The influence of a temperature dependent bandgap on the energy scale of modulated photocurrent experiments

Luckas, Jennifer; Kremers, Stephan; Krebs, Daniel; Salinga, Martin; Wuttig, Matthias; Longeaud, Christophe

doi:10.1063/1.3605517

Cited by 34 publications

(29 citation statements)

References 32 publications

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“…An ohmic regime of conductivity can be observed for all materials down to the lowest temperatures (see supplementary material 17 ). Furthermore, the measured activation energy for our GeTe and GST devices with tungsten electrodes is $0.37 eV and is in line with values measured on GeTe and GST on aluminum 35 or gold electrodes, 19 i.e., $0.4 eV at room temperature. This value corresponds well to half the optical band gap in all materials studied.…”

Section: Discussionsupporting

confidence: 64%

“…Various studies of the density of states of GeTe have indicated the presence of both a valence-band tail and deep defects. 30,35 Apart from the energetic positions and magnitudes of these defects, the external circumstances under which a specific defect can dominate field assisted emission depend on additional parameters. These parameters are for instance the potential to be chosen in the evaluation of field assisted emission (at low fields) and the effective mass m*, which strongly influences tunneling (at high fields).…”

Section: Behavior At High Fields-full Tunneling Modelmentioning

confidence: 99%

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High-field electrical transport in amorphous phase-change materials

Kaes

Gallo

Sebastian

et al. 2015

Journal of Applied Physics

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Electrical transport in chalcogenide-based phase change materials is an active area of research owing to the prominent role played by these materials in the field of information technology. Here, we present transport measurements (IV curves) obtained on line-cells of as-deposited amorphous phase change materials (Ge2Sb2Te5, GeTe, Ag4In3Sb66Te27) over a wide voltage and temperature range (300 K to 160 K). The well defined geometry of our devices enables a description of the transport behavior in terms of conductivity vs. electric field. At higher temperatures (300 K ≥ T ≥ 220 K) and low to intermediate fields (F < 20 V/μm), the data can be described within the framework of a previously developed model, which is based on multiple trapping transport together with 3D Poole-Frenkel emission from a two-center Coulomb potential. Based on this model, we observe a temperature dependence of the inter-trap distance, which we can relate to a temperature dependence in the occupation of the defect creating the Coulomb potential governing Poole-Frenkel emission. At higher fields and lower temperatures, the dependency of the IV curve on the electric field can be described by ln(I/I0) = (F/Fc)2. By combining this contribution with that of the Poole-Frenkel emission, we can show that the slope at high fields, Fc, is independent of temperature. We argue that models based on direct tunneling or thermally assisted tunneling from a single defect into the valence band cannot explain the observed behavior quantitatively.

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Section: Discussionsupporting

confidence: 64%

Section: Behavior At High Fields-full Tunneling Modelmentioning

confidence: 99%

High-field electrical transport in amorphous phase-change materials

Kaes

Gallo

Sebastian

et al. 2015

Journal of Applied Physics

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“…This result agrees that ESR signals are not observed in dark conditions even existing defect states in amorphous chalcogenides. Sub-gap states in amorphous Ge 2 Sb 2 Te 5 were investigated using modulated photocurrent measurement (MPC) [11]. MPC spectra show that the position of the deep defect is at midgap.…”

Section: Discussionmentioning

confidence: 99%

Sub-gap states in Ge2Sb2Te5 phase change films

Gotoh

2012

Journal of Non-Crystalline Solids

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“…A detailed description of this procedure is presented in Ref. 18. data, corrected for the band gap variations, we have obtained for one of the a-GeTe films studied.…”

Section: Resultsmentioning

confidence: 99%

On the density of states of germanium telluride

Longeaud

Luckas

Krebs

et al. 2012

Journal of Applied Physics

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Germanium telluride (GeTe) is one of the most studied phase change materials. Surprisingly, only little is known about the density of states (DOS) in its band gap. In this paper, the DOS of amorphous GeTe films is investigated both experimentally and theoretically. We propose a model for this DOS as well as estimates of some of the transport parameters of this material. Thin films of amorphous GeTe have been deposited by sputtering. Their dark and photoconductivity have been measured as a function of temperature. By means of the modulated photocurrent technique their DOS was probed, while their absorption was investigated by photothermal deflection spectroscopy at room temperature. Numerical calculations were employed to reproduce the experimental results with a proper set of transport parameters and choice of DOS. These data constitute a good basis for further study on the influence of the DOS on the aging of the sample resistance (“resistance drift”).

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The influence of a temperature dependent bandgap on the energy scale of modulated photocurrent experiments

Cited by 34 publications

References 32 publications

High-field electrical transport in amorphous phase-change materials

High-field electrical transport in amorphous phase-change materials

Sub-gap states in Ge2Sb2Te5 phase change films

On the density of states of germanium telluride

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