P. C. Mathur

Electrical and optical properties of Ge20SbxSe80−x thin films

Abstract The mechanism of incorporation of metallic antimony in amorphous films of the Ge 20 Sb x Se 80−x (5⩽ X ⩽25) system is studied by measuring the d.c. conductivity and optical absorption. It is observed that the addition of antimony increases the d.c. conductivity and decreases the optical gap of the system. The d.c. conductivity variation over the measured compositional range is analysed using the chemically ordered network model, which forms the microscopic molecular species of the system. An exponential dependence of the pre-exponential factor on activation energy is interpreted on the basis of the Meyer-Neldel rule. The change in the optical gap associated with antimony doping is explained in terms of defect states.

n-Type conduction in Pb doped Se–In chalcogenide glasses

This paper reports on the p to n transition in Pb doped Se–In chalcogenide glasses. Measurements of thermoelectric power in the temperature range 300 K⩽T⩽315 K, dc conductivity in the temperature range 100⩽T⩽300 K, and optical band gap (Egopt) have been carried out for Se75In25−xPbx (x=0,5,10,15) samples. The p-n transition occurs with very low addition of Pb impurity (5 at. %). The conductivity and pre-exponential factor also change by five to six orders of magnitude with Pb doping. Results are explained on the basis of the formation of ionic Pb–Se bonds, instead of covalent bonds. Formation of ionic bonds disturbs the equilibrium between the charged defect states of Se–In glass and unpins the Fermi level and thus leads to n-type conduction in these glasses.

A.c. conduction in the amorphous Ge—Sb—Se system

Abstract A.c. and d.c. conductivities of amorphous films of Ge—Sb–Se have been investigated for different Sb: Se ratios, keeping the Ge content constant at 20 at. %. The a.c. conductivity [sgrave](ω, T) in the frequency range 0•5-10•0 kHz is found to obey the law [sgrave](ω, T) = Aω3. The exponent s is found to decrease with increasing temperature and Sb content, which is inconsistent with the quantum-mechanical tunnelling model. A strong temperature dependence of the a.c. conductivity [sgrave](ω, T) and exponent s in the entire range of temperatures and frequencies is reasonably interpreted by the correlated barrier hopping model, taking into account the contribution of both single polarons and bipolarons. The values of the energy of bound states, the correlation energy and the Fermi energy are estimated from the best fit between theoretical and experimental results. It is observed that the correlation energy increases while the energy of bound states decreases with increasing Sb content. The decrease in...

Effect of laser irradiation on structural, electrical and optical properties of SnO2 films

Thin films of SnO2 were prepared using a spray pyrolysis technique. Films were irradiated with Nd:YAG laser pulses of various energy densities (2–50 mJ cm−2) with varying number of pulses from 1–50. X-ray diffraction studies were made to investigate the structural changes due to laser irradiation. An improvement in crystallinity and an increase in grain size were observed in laser-irradiated films. Hall coefficient and Hall mobility studies were made in the temperature range 77–300 K for the as-grown as well as laser-irradiated films. An increase in mobility and a decrease in carrier concentration were observed in the films after laser irradiation. Optical transmission studies revealed that the refractive index increased as a result of laser irradiation.

ELECTRICAL AND OPTICAL PROPERTIES OF AMORPHOUS (SE0.7TE0.3)100-XINX SYSTEM

The effect of In impurity on the dark and photoconductivity and the optical band gap of amorphous (Se0.7Te0.3)100−xInx has been studied. The activation energy ΔE and the pre‐exponential factor σ0(0,T) which appear in the dc conductivity are found to increase with increasing In content. The photocurrent, as a function of illumination intensity and time of illumination, has been measured at around room temperature. The bimolecular recombination mechanism is found to be predominant at steady state in all the samples near room temperature. The nonexponential decay, after stopping the illumination, has been explained in terms of localized‐localized recombination. The data have been analyzed in terms of the dispersive diffusion controlled recombination and monomolecular recombination is found to be dominant in the transient state. The optical band gap is found to decrease with increasing In content. This decrease has been explained on the basis of metallic bonding due to incorporation of In.

Influence of anodisation time, current density and electrolyte concentration on the photoconductivity spectra of porous silicon

Abstract Porous silicon layers emitting red photoluminescence (PL) have been prepared by the anodisation of p-type 〈100〉 monocrystalline Si substrate in different HF concentrations. The steady state photoconductivity of porous silicon (PS) layers as a function of electrolyte concentration, anodisation time and current density has been studied. The photoconductivity (PC) peak was observed to shift towards the shorter wavelength with the decrease in the crystallite size and it was interpreted to be the result of band gap widening. The recombination is found to have contribution from both the monomolecular and the bimolecular processes.

Study of Se–Te–Sb System for Application to Reversible Optical Data Storage

In the present work variation of the two main parameters–viscosity and critical cooling rate, required for the recent upcoming optical data storage devices, have been analysed for different compositions of Se80-xSbxTe20 (0≤x≤9) system. Temperature dependence of viscosity has been determined using the activation energy for glass transition and for crystallization obtained from heating rate dependence of glass transition temperature and peak crystallization temperature from DSC measurements. Vicsocity has been estimated with the help of Vogel-Tamman-Fulcher equation. It has been found that for samples containing Sb≤4 at.%, the viscosity increases with the increase in Sb content. Further increase in Sb concentration causes a decrease in the viscosity. These results are consistent with the structural changes taking place in the Se–Te system with increase in Sb content. Using these values of viscosity and kinetics of crystal nucleation and growth process, the time-temperature-transformation curves were obtained. The critical cooling rate Rc is found to increase for Sb>4 at.%. For good reversible phase change optical recording, the critical cooling rate of the material should be high enough so as to get an erasure time of less than 1 µs. From the analysis of the data the suitability of the SeTeSb system for optical recording has been discussed.

Effect of laser irradiation on structural, electrical, and optical properties of p-mercury cadmium telluride

Single crystals of p‐Hc1−xCdxTe (x=0.16) were grown by the Bridgeman technique. The bulk single crystals were irradiated with laser pulse of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53 μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the Van der Pauw technique in the temperature range 77–300 K for both as‐grown and laser‐irradiated samples. Also the x‐ray diffraction pattern and transmission measurements of the samples were taken at room temperature. Electrical studies shows that the p‐mercury cadmium telluride after the laser irradiation becomes n type and optical results show that the free‐carrier concentration after laser irradiation increases sharply so that there is negligibly small transmission. The x‐ray studies show that single crystal p‐type samples after laser irradiation undergo structural changes as well, introducing ...

Effect of laser annealing on electrical and optical properties of n‐mercury cadmium telluride

Single crystals of n‐Hg1−xCdxTe (x=0.18) were grown by the Bridgman technique. The bulk single crystals were irradiated with laser pulses of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53‐μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the van der Pauw technique in the temperature range 77–300 K, for both as‐grown and laser‐irradiated samples. Also, transmission measurements of the samples were taken at room temperature. Both electrical and optical studies showed that laser irradiation introduces additional defects in mercury cadmium telluride (MCT), and its quality deteriorates instead of improving as observed in many other semiconductor materials. We found that laser irradiation increases free‐carrier concentration and decreases the band gap of MCT.

Fabrication of low resistive CdS thin films

Abstract Low resistive and high mobility thin films of CdS have been grown using vacuum evaporation techniques. X-ray diffraction studies show that the films are well oriented with a preferential growth of crystallites in the (002) plane. The value of conductivity observed in these films is in the range 0.088Ω -1 cm -1 −1.34Ω -1 cm -1 at 300 K.