Temperature activated conductivity of Ge₂Sb₂Te₅: connection to the variation of Fermi level and implications on resistance drift

Abstract

The non-Arrhenius behaviour of Ge2Sb2Te5 conductivity is attributed to the non-linear temperature dependence of the Fermi level, assuming extended state conduction by free holes. The temperature-dependent Fermi level is shown to alter values of activation energy and prefactor for conductivity so that their exact determination becomes impossible using the conductivity data alone. However, if one assumes the temperature dependence of the Fermi level to be a parabolic function. Then, two of three model parameters can be retrieved; to obtain the third parameter one has to make an assumption about the value of prefactor for conductivity. Applying the proposed analysis scheme to Ge2Sb2Te5, reasonable values of Fermi level position are obtained and the change of Fermi level as a result of resistance drift phenomenon is demonstrated.

Innovative Nanocomposites for Low Power Phase‐Change Memory: GeTe/C Multilayers

“…The resistance drift is ascribed to a structural relaxation of the amorphous phase with aging but its precise origin in amorphous chalcogenide phase‐change materials is still debated. [ 19–21 ] The drift phenomenon is usually described by an empirical power law , where R ( t ) is the resistance at time t , R 0 is the resistance at time t 0 , and ν the drift exponent. [ 22 ] To investigate the drift of [(GeTe) 4 nm /C 1 nm ] 10 devices annealed at 425 °C, the R ( t ) curves of 6 ML devices were measured after the RESET operation.…”

Fabrication of stable multi-level resistance states in a Nb-doped Ge2Sb2Te5 device

“…The applied electric field, composition deviation, phase separation, and randomly distributed defect states could lead to spontaneous structural relaxation in phase-change-based devices. 12 Structural relaxation is usually manifested as resistance drift, which is a big obstacle for neuro-inspired computing. 13 The drift effect must be controlled and reduced.…”

The improvement of endurance characteristics in a superlattice-like material-based phase change device

“…In addition, both the properties of the phase-change material and the quality of the electrode determine the device endurance characteristics. The repeated SET-RESET operation always leads to material failure problems, such as composition deviation and phase separation [10]. Consequently, a serious challenge regarding the reliability of the phase-change material and electrode contact occurs.…”