N. Kishore

Temperature and frequency dependent conductivity of bismuth zinc vanadate semiconducting glassy system

The ac conductivity of bismuth zinc vanadate glasses with compositions 50V2O5. xBi2O3. (50-x) ZnO has been studied in the frequency range 10−1 Hz to 2 MHz and in temperature range 333.16 K to 533.16 K. The temperature and frequency dependent conductivity is found to obey Jonschers universal power law for all the compositions of bismuth zinc vanadate glass system. The dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of experimental data of ac conductivity with Jonschers universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating center (Hf) and enthalpy of migration (Hm) have also been estimated. It has been observed that mobility of charge carriers and ac conductivity in case of zinc vanadate glass system increases with increase in Bi2O3 content. In order to determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed in the frame work of various theore...

Hopping conduction in bismuth modified zinc vanadate glasses: An applicability of Mott's model

The dc conductivity measured in a wide range of temperatures (room temperature to 533.16 K) for glass samples of compositions 50V2O5·xBi2O3·(50-x) ZnO; x = 0, 5, 10, 15, and 20, is discussed in this paper. The temperature dependent dc conductivity has been analyzed in the framework of various theoretical models, which describe the hopping conduction in disordered semiconducting systems. It has been observed that Motts model of polaron hopping in transition metals is in good agreement with the experimental data in high as well as intermediate temperature regions. The various polaron hopping parameters have also been deduced. It has been ascertained by these estimated quantities and different approaches that the electrical conduction in present glass system is due to non-adiabatic variable range hopping of small polarons. Moreover, it has been found that Motts and Greaves’ variable range hopping models are in good agreement with the experimental data in the whole studied temperature range in the present i...

Electronic conduction in vitreous semiconductors in the pseudo-binary system (As2S3)1-x(PbS)x

AC conductivity and dielectric relaxation measurements of the bulk amorphous compositions in the pseudo-binary system (As2S3)1-x(PbS)x (x = 0, 0.1, 0.4 and 0.5) in the frequency range 500 Hz-10 kHz and in the temperature span 180–450 K are reported. The temperature dependence of the ac conductivity, σac(ω), has a broad structure at all frequencies in compositions with x = 0.1, 0.4 and 0.5 whose peak position is not thermally activated. A similar structure was also observed in the data on the dielectric constant, ϵ1, which peaked at a frequency of 1 kHz in the composition with x = 0.5. Analysis of the results using the correlated barrier hopping model revealed that the electronic conduction takes place by single polaron and bipolaron hopping processes at high and low temperatures, respectively, in compositions containing Pb. The microstructure and phase-separation in the glasses containing Pb influence the electrical transport and dielectric dispersion. This study has revealed the possible presence of a phase transformation at around 300 K at a frequency of 1 kHz in the dielectric dispersion behaviour of composition with x = 0.5.

Effect of addition of Zn impurities on the electronic conduction in semiconducting Se80-xTe20Znx glasses

Abstract A study of the effect of the addition of Zn impurities on the electronic transport properties of melt-quenched semiconducting glasses in the system Se80-xTe20Znx (x = 0, 1, 2 and 4) has been undertaken for the first time. Measurements of the temperature dependence of the d.c. conductivity and the frequency and temperature dependence of the d.c. conductivity [sgrave]a.c.(ω) and dielectric relaxation have been made in the temperature interval 180–450 K and frequency range 500 Hz–10 kHz. It is revealed that [sgrave]a.c.(ω) is proportional to ω s . The temperature dependence of [sgrave]a.c.(ω) and the parameter s is reasonably interpreted by the correlated-barrier-hopping model. The analysis of the results shows that the electronic conduction in compositions with x = 0 and 1 takes place by a bipolaron-hopping process in the whole temperature range of study. The addition of higher concentrations of Zn impurities (x = 2 and 4) induces new types of defects which contribute predominantly to single-polaro...

Optical study of MeV energy heavy ion-induced effects in crystalline germanium and silicon

Abstract An optical study of Ni-ion (60 and 75 MeV) bombarded polished single crystals of Ge (〈111〉), Sb-doped, 1 Ω cm) and Si (〈111〉, intrinsic) at room temperature with fluence ranging from 1 × 10 13 to 1 × 10 15 ions/cm 2 has been carried out in the spectral regions of the fundamental optical absorption edge and interband transition. The damage inflicted by the MeV energy ion on the surface and deep inside the bulk of the semiconductors has been monitored by determining the dose dependence of optical constants α , R and n in the spectral range 200–2500 nm. Analysis of the results reveals that electronic energy loss arising out of the inelastic ionising collisions of swift heavy ions, in addition to the nuclear energy loss, influence the surface and the bulk properties of the bombarded semiconductors. Formation of divacancies in the bombarded Si is supported by the appearance of an absorption band at around 0.7 eV. The surface effects of ion-implantation at MeV energy are quite different from those at keV energy.

Electrical and optical properties of thermally evaporated thin films of (As2S3)1−x(PbS)x

Abstract An investigation of the electrical and optical properties of amorphous thin films of alloys in the pseudo-binary system (As2S3)1−x(PbS)x (x = 0, 0.1, 0.4 and 0.5) prepared by flash evaporation has been carried out. The synthesized films were characterized by X-ray diffraction, electron spectroscopy for chemical analysis and scanning electron microscopy techniques. The study shows that the stoichiometric composition (x = 0.5 ) exhibits electronic properties which are quite different from those of the other compositions. The optical energy gap decreases with the addition of PbS. The electrical transport takes place predominantly in the extended states. The alternating current (a.c.) conductivity results show that, at lower temperatures, conduction occurs via bipolaron hopping, while, at higher temperatures, it predominantly takes place by single polaron hopping. In contrast to the bulk glasses, no broad peak is observed in the temperature dependence of the a.c. conductivity of the thin films. The thin films appear to be homogeneous, while the corresponding bulk compositions show phase separation. The structural and electronic features of these semiconductors arc affected by the increasing Pb coordination number with the increase in the PbS content; the coordination number is 9 in the composition with x = 0.5.

