Atomic disordering processes in crystalline GeTe induced by ion irradiation

Abstract

The damaging process of GeTe up to amorphization has been studied by introducing controlled levels of disorder by irradiation with 150 keV Ar + ions. In situ reflectivity measurements and exsitu resistance and Raman spectroscopy analysis have been employed to study the impact of ion bombardment on the electrical conduction properties and on the bonding. The results obtained are indicative for three different stages of film damage. The first step appears to be dominated by point defects, affecting the temperature coefficient of resistance (TCR) and inducing a transition from positive (metallic conduction) to negative TCR values (conduction dominated by localized states), whilst the material still remains crystalline. The second step is characterized by the annealing of the defects induced, presumably, by the formation of complex defects that act as sinks for point defect recombination. This process is facilitated by the high atomic mobility. The third phase of damage starts at a fluence of 3.5 × 10 14 cm −2 and finally converts the material to the amorphous state, characterized by higher resistance and decreased optical reflectivity. The modifications observed upon ion irradiation provide important insights into the possible states that can be achieved in crystalline GeTe through different local atomic arrangements towards amorphization.

Disordering process of GeSb2Te4 induced by ion irradiation

“…When the irradiation is performed at room temperature, the fluence required to decrease the reflectivity to a minimum value is higher, since dynamic annealing may induce partial disorder recovery, as already observed in previous studies [26][27][28]. However, large differences are observed by comparing the trigonal film epitaxially grown on Si(1 1 1) (Tri/ Si(1 1 1)) to the polycrystalline one, (Tri/SiO 2 ) on SiO 2 .…”

“…For low temperature irradiation (77 K) the minimum of the reflectivity corresponds to complete amorphization of the material, as checked by XRD, Raman spectroscopy, and electrical measurements [26][27][28]. The value at which the reflectivity reaches 1/e of its maximum can be defined as the amorphization threshold.…”

Recent advances in doped Ge2Sb2Te5 thin film based phase change memories

“…157 These ions can modify the activation energy and the resistivity of these thin films by controlling the fluence rate of irradiation. Irradiation with 150 keV Ar + ions can be used to modify the structural and electrical properties of the GST thin films as shown by Privitera et al 158,159 These ions lead to the interesting metal-insulator transitions in these materials by tuning the bonding and the van der Waals gap.…”