J. Gutwirth

Ag–Sb–S amorphous chalcogenide thin films prepared by optically induced dissolution and diffusion of silver

Abstract The kinetics of optically induced dissolution and diffusion of silver in Sb33S67 films were measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled reflectivity technique. Silver concentration was traced by the means of energy dispersion X-ray microanalyzer. The composition of the Sb–S films was chosen to be Sb33S67, which is the most favorable for optically induced solid-state reaction, because it yields homogeneous photodoped products. A new technique of step-by-step optically induced solid state reaction of Ag into Sb33S67 amorphous films, which has allowed the design of films with exact silver concentration and the study of their properties, is reported. The host Sb33S67 films were photodoped by dissolving a thin (∼60 nm) layer of silver, which resulted in homogeneous films of good optical quality. The silver concentration of the films ranged between 1 and 11 at.%. We have analyzed in detail the influence of the silver doping and its structure in the host material on optical properties. Analysis of the measurements have helped to understand the processes taking place during silver photodissolution.

Crystallization kinetics of a-Se, part 4: thin films

Differential scanning calorimetry was used to study the crystallization behaviour of selenium thin films in dependence on film thickness and deposition rate. In the current work, which is the fourth in a sequence of articles dealing with crystallization kinetics of a-Se, the non-isothermal crystallization kinetics was described in terms of the Johnson-Mehl-Avrami nucleation-growth model. Two-dimensional crystallite growth, consistent with the idea of sterically restricted crystallization in a thin layer, was confirmed for all data. It was found that neither the film thickness (tested within the 100–2350 nm range) nor the deposition rate appears to have any significant influence on the crystallization kinetics. However, the higher amount of intrinsic defects possibly produced by a higher deposition rate seems to accelerate the crystallization, shifting it towards lower temperatures. Very good correlation between the results obtained for thin films and those for fine powders was found. Based on the obtained results, interpretations of relevant literature data were made.

Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films.

Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers.

Ag-Sb-S Thin Films Prepared by RF Magnetron Sputtering and Their Properties

One of the recent applications of thin chalcogenide films is rewritable optical data recording. This technology is based on reversible phase transition between crystalline and amorphous state and vice versa. Dominant materials for rewritable optical recording are Ge Sb Te and Ag In Sb Te alloys. Material research still continues due to need of increasing storage capacity and data rates. Thin Ag Sb S films were prepared by RF magnetron sputtering as potential candidates for rewritable optical data storage films. There were prepared polycrystalline bulks of AgSbS 2 . Composition and homogeneity of these bulks were checked by scanning electron microscopy with energy dispersive analysis (SEM EDX) structure and bonding relations were studied by Raman spectroscopy and × ray diffraction (XRD). Targets for RF magnetron sputtering were prepared from pulverized bulks by hot pressing technique. Targets were characterized the same way as bulks. Composition and homogeneity of prepared thin films were characterized by SEM EDX, character (amorphous/crystalline) was studied by XRD. Optical properties (spectral dependence of refractive index) were evaluated on basis of UV Vis NIR spectroscopy and variable angle spectral ellipsometry (VASE). Crystallization abilities were traced by thermal dependence of optical transmission of prepared thin films.

Amorphous Ge-Sb-Se thin films fabricated by co-sputtering Properties and photosensitivity

Amorphous Ge-Sb-Se thin films were fabricated by a rf-magnetron co-sputtering technique employing the following cathodes GeSe2, Sb2Se3, and Ge28Sb12Se60. The influence of the composition, determined by energy-dispersive X-ray spectroscopy, on the optical properties was studied. Optical properties were analyzed based on variable angle spectroscopic ellipsometry and UV-Vis-NIR spectrophotometry. The results show that the optical bandgap range 1.35-2.08 eV with corresponding refractive index ranging from 3.33 to 2.36 can be reliably covered. Furthermore, morphological and topographical properties of selenide-sputtered films studied by scanning electron microscopy and atomic force microscopy showed a good quality of fabricated films. In addition, structure of the films was controlled using Raman scattering spectroscopy. Finally, irreversible photoinduced changes by means of change in optical bandgap energy and refractive index of co-sputtered films were studied revealing the photobleaching effect in Ge-rich films when irradiated by near-bandgap light under Ar atmosphere. The photobleaching effect tends to decrease with increasing antimony content.

Co-sputtered amorphous Ge-Sb-Se thin films: optical properties and structure

The unique properties of amorphous chalcogenides such as wide transparency in the infrared region, low phonon energy, photosensitivity and high linear and nonlinear refractive index, make them prospective materials for photonics devices. The important question is whether the chalcogenides are stable enough or how the photosensitivity could be exacerbated for demanded applications. Of this view, the Ge-Sb-Se system is undoubtedly an interesting glassy system given the antinomic behavior of germanium and antimony with respect to photosensitivity. The amorphous Ge-Sb-Se thin films were fabricated by a rf-magnetron co-sputtering technique employing the following cathodes: GeSe2, Sb2Se3 and Ge28Sb12Se60. Radio-frequency sputtering is widely used for film fabrication due to its relative simplicity, easy control, and often stoichiometric material transfer from target to substrate. The advantage of this technique is the ability to explore a wide range of chalcogenide film composition by means of adjusting the contribution of each target. This makes the technique considerably effective for the exploration of properties mentioned above. In the present work, the influence of the composition determined by energy-dispersive X-ray spectroscopy on the optical properties was studied. Optical bandgap energy Egopt was determined using variable angle spectroscopic ellipsometry. The morphology and topography of the selenide sputtered films was studied by scanning electron microscopy and atomic force microscopy. The films structure was determined using Raman scattering spectroscopy.

Characterization of RF magnetron sputtered Se-doped Ge2Sb2.3Te5 thin films

RF magnetron sputtering technique has been used to deposit new films potentially applicable in phase-change memories. Ge2Sb2Te5 seems to be promising material, but it is not clear whether it is optimum composition for such application. We studied different deposition conditions and deposition of films doped by excess of Sb and doped also by Se, which equally replaces Te atoms compare to Ge2Sb2Te5. The sputtering target composition for our study was Ge2Sb2.3Te4Se1. Sputtered films contained less Se than target. Deposited films were characterized as-deposited and after thermal treatment in temperature range 30 – 300 °C.