A generalized analytical model based on multistage scattering phenomena for estimating the impact ionization rate of charge carriers in semiconductors

A generalized analytical model based on multistage scattering phenomena has been developed in this paper for estimating the impact ionization rate of charge carriers in semiconductors. The probabilities of impact ionization initiated by electrons and holes have been calculated separately by taking into account all possible combinations of optical phonon scattering and carrier-carrier collisions prior to the impact ionization. Finally the analytical expressions of impact ionization rate of electrons and holes have been developed by using the aforementioned impact ionization probabilities. The impact ionization rates of electrons and holes in 4H-SiC have been calculated within the field range of \(2.5\times 10^{8}\) – \(6.5\times 10^{8}\hbox { V m}^{-1}\) by using the analytical expressions of those developed in the present paper. Those are also calculated by using the analytical expressions developed by some other researchers earlier without considering the multistage scattering phenomena. Finally the theoretical results obtained from the analytical model proposed in this paper and the analytical model developed by earlier researchers within the field range under consideration have been compared with the ionization rate values calculated by using the empirical relations fitted from the experimentally measured data. Closer agreement with the experimental data has been achieved when the impact ionization rate of charge carriers in 4H-SiC are calculated from the proposed model as compared to the earlier one.     

Optical control of large-signal properties of millimeter-wave and sub-millimeter-wave DDR Si IMPATTs

The authors have proposed a complete large-signal (L-S) model to investigate the optical modulation of high frequency properties of double-drift region (DDR) impact avalanche transit time (IMPATT) devices operating at different millimeter-wave and sub-millimeter-wave frequencies. Simulation is carried out based on the proposed model to study the effect of photo-irradiation of different values of incident optical power of different wavelengths from 600–1000 nm on the DC and L-S characteristics of DDR IMPATTs based on Si designed to operate at 94, 140, 220, 300 and 500 GHz. Two different optical illumination configurations such as top mount and flip chip are taken into account for the present study. Results show that the maximum optical tuning of L-S parameters of the device can be achieved for optical illumination of wavelength 700 nm, i.e. near the wavelength corresponding to the responsivity peak of Si in both top mount and flip chip configurations. Further, better photo-sensitivity of top mount structure is observed as compared to its flip chip counterpart. The simulation results are found to be in good agreement with the experimental results reported earlier. Suitable tunable light source information is also suggested to carry out the optical control experiment within the wavelength range under consideration.     

Mapping software: Are we nearing standardization?

As software technologies advance, the software community uses the newest and most powerful technology and associated notations. However, mapping software with a set of notations that would survive the test of time is becoming increasingly difficult. A survey of current methodologies indicates that half‐lives of various software notations are short. The dependence of software notations on programming languages and environment specific methodologies often makes these notations obsolete. In this paper, development of a standard set of software notations that is independent of programming paradigms, yet extensible enough to accommodate programming needs, is proposed. This revised version was published online in June 2006 with corrections to the Cover Date.     

A path-sum Monte Carlo approach for many-electron systems within a tight-binding basis

We present a Path-Sum Monte Carlo method, a tight-biding approach to Path Integral Monte Carlo, as an alternative to mean-field theory for analyzing exchange-correlation effects in many-electrons systems. To test the algorithm we apply it to a small trial system of either four or six electrons confined to two parallel six single-orbital-atom rings (12 atoms and orbitals total) for which exact results are available for comparison. We observe the phase diagram for exciton formation as a function of interlayer separation and temperature, showing good agreement between the Monte Carlo and exact calculations. Moreover, although the Monte Carlo algorithm employs a fixed node approximation to avoid the Fermion sign problem and, therefore, is inexact, we consider two different limits to the fixed node approximation which provide upper and lower bounds on the total energy. While a simple system is considered here to allow the comparison with exact results, the algorithm should extend the reach of computational analysis to larger many-electrons systems such as, e.g., paired graphene layers for which room-temperature superfluidity has been predicted elsewhere.     

Fiber optic photoluminescence setup for spatially resolvedmeasurements

Spatially resolved photoluminescence is used as a nondestructive tool to characterize semiconductor epitaxial wafers with a resolution better than the device dimensions. In this paper, we describe a novel photoluminescence measurement setup using fiber optic techniques for luminescence excitation and detection in a very simple confocal arrangement. A final spatial resolution as small as 5 μm±0.5 μm together with the compact design makes it very attractive     

Association between some planktonic species and physicochemical characteristics of the water of Loktak Lake,Manipur, India

Four‐hourly data were collected for 24 hour periods in the months of December (1977), April (1978), July (1978) and December (1978) in respect of some physicochemical characteristics and plankton population in a protected part of the Loktak Lake (Manipur) India. Highly significant correlations, positive as well as negative, were observed between the diurnal and seasonal variations of physicochemical characteristics with those of total phyto or zooplankton of certain species.     

6—THE VARIATION OF FIBRE LENGTH IN JUTE-YARN SECTIONS OF VARYING THICKNESS AND ITS POSSIBLE RÔLE IN CONTROLLING THE UNEVENNESS OF YARN CAUSED BY DRAFTING

A study is reported of the average length of fibres crossing sections of different thickness in jute yarns of varying quality. The fibre length is shown to increase with a decrease in the thickness of yarn sections of all qualities. The need for standardization of the thickness of yarn sections in determining the average fibre length is stressed. On the basis of the results obtained, a possible explanation is suggested for the difference observed between cotton and man-made-fibre yarns on the one hand and jute and worsted yarns on the other with regard to the variations in unevenness with the number of fibres per cross-section.     

Mechanical properties of very thin cover slip glass disk

The biaxial flexural strength, Young’s modulus, Vicker’s microhardness and fracture toughness data for very thin, commercial, soda-lime-silica cover slip glass (diameter, D-18 mm, thickness, T-0.3 mm; T/D ≈ 0.02) are reported here. The ball on ring biaxial flexure tests were conducted at room temperature as a function of the support ring diameter (≈ 10–20 mm) and cross head speed (0.1–10 mm min⁻¹). In addition, the Weibull modulus data were also determined. The Young’s modulus data was measured using a linear variable differential transformer (LVDT) from biaxial flexure tests and was checked out to be comparable to the data obtained independently from the ultrasonic time of flight measurement using a 15 MHz transducer. The microhardness data was obtained for the applied load range of 0.1–20 N. The fracture toughnessK _IC data was obtained by the indentation technique at an applied load of 20 N.