Dielectric properties of vacuum deposited Bi2Te3 thin films

Multi-component alloys based on tellurium are used as switching materials, which induce the interest in studying these materials in the bulk and thin film states. Bi2Te3 films of various thicknesses were prepared and its structural, composition and surface morphological analysis were carried out. Thickness of the films was measured by an in built Quartz Crystal Monitor. From the X-ray diffraction patterns it is observed that the films possess polycrystalline rhombohedral structure. Using Scherer's formula the grain size (D) was calculated and it is found that the D value increases with increase of film thickness. The budding of micro crystallites were observed by the SEM analysis of Bi2Te3 thin film. The composition of the film is analyzed by EDAX and found that Bi:Te=3:2. Thin film capacitors Al-Bi2Te3-Al were formed onto well-cleaned glass substrates by vacuum deposition method under a pressure of 10−5 Torr. The values of capacitance (C) and tan δ were measured using a digital LCR meter at various frequencies (12 Hz-100 K Hz) and temperature (303-483 K). Knowing the value of C, d and area of the capacitor (A), the dielectric constant (ε′) was calculated. The loss peak observed in tan δ vs. frequency plot reveals the presence of relaxation effect. For a Debye process at higher temperatures and for given frequency, a maximum in tan δ will occur at a temperature such that 2πfrelax=1/τ. Cole-Cole plots over the audio frequency for two different temperatures are plotted and the relaxation time τ has been estimated and is found to be temperature dependent. The TCC and TCP values have been evaluated as 8.18×10−3 and 6.78×10−3 ppm/K, respectively for 100 KHz at 400 K. The high value of TCC suggests that these capacitors may be used as temperature sensors also.