Experimental and numerical investigation of Poole-Frenkel effect on dynamic R ON transients in C-doped p-GaN HEMTs

In this paper, we investigate the influence of Poole-Frenkel Effect (PFE) on the dynamic R ON transients in C-doped p-GaN HEMTs. To this aim, we perform a characterization of the dynamic R ON transients acquired during OFF-state stress (i.e., V GS,STR = 0 V < V T, V DS,STR = 25–125 V and we interpret the results with the aid of numerical simulations. We find that dynamic R ON transients at room temperature accelerate with V DS,STR 1/2, which is signature of PFE, as further confirmed by the simultaneous decrease of the activation energy (E A) extracted from the Arrhenius plot of the dynamic R ON transients at V DS,STR = 50 V and T = 30–110 °C. Results obtained by means of calibrated numerical simulations reproduce the exponential dependence of transients time constants (τ) on V DS,STR 1/2 and consequent E A reduction only when including PFE enhancement of hole emission from dominant acceptor traps in the buffer related to C doping. This result is consistent with the model that considers hole emission from acceptor traps (rather than electron capture) as the mechanism underlying dynamic R ON increase during OFF-state stress.

THERMO-FIELD PULA-FRENKEL EFFECT IN TlFeS2 CRYSTALS

Based on the study of the dependence (, it was shown that the current in the nonlinear region (taking into account the thermal-field effect of Poole-Frenkel) is due to a weak field effect, both when measured in parallel and perpendicular to the crystallographic axis crystal TlFeS2. The calculated values of the concentration of ionized centers Nt, the mean free path λ, and the values of the Frenkel coefficient in the shape of a potential well in TlFeS2 crystals have been determined.

Significantly Improved Electrical Properties of Crosslinked Polyethylene Modified by UV-Initiated Grafting MAH

Direct current (DC) electrical performances of crosslinked polyethylene (XLPE) have been evidently improved by developing graft modification technique with ultraviolet (UV) photon-initiation. Maleic anhydride (MAH) molecules with characteristic cyclic anhydride were successfully grafted to polyethylene molecules under UV irradiation, which can be efficiently realized in industrial cable production. The complying laws of electrical current varying with electric field and the Weibull statistics of dielectric breakdown strength at altered temperature for cable operation were analyzed to study the underlying mechanism of improving electrical insulation performances. Compared with pure XLPE, the appreciably decreased electrical conductivity and enhanced breakdown strength were achieved in XLPE-graft-MAH. The critical electric fields of the electrical conduction altering from ohm conductance to trap-limited mechanism significantly decrease with the increased testing temperature, which, however, can be remarkably raised by grafting MAH. At elevated temperatures, the dominant carrier transport mechanism of pure XLPE alters from Poole–Frenkel effect to Schottky injection, while and XLPE-graft-MAH materials persist in the electrical conductance dominated by Poole–Frenkel effect. The polar group of grafted MAH renders deep traps for charge carriers in XLPE-graft-MAH, and accordingly elevate the charge injection barrier and reduce charge mobility, resulting in the suppression of DC electrical conductance and the remarkable amelioration of insulation strength. The well agreement of experimental results with the quantum mechanics calculations suggests a prospective strategy of UV initiation for polar-molecule-grafting modification in the development of high-voltage DC cable materials.

Прогнозирование величины захваченного заряда в захороненном оксиде кремния структур кремний-на-изоляторе с применением эффекта Пула-Френкеля

The opportunity to predict trapped charge value in buried silicon oxide of silicon-on-insulator structures using Poole−Frenkel effect was investigated. Using measuring and modeling of current–voltage characteristics of buried silicon oxide at different temperatures conditions for Poole−Frenkel effect in this layer were determined. Processes taking place in buried oxide during measurement of current–voltage characteristics and annealing were considered. Conditions of thermal field treatment of buried oxide for radiation exposure imitation using injection were determined. Dependence of accumulated positive charge value in buried silicon oxide as a result of injection on Poole−Frenkel current value was estimated. The opportunity to use Poole−Frenkel effect for buried oxide defectiveness evaluation during manufacturing of microcircuits with enhanced dose radiation hardness is shown.

Влияние электрического поля на энергию активации локальных уровней в полупроводниках со слоистой (GaSe) и кубической структурой (Ga-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=-)

The results of measuring the electrical conductivity of layered crystals (GaSe, GaTe, and their solid solutions) and cubic crystals (Ga_2Se_3) in strong electric fields (up to 5 × 10^5 V/cm) in the temperature range of 77–300 K are presented. These results are compared with predictions of the phenomenological theory of concentration instability in semiconductors. This theory considers the role of the Frenkel effect, which is related to the thermionic ionization of traps causing instability in semiconductors with an S -shaped current–voltage ( I – V ) characteristic. Based on the results of measuring the electrical conductivity of layered and cubic crystals exhibiting the Frenkel effect and described by the theory of current instability in semiconductors, the free-carrier concentration in the aforementioned types of chalcogenide semiconductors is estimated to be n = (3 × 10^13–4 × 10^15) cm^–3.