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In this article, we studied intensity dependent third order nonlinear optical response in ternary As40Sb7Se53 and As40Sb10Se50 chalcogenide glasses by employing the nanosecond Z-scan technique. At low intensities, we observed saturable absorption in As40Sb7Se53 which makes a remarkable transition to reverse saturable absorption at higher intensities. On the other hand, when the Sb concentration increased in As40Sb10Se50, saturable absorption disappears and the sample exhibits only two-photon absorption. Experimental results further indicate that the strong two-photon absorption in our samples can be exploited to fabricate high performance solid state optical limiting devices for the next generation all-optical network. [ABSTRACT FROM AUTHOR]

In the present work we have reported the results of investigations on local structures of e-beam evaporated (Gd2O3-SiO2) composite thin films by synchrotron based EXAFS measurements. The evolution of local structure in the case of the Gd2O3-SiO2 system is found to be different from the HfO2-SiO2 system reported by us earlier. The EXAFS analysis has shown that the Gd-O bond length decreases monotonically as SiO2 content in the films increases. Also the amplitudes of the peaks in the FT-EXAFS spectra of the samples, which depend jointly on the coordination numbers as well as the Debye-Waller factors (measure of disorder) are found to decrease monotonically with increase in SiO2 contents in the Gd2O3 matrix. Atomic force microscopy (AFM) measurements of the samples also show continuous evolution of amorphous-like denser microstructure with increase in SiO2 content in the films. Hence incorporation of SiO2 in the Gd2O3 matrix, results in a continuous change in oxygen coordination yielding a change in the Gd-O bond length and also results in a continuous increase in amorphousness and a smoother morphology of the samples and, unlike the HfO2-SiO2 system, does not show any maximum for a particular SiO2 concentration. [ABSTRACT FROM AUTHOR]

In this paper, we present our studies on current-voltage characteristics due to tunneling in nonuniform and asymmetric multiple quantum well (MQW) structures. First, the transmission coefficient is calculated by solving the Schrödinger equation with the piecewise-constant potential approximation and by considering the effects of nonuniformity and the asymmetry of layer dimensions and band-offsets. Then the tunneling current through the structure is calculated as a function of bias for different structural combinations of the MQW structure. The configurations suitable for some applications are indicated in the results. [ABSTRACT FROM AUTHOR]

In the present work we have reported the results of investigations on local structures of e-beam evaporated (HfO2–SiO2) composite thin films by synchrotron based extended x-ray absorption fine structure measurements. It has been observed that for the composite film with 10% SiO2 content, both Hf–O and Hf–Hf bond lengths are less than their values in pure HfO2 film. However the bond lengths subsequently increase to higher values as the SiO2 content in the composite films is increased further. It has also been observed that at the same composition of 10% SiO2 content, the films have smallest grain sizes (as obtained from atomic force microscopy measurements) and highest refractive index (as obtained from spectroscopic ellipsometry (SE) measurements) which suggests that the e-beam evaporated HfO2–SiO2 composite films with 10% SiO2 content leads to the most compact amorphous thin film structure. [ABSTRACT FROM AUTHOR]

In this paper, the responsivity of a resonant-cavity-enhanced SiGe/Si multiple quantum well photodetector has been theoretically investigated. The present model considers the effects of material parameters of Si1-xGex and recombination of carriers confined by the potential barriers at the heterointerfaces of Si1-xGex/Si quantum wells on the detector responsivity for different Ge-contents (x). The effect of electric field due to applied bias on the emission of confined carriers from quantized subbands has also been included in the analysis. Results show that though high Ge-content is required to enhance the responsivity of the SiGe/Si photodetector for long-haul communication (at 1.3 and 1.55 μm), the confinement of holes at the heterointerfaces may be significant to affect the responsivity adversely. Studies at 1.3 and 1.55 μm also show that the responsivity of the photodetector for a particular Ge-content in the active layer can be increased by suitable choice of well parameters and applied bias. [ABSTRACT FROM AUTHOR]

In this paper, the intersubband transition energy in an n-type semiconductor quantum ring has been investigated in the presence of an electric field perpendicular to the plane of the ring. The analysis has been done considering the effect of band nonparabolicity of the semiconductor. The results show that at high electric field energy varies nonlinearly with field and the optical transition between the two lowest quantized subbands can be controlled by the electric field. It has also been shown how this fine wavelength tuning by electric field depends on the band gap of the semiconductor. [ABSTRACT FROM AUTHOR]