Electronic conduction in Pb-modified amorphous semiconductors Pb20GexSe80-x exhibiting a p-n transition

Abstract A.c. conductivity and dielectric relaxation studies of Pb-modified amorphous semiconductors Pb20GexSe80-x, exhibiting a p-n transition at x = 21, are reported as functions of frequency in the range 100Hz-10kHz and as functions of temperature in the range 180–450 K. The a.c. conductivity σa.c(ω) is found to be proportional to ω5. The temperature dependence of σa.c (ω) and of the exponent s for all the compositions examined have been interpreted using the correlated-barrier-hopping model. Analysis of the results reveals that electronic conduction in GeSe3·5 takes place via bipolaron hopping in the whole temperature range of study. The addition of Pb impurities induces new types of defect (C1 1 and Pb2+) which contribute predominantly to single-polaron hopping at higher temperatures. However, the conduction at lower temperatures is of bipolaron type in compositions with or without Pb. Strong temperature and frequency dependences of the loss tangent tan δ at higher temperatures in the compositions co...

Structural, optical, electrical, and magnetic properties of Zn0.7MnxNi0.3−xO nanoparticles synthesized by sol–gel technique

Abstract The structural, morphology, optical, electrical, and magnetic properties of Zn0.7MnxNi0.3−xO (x = 0.05, 0.1, 0.15, 0.2) nanoparticles synthesized by sol–gel technique have been systematically investigated by using X-ray diffractometer (XRD), scanning electron microscope (SEM), UV–vis-NIR spectrophotometer, impedance analyzer, and vibration sample magnetometer (VSM). XRD patterns reveal that all samples have hexagonal wurtzite structure along with secondary phases such as NiO and ZnMnO3. The average crystalline size increases with the increase in the Mn concentration in the host matrix. Diffuse reflectance studies (DRS) show an increment in optical band gap with increasing Mn content. AC conductivity of present samples has been studied as a function of frequency (100 Hz–10 MHz) of the applied AC signal in the temperature range of 323–463 K. The results showed that AC conductivity increases with an increase in frequency and temperature. The frequency exponent shows that small polaron conduction mechanism is the most favorable for all samples. The value of AC conductivity is observed to decrease with an increase in the Mn dopant concentration in the Zn0.7MnxNi0.3−xO system. At room temperature, magnetic characterization of the samples indicates the presence of both paramagnetic and ferromagnetic behavior. Magnetic saturation decreases with the increase in the Mn concentration in the host lattice.

Uranium quantification in groundwater and health risk from its ingestion in Haryana, India

Uranium is a naturally occurring radioactive element which may cause toxicological or radiological hazards to the public if present in drinking water. This study reports the quantification of uranium in groundwater of major towns of the district Fatehabad, Haryana, India. Uranium concentrations ranged between 0.3 and 48 μg L−1. In 22% of the groundwater samples, uranium concentrations were higher than the World Health Organization maximum permissible limit of 30 µg L−1. The radiological dose for males was found to be in the range of 4.8 × 10−4–7.1 × 10−2 mSv y−1 and for females 3.5 × 10−4–5.2 × 10−2 mSv y−1. The results showed that due to the ingestion of groundwater in the study area, radiological cancer risk is in the range of 9.1 × 10−7–1.3 × 10−4, lower than the risk limit. Uranium ingestion from groundwater varied from 0.02 to 3.5 µg kg−1 day−1, which is within acceptable limit.

Study of the effect of thermal annealing on the optical and electrical properties of vacuum evaporated amorphous thin films in the system Ge20Te80-xBix

We systematically studied the effect of thermal annealing on the optical and electrical properties of amorphous semiconducting thin films in the system Ge20Te80−xBix (x = 0, 0.19, 2.93, 7.35) prepared by flash evaporation in a vacuum of 1 × 10−6 Torr. The films are characterized by x-ray diffraction (XRD) and electron probe micro analysis. The annealing temperature is kept at 150 °C, 180 °C and 220 °C. No crystallization of the thin films is achieved on annealing up to the temperature of 150 °C. At a higher temperature of annealing, microcrystals of Te, Bi2Te3, Ge–Te, etc, are observed along with an amorphous phase as indicated by XRD analysis. The fundamental optical absorption edge and reflection spectra of as-prepared and annealed films are determined. Optical interband transitions are observed for various films (as-prepared and annealed). The presence of crystalline Bi2Te3 in films annealed at 220 °C is also supported by the reflection spectrum. The optical energy gap (Eg), the slope parameter (Δ) of the absorption edge and the tailing parameter (B−1) of the energy band tails are computed from the optical data. The dc electrical conductivity (σdc) of various films is studied in the temperature range of 150–450 K. We observe that two types of conduction take place: conduction through extended states in the higher temperature region, and conduction through localized states in the band tails and at the Fermi level by the hopping process assisted by phonons at lower temperatures. The data at higher temperatures have been fitted with the expression σdc = σ0exp(−ΔE/kT) and the electrical parameters, ΔE and σ0, are also determined. It is observed that the bismuth concentration and annealing temperature dependences of the optical and electrical parameters are different in the two regions of compositions, x ≤ 2.93 and x > 2.93, indicating structural differences in the two sets of compositions. It is pointed out that the bulk form of these amorphous semiconductors exhibits a carrier sign reversal at a bismuth concentration of about 3.5 at%. However, the thin-film form of these amorphous semiconductors does not show such a carrier sign reversal in the electrical transport.