Abstract
Ge-Sb-Te thin films were obtained by ns-, ps-, and fs-pulsed laser deposition (PLD) in various experimental conditions. The thickness of the samples was influenced by the Nd-YAG laser wavelength, fluence, target-to-substrate distance, and deposition time. The topography and chemical analysis results showed that the films deposited by ns-PLD revealed droplets on the surface together with a decreased Te concentration and Sb over-stoichiometry. Thin films with improved surface roughness and chemical compositions close to nominal values were deposited by ps- and fs-PLD. The X-ray diffraction and Raman spectroscopy results showed that the samples obtained with ns pulses were partially crystallized while the lower fluences used in ps- and fs-PLD led to amorphous depositions. The optical parameters of the ns-PLD samples were correlated to their structural properties.
Highlights
Important advances in nonvolatile solid state memory devices were driven by the discovery of Ge-Sb-Te (GST) alloys along the GeTe-Sb2Te3 tie-line in the mid-1980s [1]
Analyzing the thin films deposited by nanosecond laser ablation, we observed that the sample thickness was influenced by the laser wavelength, fluence, target-to-substrate distance, and deposition time
Ellipsometric measurements done on the Ge-Sb-Te thin films revealed n and k values between the ones of amorphous and crystalline samples reported in Reference [31], confirming the structural analysis results
Summary
Important advances in nonvolatile solid state memory devices were driven by the discovery of Ge-Sb-Te (GST) alloys along the GeTe-Sb2Te3 tie-line in the mid-1980s [1]. Phase change (PC) memories are based on changes in optical properties and electrical conductivity of chalcogenide materials upon a rapid amorphous-to-crystalline phase transition and vice versa. These two states must present a high enough contrast in electrical resistivity or other (optical) parameters in order to be identified. The rapid laser-induced crystallization with large property changes represented the grounds for many research studies [3,4,5,6,7,8,9]. The degree of the optical change n,k (crystalline)-n,k (amorphous) on the GeTe-Sb2Te3 pseudo-binary line increases with an increasing Ge content [10], but GST chalcogenides with higher Sb concentrations present faster phase changes. The study of Ge-Sb-Te-based compounds in various compositions is essential when developing phase change devices with remarkable characteristics [11]
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