Evidence for multiple impurity bands in sodium-doped silicon MOSFETs

We report measurements of the temperature-dependent conductivity in a silicon metal-oxide-semiconductor field-effect transistor that contains sodium impurities in the oxide layer. We explain the variation of conductivity in terms of Coulomb interactions that are partially screened by the proximity of the metal gate. The study of the conductivity exponential prefactor and the localization length as a function of gate voltage have allowed us to determine the electronic density of states and has provided arguments for the presence of two distinct bands and a soft gap at low temperature.Comment: 4 pages; 5 figures; Published in PRB Rapid-Communication

High performance n(+)/p and p(+)/n germanium diodes at low-temperature activation annealing

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Overview of T and D-T results in JET with ITER-like wall

In 2021 JET exploited its unique capabilities to operate with T and D–T fuel with an ITER-like Be/W wall (JET-ILW). This second major JET D–T campaign (DTE2), after DTE1 in 1997, represented the culmination of a series of JET enhancements—new fusion diagnostics, new T injection capabilities, refurbishment of the T plant, increased auxiliary heating, in-vessel calibration of 14 MeV neutron yield monitors—as well as significant advances in plasma theory and modelling in the fusion community. DTE2 was complemented by a sequence of isotope physics campaigns encompassing operation in pure tritium at high T-NBI power. Carefully conducted for safe operation with tritium, the new T and D–T experiments used 1 kg of T (vs 100 g in DTE1), yielding the most fusion reactor relevant D–T plasmas to date and expanding our understanding of isotopes and D–T mixture physics. Furthermore, since the JET T and DTE2 campaigns occurred almost 25 years after the last major D–T tokamak experiment, it was also a strategic goal of the European fusion programme to refresh operational experience of a nuclear tokamak to prepare staff for ITER operation. The key physics results of the JET T and DTE2 experiments, carried out within the EUROfusion JET1 work package, are reported in this paper. Progress in the technological exploitation of JET D–T operations, development and validation of nuclear codes, neutronic tools and techniques for ITER operations carried out by EUROfusion (started within the Horizon 2020 Framework Programme and continuing under the Horizon Europe FP) are reported in (Litaudon et al Nucl. Fusion accepted), while JET experience on T and D–T operations is presented in (King et al Nucl. Fusion submitted)

A deep-level transient spectroscopy study of implanted Ge p+n and n+p junctions by Pt-induced crystallization

This paper reports on a Deep-Level Transient Spectroscopy (DLTS) study of ion-implanted Ge n(+)p and p(+)n junctions, subjected to a 350 degrees C anneal after Pt-metallization. It is shown that good quality diodes with acceptable reverse current levels can be achieved, pointing to a successful activation and defect removal, especially for the p(+)n junctions. Nevertheless, DLTS reveals the presence of small concentrations of deep levels, which can be associated with residual ion implantation damage and possibly Pt in-diffusion. In the case of the p(+)n diodes, the thermal activation energy of the leakage current increases from 0.38 eV to 0.45 eV, which could be in line with the annealing of the deep-level traps, observed in DLTS. The situation is more complex for the n(+)p junctions, where the low activation energy points to field-assisted leakage current mechanisms, which can be mediated by the residual implantation damage

Post-metallization annealing and photolithography effects in p-type Ge/Al2O3/Al MOS structures

In this work, the combined effect of negative tone photolithography and post-metallization annealing (PMA) on the electrical behavior of Al/Al2O3/p-Ge MOS structures are investigated. During photoresist development, the exposed upper part of the Al2O3 film weakens due to the reaction with the developer. Subsequent processes of Al deposition and PMA at 350 °C result in alumina thickness reduction. The gate electrode formation seems to involve at least three processes: (a) germanium substrate out-diffusion and accumulation at the top of the alumina layer that takes place during the alumina deposition, (b) alumina destabilization, and (c) germanium diffusion into the deposited Al metal and Al diffusion into the alumina. The overall effect is the reduction of the alumina thickness due to its partial consumption. It is shown that the germanium diffusion depends on the annealing duration, and not on the annealing ambient (inert or forming gas). Although PMA passivates interface traps near the valence band edge, the insulating properties of the stacks are degraded. This degradation appears as a low-level ac loss, attributed to a hopping current that flows through the Al2O3 layer. The results are discussed and compared to recently reported on Pt/Al2O3/p-Ge structures formed and treated under the same conditions

Diffusion of implanted nitrogen in germanium.

In the present work diffusion of implanted nitrogen in germanium is studied as a function of implantation energy and post-implantation annealing temperature. Implantations have been performed at a constant dose and energies leading to the amorphization of the substrate. Nitrogen diffusion in Ge is anomalous (not obeying the 2nd Fick’s law) towards the substrate surface on which an Al2O3 layer has been deposited before annealing for protection. There is evidence that N diffusion in Ge is interstitial- assisted and takes place in the presence of Ge interstitials gradients between the Al2O3/Ge and the former amorphous/crystalline (a/c) interface of the substrate during annealing