P.C. Mathur

Thermoelectric power in porous silicon

Thermoelectric power measurements have been made on macroporous (pore width >500u2009A°) porous silicon samples prepared by an anodic dissolution technique. The sign of thermopower is found to be negative indicating that conduction takes place due to electrons in the conduction band. The conduction mechanism is found to be due to variable range hopping near the Fermi level for temperatures below 150 K. At higher temperatures the conduction is due to the tunneling of carriers in the localized states in the band edges. It was concluded that these localized states are formed because the nanocrystallites in porous silicon are randomly distributed in size and orientation leading to fluctuations in band gap. This results in the constitution of a disordered system on a macroscopic scale.

High Pressure Studies on n-Type Se–In–Pb Chalcogenide Glasses

The measurement of dc conductivity as a function of pressure in the range 0 ≤ P < 2.0 GPa for Se 75 In 25-x Pb x (x = 0, 5, 10, 15) glasses are reported. n-type Se-In-Pb glasses show a maximum in the resistance versus pressure. Differential Scanning Calorimetric (DSC) studies have also been carried out for the measurement of the glass transition temperature (T g ). The results have been explained in terms of the presence of fourfold coordinated Pb atoms in the Se-In host matrix.

A method for the calculation of the characteristic impedance of microstrip

A simple method has been reported for the estimation of the characteristic impedance of microstrip by evaluating the associated capacitances. These results are in good agreement with the experimental data.

Electron transport in porous silicon

Low field and high field DC conductivity measurements have been made on macroporous p-type porous silicon (PS) samples prepared by anodic dissolution. The conduction mechanism is found to be due to Variable Range Hopping near the Fermi level for temperatures below 150 K. At high temperatures the conduction is due to the tunneling of carriers in the localized states in the band edges near the valence band. The analysis of the data shows that PS presents a fractal structure between 1D and 2D systems.

Effect of sulfur doping on electrical conductivity of a-Si:H

Abstract The present paper reports the electrical conductivity and optical bandgap measurements of a-Si,S:H films in the alloy range (S/Si ratio 0.51 * 10 −2 to 4.07 * 10 −2 ) as a function of deposition temperature. The a-Si,S:H samples were prepared by conventional plasma-assisted CVD through decomposition of H 2 S and SiH 4 mixtures using substrate temperatures up to 500°C. When the deposition temperature is raised from 230 to 500°C, the concentration of S in the films decreases. The main effect of S alloying is a strong increase in IR mode at approximately 480 cm −1 which corresponds to Si S bond. The optical bandgap decreases dramatically with deposition temperature. The conductivity is found to be activated with the fermi level moving towards the conduction band edge up to S/Si ratio of 0.51 * 10 −2 and as the S/Si ratio further increases an increase in activation energy is observed which may be due to the increase in bandgap. The value of σ 0 indicates conduction in extended states.

Conduction mechanism in amorphous Si films

Abstract dc conductivity as a function of temperature has been measured for as-evaporated and annealed films of amorphous Si, grown by the vacuum evaporation technique. The experimental data suggest that conduction in the higher temperature range (∼175–300 K) is by the thermally activated holes in the localized states near the valence band edge while conduction in the lower temperature range (∼77–175 K) is found to be thermally assisted tunnelling in the localized states near the Fermi level. The activation energy for both the processes is found to increase with an increase in the annealing temperature. The average hopping distance, calculated for conduction near the Fermi level, is also found to increase with an increase in the annealing temperature.

Negative magnetoresistance of amorphous selenium and tellurium doped selenium

Abstract Negative magnetoresistance (MR) has been observed in bulk amorphous selenium and bulk tellurium doped selenium samples. The negative MR is found to decrease with tellurium doping. The experimental results are discussed in the light of various already existing models for negative MR.

Suitability of Ge-As-Te system for optical data storage

We report the study of crystallization kinetics and time-temperature-transformation in alloys of Ge7.5AsxTe92.5-x (x=20, 40, 45, 47.5, 50, 52.5, 55) and Ge10AsxTe90-x (x=15, 20, 22.5, 35, 40, 45, 50), in order to examine the suitability of these alloys for reversible phase change optical recording (RPCOR) films, which is one of the leading optical storage devices. Using the values of viscosity and kinetics of crystal nucleation and growth process, the time-temperature-transformation curves were obtained. The variation of critical parameters such as minimum erasure time and thermal stability has been calculated as a function of composition. It has been observed that for our samples, the critical cooling rate is high (2.1*105-4.3*104 K/min) for Ge10AsxTe90-x (x=15, 20, 22.5, 35, 40, 45, 50) and 1.51*105-2.91*104 K/min for Ge7.5AsxTe92.5-x (x=15, 20, 22.5, 35, 40, 45, 50) ensuring fast erasure speed ( approximately=1 mu s) which is an essential requirement for high quality RPCOR films. It is suggested that the material with lower concentration of Germanium (<10 at.%), Arsenide and Tellurium concentration between (35-55 at.%) are better contenders for the above application.

The influence of transverse magnetic field on Gunn effect threshold

Abstract The effect of magnetic field has been studied on the Gunn effect threshold electric field for short planar Gunn devices. For low magnetic fields, experimental results are in good agreement with the theoretical results but a large increase in threshold electric field has been observed for higher magnetic fields.

The effect of transverse magnetic field on resistively loaded Gunn diodes

Abstract The effect of transverse magnetic field has been studied on a resistively loaded diode. The peak to valley ratio of the current and transit time of the domains is found to increase with the magnetic field.