Characterization of Sputter Deposited PbTe on Si (111) for Optoelectronic Applications
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Characterization of Sputter Deposited PbTe on Si (111) for Optoelectronic Applications Alexey Jdanov, Zinovi Dashevsky, Joshua Pelleg and Roni Shneck Department of Materials Engineering, Ben Gurion University of the Negev Beer Sheva, 84105, Israel ABSTRACT IV-VI compound semiconductors are of interest due to their potential application as thermoelectric material, infrared detectors and semiconductor lasers. The use of PbTe based semiconductors is usually in the middle and far infrared region. Magnetron sputtering of PbTe thin films from a single target on Si (111) was performed under various conditions. Characterization of the films shows that PbTe films on Si (111) substrate are suitable for preparation of infrared (IR) detectors. By heat treatment novel IR detectors can be developed in the electron absorption region of 4 – 10 µm. INTRODUCTION It was reported in earlier communications [1,2] that film thickness dependent single crystal-like PbTe can be obtained on Si (111) despite the large mismatch of ~ 19% between the Si substrate and the PbTe film. Si substrates offer significant advantages over other because of price, size and its mechanical properties. In this communication, we report the results of band gap, Eg, evaluation of polycrystalline PbTe films on Si (111) substrates. It was found that Eg is larger than that of bulk or single crystal specimens and its value is thickness dependent. At a film thickness larger than 2 µm, Eg approaches the bulk value of PbTe. The magnetron deposited films were characterized by X-ray diffraction (XRD), secondary electron microscopy (Auger), and their structure was observed by highresolution electron microscopy (HRTEM). EXPERIMENTAL DETAILS In order to simplify PbTe fabrication process, films were grown on Si (111) substrates by RF magnetron sputtering without the use of buffer layers. A single compound target of PbTe was used. Good adhesion of the PbTe layers on Si (111) was obtained despite the large mismatch between Si substrate and PbTe film and despite of the 0.2-0.3 GPa stress induced by the difference in the thermal expansion coefficients between them. Before loading into the chamber, substrates were cleaned using a solution of HF:HFO3:CH3COOH (3:5:3). The base pressure before introducing Ar into the sputter chamber was ~6.7x10-5 Pa. The PbTe target was presputtered in Ar at a pressure of ~0.6 Pa for about 30 min and it was followed by sputtering at the same Ar pressure. The deposition was done to a PbTe thickness of 100-2000 nm at a constant power supply of 40 W for different sputter times. Specimens were heat treated at ~520 K in the sputtering chamber during the deposition. XRD data were obtained by the use of a Rigaku
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diffractometer. The composition and structural details were obtained by Auger spectroscopy and HRTEM, respectively. Spectroscopy was used to evaluate transmission. Computer controlled optical spectrometer consisting of a light source, a monochromator and a pyroelectric radiometer were used for the measurements. RESULTS AND DISCUSS
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