Defect models and electrical storage mechanism in GeSbTe phase change materials

Huang, Bolong; Robertson, John

doi:10.1016/j.jnoncrysol.2011.11.017

Cited by 18 publications

(13 citation statements)

References 45 publications

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“…4(e)). In amorphous GeTe, E F is already pinned at the mid-gap by many mechanisms, as reported in previous works [22,28]. Thus, the small number of N-doping-induced gap states does not alter the E F behavior at the mid-gap in the amorphous phases.…”

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confidence: 76%

Nature of electrical resistivity and structural stability in N-doped GeTe models for reliable phase-change materials

Huang

2014

Phys. Status Solidi B

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We study the effects of nitrogen (N)‐doping on the electrical memory reliability of GeSbTe phase‐change materials based on GeTe prototype models. We find that the loss of secondary bonding (e.g., resonant interlayer bonding) determines the feasibility of various types of N‐doping that can be easily adopted by the GeSbTe system. We give a more generalized explanation beyond compliance with the formation of local Ge3N4 motifs. The nitrogen‐induced change in local order produces crystalline GeTe with shallow states near the valence band edge. These states are localized on the nearest‐neighbor Ge sites, thus reducing the conductivity in the crystalline phase. This trend carries over to c‐GeTe with Ge vacancy. The N‐doped amorphous GeTe models exhibit enhanced degrees of band tail overlap, which pins the Fermi energy in the mid‐gap and thus gives rise to even higher resistivities in the amorphous phases.

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confidence: 76%

Nature of electrical resistivity and structural stability in N-doped GeTe models for reliable phase-change materials

Huang

2014

Phys. Status Solidi B

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“…A similar concept has been successfully utilized in other solid functional materials in our theoretical modeling. 34,[41][42][43] The key difference between UMPL materials and conventional PL materials is that the electrons and holes can be separated and allocated at the deep localized levels in the optical band gap area, due to the extra deep trap levels near the valence band maximum (VBM) and the extra hole traps near the conduction band maximum (CBM), as shown in Fig. 1.…”

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confidence: 99%

Energy harvesting and conversion mechanisms for intrinsic upconverted mechano-persistent luminescence in CaZnOS

Huang

2016

Phys. Chem. Chem. Phys.

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We interpreted the mechanisms of energy harvesting and conversion for intrinsic upconverted mechano-persistent luminescence in CaZnOS through a native point defects study. We found that vacancy defects such as Zn and O vacancies, as well as Schottky pair defects, act as energy harvesting centers; they are very readily formed and very active. They are found to be extra deep electron or hole trap levels near the valence or conduction band edges, respectively. This leads to a coupling and exchange effect to continuously collect and transport host charges along a path via localized states to deep recombination levels. The initiating energy barrier is small and can be overcome by ambient thermal stimulation or quantum tunneling. Native activators such as V

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“…Impedance spectroscopy and I-V measurements show a similar temperature dependence for resistance and relaxation frequency with activation energies of about 0.36 eV, which identifies the location of the Fermi level in the forbidden energy gap [11]. When this value is compared with the measured optical gap [12,13], it showed that the Fermi level is pinned in the middle of the band gap and confirms the chalcogenide nature of Ge 2 Sb 2 Te 5 films [14]. Additionally, modulated photocurrent measurements performed on amorphous Ge 2 Sb 2 Te 5 display a pronounced valence band tail and two defect states [15].…”

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confidence: 65%

Defect states in amorphous Ge₂Sb₂Te₅ phase change material

2014

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Steady-state photoconductivity measurements in the temperature range 100-300 K on amorphous Ge 2 Sb 2 Te 5 thin film prepared by dc sputtering are analyzed. The dark conductivity is thermally activated with a single activation energy that allocates the position of the Fermi level approximately in the middle of the energy gap relative to the valance band edge. The temperature dependence of the photoconductivity ensures the presence of a maximum normally observed in chalcogenides with low-and high-temperature slopes, which predict the location of discrete sets of localized states (recombination levels) in the gap. The presence of these defect states close to the valence and conduction band edges leaves the quasi Fermi level shifts in a continuous distribution of gap states at high temperatures, as evidenced from the ␥ values of the lux-ampere characteristics.Résumé : Nous analysons les mesures de photoconductivité stationnaire entre 100 et 300 K sur des films minces de Ge 2 Sb 2 Te 5 préparés par pulvérisation. La conductivité en obscurité est activée thermiquement par une simple énergie d'activation qui positionne le niveau de Fermi au milieu de la bande interdite (gap) relative au voisinage de la bande de valence. La dépendance en température de la photoconductivité garantit la présence d'un maximum normalement observé dans les chalcogénures avec des pentes à basse et à haute température qui prédisent la localisation d'ensembles discrets d'états localisés (niveau de recombinaison) dans la bande interdite. La présence de ces états défauts près des limites des bandes de valence et de conduction laisse le quasi-niveau de Fermi se déplacer dans une distribution continue d'états du gap à haute température, tel que mis en évidence par les valeurs de la caractéristique ␥ de lux-ampere. [Traduit par la Rédaction]

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Defect models and electrical storage mechanism in GeSbTe phase change materials

Cited by 18 publications

References 45 publications

Nature of electrical resistivity and structural stability in N-doped GeTe models for reliable phase-change materials

Nature of electrical resistivity and structural stability in N-doped GeTe models for reliable phase-change materials

Energy harvesting and conversion mechanisms for intrinsic upconverted mechano-persistent luminescence in CaZnOS

Defect states in amorphous Ge₂Sb₂Te₅ phase change material

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Defect models and electrical storage mechanism in GeSbTe phase change materials

Cited by 18 publications

References 45 publications

Nature of electrical resistivity and structural stability in N-doped GeTe models for reliable phase-change materials

Nature of electrical resistivity and structural stability in N-doped GeTe models for reliable phase-change materials

Energy harvesting and conversion mechanisms for intrinsic upconverted mechano-persistent luminescence in CaZnOS

Defect states in amorphous Ge2Sb2Te5 phase change material

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Defect states in amorphous Ge₂Sb₂Te₅ phase change material