We report results of a comprehensive study of the phase transition at TN (∼643 K) as a function of particle size in multiferroic BiFeO3 system. We employed electrical, thermal, and temperature dependent x-ray diffraction studies in order to characterize the transition in a host of samples. We also carried out detailed magnetic measurements over a temperature regime of 2–300 K under a magnetic field of 100–10 000 Oe both on bulk and nanocrystalline systems. While in the bulk system a sharp endothermic peak at TN together with a broad feature, ranging over nearly ∼100 K (ΔT), could be observed in calorimetry, the nanoscale systems exhibit only the broad feature. The characteristic dielectric anomaly, expected at TN, is found to occur both at TO and TN across ΔT in the bulk sample. The Maxwell-Wagner component due to interfaces between heterogenous regions with different conductivities is also present. The magnetic properties, measured at lower temperature, corroborate our observations in calorimetry. The metastability increases in the nanoscale BiFeO3 with divergence between zero-field cooled and field cooled magnetizations below ∼100 K and faster magnetic relaxation. Interestingly, in nanoscale BiFeO3 one also observes finite coercivity at lower temperature, which points out that suitable design of particle size and shape may induce ferromagnetism. The inhomogeneous distribution of Bi/Fe ions and/or oxygen nonstoichiometry seems to be giving rise to broad features in thermal, magnetic as well as electrical responses. [ABSTRACT FROM AUTHOR]

In this article the frequency response of a resonant-cavity-enhanced (RCE) separate absorption, grading, charge, and multiplication (SAGCM) avalanche photodiode (APD) has been investigated. This study on APDs includes the development of a model for the avalanche buildup of carriers including the dead-space effect. In this model, the carriers are characterized by their energy and position in the region of multiplication. The excess energy of the carriers above threshold are assumed to be equally distributed among the carriers after impact ionization. The analysis shown in this article can be used to study the frequency response of the APD for a wide range of reverse bias voltages. For low bias voltages, an analytical expression has been derived to study the emission of carriers from the interface trap. The delay due to diffusion of photogenerated carriers from the undepleted region of the absorption layer and the low velocity of carriers at low field have also been considered. The model is used to calculate gains at different biases and bandwidth at different dc gains. The results show good agreement with published experimental data on a RCE SA(G)CM APD. [ABSTRACT FROM AUTHOR]

The results of a comprehensive study carried out both on bulk and nanoscale BiFe[O.sub.3] for exploring the phase transition features near [T.sub.N] as well as the low temperatures magnetic properties are reported. The ferromagnetism and finite coercivity is observed at lower temperature in nanoscale, which has resulted from enhanced lattice strain.

Presents information on a study wherein interface traps are created in metal-oxide-semiconductor field-effect transistors when hot carrier stressing is done with the maximum substrate current biasing condition. Methods; Results; Discussion.

Presents information on a study which examined the effects of gamma ray irradiation on gate induced drain leakage current in metal oxide semiconductor transistors. Background of the study; Methodology of the study; Results and discussion.

We report results of a comprehensive study of the phase transition at TN (∼643 K) as a function of particle size in multiferroic BiFeO3 system. We employed electrical, thermal, and temperature dependent x-ray diffraction studies in order to characterize the transition in a host of samples. We also carried out detailed magnetic measurements over a temperature regime of 2–300 K under a magnetic field of 100–10 000 Oe both on bulk and nanocrystalline systems. While in the bulk system a sharp endothermic peak at TN together with a broad feature, ranging over nearly ∼100 K (ΔT), could be observed in calorimetry, the nanoscale systems exhibit only the broad feature. The characteristic dielectric anomaly, expected at TN, is found to occur both at TO and TN across ΔT in the bulk sample. The Maxwell-Wagner component due to interfaces between heterogenous regions with different conductivities is also present. The magnetic properties, measured at lower temperature, corroborate our observations in calorimetry. The metastability increases in the nanoscale BiFeO3 with divergence between zero-field cooled and field cooled magnetizations below ∼100 K and faster magnetic relaxation. Interestingly, in nanoscale BiFeO3 one also observes finite coercivity at lower temperature, which points out that suitable design of particle size and shape may induce ferromagnetism. The inhomogeneous distribution of Bi/Fe ions and/or oxygen nonstoichiometry seems to be giving rise to broad features in thermal, magnetic as well as electrical responses. [ABSTRACT FROM AUTHOR]