H. D. Banerjee

Some optical properties of evaporated zinc telluride films

The absorption and transmission of ZnTe thin films are measured at wavelengths of 0.32-2.3 mu m. The optical constants (n, K) are measured in this range, although the short wavelength refractive index n measurement is limited by the band gap. A theoretical calculation of n near the band gap is made from experimental parameters. An explanation is given for the abnormal decrease of refractive index near the band gap. The effects of film thickness and doping with impurities like In, PbCl2, BaF2 have also been investigated. Effective crystallite size and strain have been determined by the method of variance analysis of the X-ray diffraction line profile on the same films. Lattice constants have also been calculated using the Nelson-Riley plots. It has been observed that there is an increase in optical band gap with decrease in crystallite size, increase in strain and decrease in lattice constant value.

Production and purification of silicon by calcium reduction of rice-husk white ash

Polycrystalline silicon of reasonable purity has been prepared by metallothermic reduction of purified rice-husk white ash (amorphous silica) by using calcium. The mechanism of reduction of the silica with calcium was investigated using simultaneous thermogravimetric analysis and differential thermal analysis, which revealed the reduction temperature to be around 720‡ C. The paper also discusses the method of preparation of silicon and its purification procedure. Characterization of the silicon sample thus prepared was made by X-ray diffraction, scanning electron microscopy and emission spectrography.

Electrocal, thermal, thermoelectric and related properties of magnesium silicide semiconductor prepared from rice husk

Polycrystalline, 10μm size magnesium silicide was prepared by alloying 99.9% purity polycrystalline silicon obtained from rice husk ash and high-purity magnesium powder. The material in sintered pellet form was characterized for its structural, electrical, thermal, thermoelectric and other properties. A typical sintered pellet exhibited a room-temperature (30°C) thermoelectric power of 565 μV K−1 and an electrical resistivity of 35 Ω cm. On the other hand, the material was found to be thermally quite stable up to 650°C with a room-temperature thermal conductivity of 6.3×10−3cals−1cm−1K−1 (2.6 J s−1 m−1 K−1). These properties of the material indicate that the material can find potential applications as a thermoelectric generator and in other semiconductor devices. Furthermore, an indigenous technology for large-scale production of silanes (SiH4) can be developed using this Mg2Si which could be prepared in large quantities by a simple and low-cost process.

Structural and optical properties of CdSexTe1 − x thin films grown by electron beam evaporation

Abstract CdSe x Te x − 1 (0≤ x ≤1) ternary thin films have been deposited on glass substrates at room temperature by electron beam evaporation, using the source materials prepared in our laboratory by direct reaction of high purity elemental Cd(99.9999%), Se(99.999%) and Te(99.999%). These alloy films independent of composition, are polycrystalline, single phase (zinc blende structure) with strong preferential orientation of the crystallites (30–50 nm size) along (111) direction. Linear variation of lattice constant with composition ( x ) is observed. Absorption measurements show quadratic variation of bandgap with composition ( x ). Refractive indices, determined from transmission spectra, are in the range 2.43–2.52 depending upon the composition of the films.

Studies on physical and thermal properties of rice husk related to its industrial application

The physical and thermal properties namely, bulk density, true density, angle of repose, specific heat and thermal conductivity of both unground and ground rice husk at different moisture contents ranging from 10 to 20%, wet basis (wb) have been found. Except for the angle of repose, the values of the other properties were higher for the ground husk than those of the unground ones. Various possible industrial applications of both unground and ground husk (e.g. production of insulation board, packing material and ceramics) have been discussed.

Electrical properties of stacked gate dielectric (SiO2/ZrO2) deposited on strained SiGe layers

Abstract Stacked silicon and zirconium dioxide (SiO 2 /ZrO 2 ) films have been deposited on strained-Si 0.91 Ge 0.09 layer at a low temperature using zirconium tetratert butoxide (ZTB) and ZTB/O 2 in a microwave plasma deposition system. Electrical properties of the as-deposited and annealed (in N 2 at 500 °C) samples have been measured from the high frequency capacitance–voltage, conductance–voltage and current–voltage characteristics of metal insulator semiconductor capacitor structures fabricated using the stacked dielectrics. The superiority of stacked (SiO 2 /ZrO 2 ) gate dielectric is shown.

Metallo-organic compound-based plasma enhanced CVD of ZrO2 films for microelectronic applications

ZrO2films on silicon wafer were deposited by microwave plasma enhanced chemical vapour deposition technique using zirconium tetratert butoxide (ZTB). The structure and composition of the deposited layers were studied by fourier transform infrared spectroscopy (FTIR). The deposition rates were also studied. MOS capacitors fabricated using deposited oxides were used to characterize the electrical properties of ZrO2films. The films showed their suitability for microelectronic applications.

Energy storage behaviour of some binary alkali borate glasses by thermoluminescence studies

Thermoluminescence behaviour of a series of binary alkali borate glasses has been investigated to study their energy storage mechanism. Sodium borate glasses of varying composition have been prepared and their glow curves recorded after exposing them to X-rays (CuKα radiation, 30 kV, 10 mA) of different dosages at room temperature. The effect of the nature and concentration of alkali oxide and the dose of irradiation on the nature of thermoluminescent glow curves were also studied. Borate glasses containing different concentrations of Na2O exhibit significantly different glow curves. These glow curves have been analysed and the nature of traps responsible for TL emission are tentatively identified. The broad and complex nature of the glow pattern is attributed to distribution of trap depths in these materials. The viability of borate glasses in the construction of TL dosimeters are discussed.

Temperature dependence of electrical properties of N2O/O2/N2O-grown oxides on strained SiGe

Temperature dependence of electrical properties of split-N2O grown oxides on strained SiGe layers by rapid thermal oxidation is reported. The reliability and thermal stability of ultrathin oxides have been examined by high frequency capacitance–voltage and current density versus electric field measurements. It is observed that at a low ( 11 MV/cm) electric field, however, the leakage current is mainly governed by the Fowler–Nordheim tunneling. Charge-to-breakdown measurements at a constant current stressing show a higher reliability for the split-N2O grown oxides.

The anomalous photovoltaic effect in polycrystalline zinc telluride films

The anomalous photovoltaic effect has been studied in polycrystalline ZnTe films. Increase of photovoltage on Te doping and a decrease on Zn doping is observed. The effect of phase transition, grain‐boundary potential barrier, and surface space charge on the photovoltaic effect are reviewed and studied. Analysis of different experimental results reveals that the generation of emf in angularly deposited films on an insulating surface is mainly due to formation of p‐n or p‐p+ junctions at the grain boundaries and the surface band bending.