Structural and electrical properties of Ge1Sb2Te4 face centered cubic phase

Abstract

The aim of this article is to study the properties of the crystalline face centered cubic Ge 1 Sb 2 Te 4 phase as a function of annealing and measuring temperature. This material is one of the stoichiometric members of the Ge:Sb:Te family, which is widely used in the phase change data storage and one candidate for multistate recording. The electrical properties of this material have been investigated using two independent methods, the four probe impedance and the Hall measurements, and the results are interpreted in terms of structural parameters obtained from x-ray diffraction and transmission electron microscopy results. Experimental results have shown the polycrystalline nature of the film and that the transport properties have a strong dependence on the annealing temperature. An increase in the annealing temperature leads to an increase in the grain size, carrier concentration, mobility, and to a decrease in the volume fraction of grain boundaries. The mobility is limited by scattering of charge carries at the grain boundaries and can be described by a conduction model based on thermionic emission over the potential barriers. The large changes in the room temperature resistivity ͑more than 25 times͒ and effective capacitance ͑about 30%͒ of the polycrystalline state upon annealing due to various structural configurations increase ͑in addition to the amorphous in the crystalline transition͒ the dynamical range for multistate recording applications.

Disorder‐Induced Localization in Crystalline Pseudo‐Binary GeTe–Sb2Te3 Alloys between Ge3Sb2Te6 and GeTe

“…As Zhang et al, [ 4 ] Prokhorov et al, [ 5 ] Siegrist et al, [ 6 ] and Volker et al [ 8 ] have already done the former and elucidated the impact of annealing temperature on step-annealed fi lms of Ge 1 Sb 2 Te 4 , elaborating the stoichiometry aspect seems most rewarding. For this reason, the data that will be discussed in the following were obtained from initially as-deposited amorphous fi lms, which were annealed (and crystallized) at 275 °C (GeTe) and 250 °C (all other compositions) prior to the measurements, i.e., we varied the stoichiometry x , but kept the annealing temperature constant (275/250 °C).…”

“…Following the experimental procedures already applied and outlined in a previous study, [ 6 ] we characterized the electrical, optical, and structural properties of the fi lms by sheet resistance, Hall effect, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). However, in contrast to preceding investigations, [4][5][6][7] where the annealing temperature T a was varied at constant stoichiometry x (Siegrist et al: [ 6 ] T a = 150 ... 325 °C, x = 1/2), we varied the stoichiometry rather than the annealing temperature ( T a = 250/275 °C, x = 3/4 ... 1).…”

“…[ 6 ] Hall effect and thermopower measurements agree that crystalline GeSbTe fi lms are p type. [4][5][6][7]16,26,27 ] Moreover, there is little doubt that Ge 1 Sb 2 Te 4 fi lms which have been annealed at temperatures above 250 °C can be regarded as ordinary degenerate semiconductors, where the Fermi level intersects the valence band and the wave functions in the vicinity of the Fermi level are extended Bloch waves. [ 6 ] Bahl and Chopra [ 28 ] pointed out that the electrical properties of crystalline (rhombohedral) GeTe can be readily understood by a simple model consisting of a parabolic and isotropic valence band maximum.…”

RESET failure analysis of phase change memory based on Ge₂Sb₂Te₅

“…3(c). It has been confirmed that the carrier concentration of GST-124 is much higher than that of GST-225 in both amorphous and polycrystalline state, and the mobility and the thermal conductivity of the two materials are not very different [13,14]. The conductivity of the materials can be given by the equation (1) as follows:…”

Coexistence of electron-glass phase and persistent photoconductivity in GeSbTe compounds

“…18 cm -3 [32] to ≈10 22 cm -3 [29]. Also, the large dielectric constant of GeSb x Te y [28] further reduces the energy-cost associated with carrier-concentrations gradients.…”