K. K. Srivastava

Electrical properties of glassy AsxGe10Te90−x alloys

Abstract This paper analyses the electrical properties of glassy alloys of AsxGe10Te90−x, while reporting the conductivity and dielectric constant of As5Ge10Te85 and As15Ge10Te75 compositions in the temperature range 77–383 K and the frequency range from dc to 5 MHz. The dc conductivity has been shown to be of the form σ dc =σ0 1 exp (−δE 1 /kT) + σ0 2 exp (−δE 2 /kT The ratio σ01/σ02 is of the order of 106. ΔE1, the higher temperature activation energy, is dependent on the composition, while ΔE2, the lower temperature activation energy, is less dependent on the composition. The dielectric constant has been found to be independent of temperature and frequency up to about 253 K. However, at higher temperatures, it becomes activated and proportional to log ω. Some common features of AsxGe10Te90−x are a kink in dc conductivity, a ω0.8 relationship for ac conductivity, no evidence of variable-range hopping at low temperatures, field-dependent conductivity and memory switching. The data can be interpreted in terms of the dangling-bond theory of Mott and his collaborators. A high density of states of the order of 1020eV−1 cm−3 near the Fermi level may be expected.

Photoelectrical properties of AgInTe2

Abstract This paper reports on the photoelectrical properties of AgInTe2 through measurements of the ‘transient’ and ‘steady-state’ photocurrents. The material displayed great sensitivity to optical and thermal stresses. The ac. response of the material under dark and illuminated conditions was also investigated through measurements of the capacitance and a.c. conductance over a frequency range 5 Hz-1 MHz at different temperatures and illumination levels. An analysis of experimental results indicated the existence of a wide distribution of gap states. Under all conditions of a.c. and d.c. operation, the photo-induced responses were fast at the beginning and, thereafter, the rise and decay processes became slow with respect to time. The present authors propose a simple analysis to study the initial fast response in terms of the RC time constant of the sample system. The versatility of Elliotts correlated barrier-hopping model is also demonstrated through measurements of light-induced variations in capacit...

Complex impedance and dipolar behaviour of a silver-doped chalcogenide

Abstract In this paper we report new measurements of the complex impedance for silver-doped samples of a-Ge17Te83. Measurements were made on bulk samples (both undoped and silver doped) at different temperatures and at different bias voltages over a frequency range 5 Hz-100kHz using a computer-controlled a.c. system for measuring impedance and capacitance-voltage. The impedance of the undoped sample displayed insensitivity to temperature, frequency and voltage. On doping, a drastic change in impedance parameters was observed. The resistance and capacitance of the doped sample not only increased by many orders of magnitude but also displayed great sensitivity to external stresses such as temperature and voltage. The analysis of experimental results suggests that the silver-doped Ge17Te83 is basically a dipolar system. The simple dipolar model that we proposed successfully explains the experimental data reported in the paper.

Electrical and dielectric properties of As10Ge15Te75Ag x glasses

Abstract This paper analyses the effect of the addition of varying amounts of silver in concentrations from 0 to 10.0 at.% to As10Ge15Te75 glass on d.c. and a.c. conductivities, dielectric constant and various allied parameters in the temperature range 83-383 K and the frequency range from d.c. to 50 MHz. The activation energy of d.c. conductivity increases with silver content up to 1.0 at.% and shows a reversal in the trend with higher percentages (5.0 and 10.0 at.%). The a.c. conductivity and memory switching behaviour are not altered by the addition of silver. The dielectric data suggest a dipole-type relaxation mechanism. The dielectric data corroborate the observed conductivity data in suggesting a probable increase in Te-chain breakages leading to an increase in the number of charged dangling bonds with silver content up to 1.0 at.% and, at higher percentages of silver, alloy formation occurs resulting in the reversal of the trend. Most of the data can be explained by the ‘charged dangling bond’ mod...

Use of AgInTe2 for optoelectronic switching at higher frequencies

A possible application of AgInTe2 for optoelectronic switching is reported. Alternating and direct current (a.c. and d.c.) response of the material has been studied over a wide frequency range (5 Hz to 1 MHz) through measurements of conductance, capacitance and photocurrent at different temperature and illumination levels. The switching/recovery time has been analysed in terms of time constant τ and found to be of the order of microseconds for this material. Higher frequencies of operation (>40 kHz) are preferable because, at such frequencies, τ becomes almost independent of illumination level and temperature. Furthermore, the switching speed can be conveniently controlled with d.c. bias applied across the sample. Elliotts CBH model has been satisfactorily used to explain the switching behaviour for AgInTe2.

Silver-doping effects on electrical properties of Ge-Te alloy

Measurements showing that the electrical properties of Ge17 Te83 are drastically changed when it is doped with silver are reported. The pure material acts as a linear element whose a.c. impedance and phase angle were found to be invariant over a wide frequency range 10−3 to 105 Hz. On doping with silver, the sample displayed considerably higher values of a.c. impedance, capacitance and d.c. resistance than those shown by the pure material. The silver-doped system also showed non-linearI–V characteristics and a voltage-dependent capacitance. The change in electrical properties is explained using the dipolar model proposed. It is also shown that correlated barrier hopping model is applicable to the silver-doped chalcogenide and that the dipolar model is consistent with this model.

The CBH model applied to a.c. conductivity measurements at microwave frequencies for As2Se3

Abstract This paper reports measurements of the dielectric constant, dielectric loss and a.c. conductivity (σa.c.) for bulk samples of As2Se3 at different temperatures and frequencies ranging from 8 to 12 GHz. The study offers some new results to support the validity of the correlated barrier hopping (CBH) model for a.c. conduction in the microwave range. Our measurements provide explicit evidence to show that σa.c. saturates at 8 GHz, and a conversion of some of the bipolaron states into single-polaron states possibly takes place at higher temperatures. An attempt has also been made to calculate the hopping distance R and the mean intersite separation R s, to check whether the magnitude of R is not only smaller but also comparable to the magnitude of R s, because the CBH model assumes that the hopping of carriers remains confined to within a pair of sites.

Device applications of a new sensing material

Abstract The characteristics of an amorphous semiconducting alloy, Ge 17 Te 83 , change drastically when the material is doped with silver. The silver-doped system so formed makes a unique device which can be used as a versatile sensor, i.e. a voltage-dependent capacitor (VDC), a voltage-dependent resistor (VDR) or a temperature-dependent resistor (TDR). The VDC operation is preferable at higher frequencies ( > 10 kHz), whereas VDR and TDR devices are sensitive at lower frequencies (