Thin films of amorphous Ga2S3 and rare-earth sulphides
Introduction
Chalcogenide glasses based on Ga2S3 have interesting applications in optics and optoelectronics [1] such as infrared and mid-infrared lasers [2], fiber optics amplifiers [3]. They can be drawn into optical fibers [4], can form waveguides [5] or can be doped by high concentrations of RE-ions [6]. Sulphide glasses are wide band gap semiconductors (1.5–3.6 eV) making them promising candidates for optoelectronics and photovoltaics.
The best known RE gallium-sulphides glasses are the gallium–lanthanum-sulphide glasses which have been proposed as RE hosts for 1.3 μm optical amplification devices [7]. Recently Pompilian et al. [8] have prepared and investigated amorphous thin films of Er- and Pr-doped Ga–La-S.
Using the same techniques (SPS and PLD), Yang et al. [9] have obtained high-quality crystalline thin films of the ferromagnetic insulator europium (II) sulphide (EuS).
We report in this paper the preparation and properties of amorphous thin films based on undoped gallium sulphides and doped by rare-earth sulphides, and on rare-earth sulphides.
Section snippets
Materials and methods
Ga2S3 (purity 99.99%) and rare-earth sulphides powders (Alpha-AESAR and CHEMOS GmbH) were used to prepare mixtures under ambient conditions by manually grinding for 360 s in an agate mortar. These mixtures with compositions of (Ga2S3)0.95(RexSy)0.05 at%, (where RexSy=EuS, Er2S3 and Gd2S3) were used to prepare disc-shaped bulk samples by SPS. Using the same technique, additional disc-shaped bulk samples of EuS, Er2S3 and Gd2S3 have been prepared.
For Spark Plasma Sintering we have used a
Results and discussion
X-ray diffraction: The X-ray diffraction diagrams of the thin films are shown in Fig. 1b–h. All the PLD prepared films are amorphous. One observes in Fig. 1b, c, e, g (Ga2S3, Ga2S3:EuS, Ga2S3:Er2S3, Ga2S3:Gd2S3) a well-developed first sharp diffraction peak (FSDP), as can be seen in the case of As2S3 amorphous thin film (Fig. 1a). This speaks in favour of the quasi-bidimensional layers with disordered configuration, similar to the structure found in As2S3 glass and thin films.
Ellipsometry: The
Conclusions
The Spark Plasma Sintering proved to be the most suitable method for obtaining the disk shaped PLD-targets. Thin amorphous films based on Ga2S3 and RE-sulphides were obtained by Pulsed Laser Deposition on glass and silicon substrates. XRD diagram of amorphous Ga2S3 thin film speaks in favour of a structure with disordered layers, similar to the structure of the amorphous As2S3 thin films. The refractive index of amorphous Ga2S3 thin film is 2.95 at 400 nm wavelength. A photoexpansion effect in
Acknowledgement
The authors thank S. Miclos and D. Savastru for the calculation of the photoexpansion value and A. Balan for the AFM measurements. They kindly acknowledge the financial support of the Ministry of National Education (Romania) in the frame of the Project NANOVISMAT PN2-162/2012.
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