice of materials.

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The temperature behavior of multiple tunnel junction (MTJ) devices made with sub-5-nm gold islands is investigated. A smooth decrease of the Coulomb gap with increasing temperatures is observed. The critical temperature beyond which the Coulomb blockade effect is suppressed is found to change as a function both of the average size of the islands and of the size of the two-dimensional (2D) array of islands forming the MTJ. This latter property is attributed to the role of disorder in the 2D array. Results are compared with Monte Carlo simulations of current transport through highly disordered 2D arrays which reproduce the experimental evolution of the Coulomb gap with temperature.

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Electron paramagnetic resonance spectra of fast neutron irradiated semi-insulating GaAs, recorded at 9 GHz and 4.2 K, have been studied as a function of isochronal thermal anneals. Their decomposition into quadruplet and singlet allows one to determine the main annealing temperatures of the corresponding defects, previously identified as As4+Ga and V2−Ga, which occur respectively at 400 and 600 °C. Comparison with the behavior of implantation damage shows that electrical activation of Be+ implants is correlated with the annealing of the main defects on the cation sublattice. Finally, the linewidth variation of the quadruplet during its decay indicates a concomitant change of the local environment of the As4+Ga center.

The variation of As+Ga content during illumination in weakly electron-irradiated semi-insulating GaAs is analyzed in terms of the pertinent parameters of the midgap donor EL2, leading to a determination of the total content of photoquenchable anion antisites independent of initial paramagnetic fraction. The associated photocarrier release is used for modeling the corresponding variation of the concentration of neutralized ST1 acceptors in a scheme involving one donor and two competing acceptor levels.