Nickel-Dopant Atom Clusters and their Effect on the Recombination Properties of Silicon

The investigation determined the types and nature of structural defects in n-type silicon featuring nickel-dopant atom clusters by using deep-level transient spectroscopy (DLTS) and measuring specific resistance, concentration and lifetime of charge carriers. The investigation employed the Solver-NEXT infrared and atomic-force microscopes. We observed that after high-temperature diffusion star-like defects appear in those Si samples that were cooled slowly. Rapid cooling of Si samples yields no decorating of dislocations, which is linked to formation of [Ni-O]-type point defects, [Ni-Si] silicides and Ni[Nis-Nii] atom pairs (unlike in the case of slowly cooled doped Si samples). The differences in shape and size of the defects forming in slowly and rapidly cooled Si samples may be explained as follows: in the case of slow cooling, as the system transitions into the equilibrium state, its free energy decreases, and nickel atoms gradually precipitating at the defects of the crystal lattice form inclusions characterised by the most energetically favourable state, that is, star-like defects. We detected an increase in charge carrier lifetime caused by formation of a trapping level connected to the [Ni-O] complex in silicon

Gravity Waves in a Horizontal Shear Flow. Part I: Growth Mechanisms in the Absence of Potential Vorticity Perturbations

Interaction of internal gravity waves with a horizontal shear flow in the absence of potential vorticity perturbations is investigated making use of closed-form solutions. Localized wave packet trajectories are obtained, the energy growth mechanisms occurring are identified, and the potential role of perturbation growth in wave breaking is assessed. Regarding meridional propagation, the wave packet motion is limited by turning levels where the waves are reflected and trapping levels where the waves stagnate. Regarding perturbation energy amplification, two growth mechanisms can be distinguished: growth due to advection of zonal velocity and growth due to downgradient Reynolds stresses. The three-dimensional perturbations producing optimal energy growth reveal that these two mechanisms produce large and robust amplification of zonal velocity and/or density and vertical velocity, potentially leading to shear or convective instability. For large static stability, amplification of density perturbations in conjunction with vertical orientation of the constant phase lines close to the trapping level potentially leads to a convective collapse of the wave packet near the trapping level, in agreement with existing direct numerical simulation studies. For lower static stability and for waves with phase lines oriented horizontally, growth due to advection of zonal velocity dominates, leading to rapid growth of streamwise streaks within the localized wave packet and potentially to shear instability.

The Study on Charge-trapping Mechanism in Nitride Storage Flash Memory Device

In this work, the charge-trapping distributions of polysilicon-oxide-nitride-oxide-silicon (SONOS) structure are studied. The trapping energy level of SiNx films with different composition ratio deposited by low-pressure chemical vapor deposition (LPCVD) were first characterized by photoluminescence (PL) measurement. Moreover, using F-N/CHE program and charge pumping techniques, the vertical location and the lateral distribution of programmed charges are investigated in the nitride films with different composition ratio. The study offers strong evidence that the density of charge-trapping levels in the Si-rich nitride is higher than the standard nitride. A simple qualitative model and calculation explains that the trapping level distributions in the SiNx films are shallower by increasing relative Si-content. Furthermore, we have observed the nitride trap vertical location was changed by adjusted Si/N composition ratio. And the lateral distribution of hot electron programmed charges in the modified nitride is broader than that in the standard nitride because it offered more charge-trapping sites and shallower charge-trapping levels. In summary, the study can help researchers to understand the nitride charge-trapping mechanism and the analysis of optical/electrical characteristics.

Influence of iodine on the electrical properties of magnesium phthalocyanines thin film devices

The influence of iodine on the electrical properties of sandwich structures of magnesium phthalocyanine (Mg Pc) thin films with gold and aluminium electrodes has been investigated. The various electrical properties and different electrical parameters of the iodine-doped Mg Pc thin film devices have been estimated and compared with the values of normal Mg Pc devices from the analysis of the current-voltage characteristics. Generally samples showed an asymmetric conductivity both under forward and reverse bias. From our study we found that iodine doped Mg Pc films showed an enhanced electrical conductivity of nearly ten times that of typical Mg Pc. At low voltages the films showed an ohmic conduction with a hole concentration of P0 = 6.34 × 1018 m−3 and hole mobility μ = 9.16 × 10−5 m 2 V−1 s−1, whereas at higher voltage levels the conduction is dominated by space charged limited conduction (SCLC) with a discrete trapping level of 1.33 × 1022 m−3 at 0.63 eV above the valance band edge. The ratio of the free charges to trapped charges (trapping factor) for the doped samples was found to be 1.07 × 10−7. Furthermore the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident which was attributed to Poole-Frankel emission with a field-lowering coefficient of value 2.24 × 10−5 eV m1/2 V−1/2.

STUDY OF THE PRINCIPLES OF INNOVATION FOR THE BOP CONSUMER — THE CASE OF A RURAL WATER FILTER

It is now well known that the principles of innovation for the Bottom of the Pyramid (BOP) markets are different from those of the top of the pyramid. This paper discusses these principles taking the example of the development of a rural domestic water filter in India. Work related to two principles are highlighted, viz, product development based on deep understanding of functionality and price — performance focus. The former was achieved through the development of a realistic specification for the bacterial (Coliform) trapping level of filtered water by using DMAIC (Define, Measure, Analyze, Improve and Control) methodology. When the filters made by the villagers from the resulting process is introduced in a small village in India, significant reduction in the number of cases due to water-borne diseases is reported. The resulting reduction in medical costs is shown to far outweigh the initial and subsequent maintenance costs of the filter. A simple entrepreneurship model is outlined showing a win-win situation for the rural consumer as well as the rural entrepreneur.

Transient Photoconductivity of GaN Thin Film On Sapphire Substrate

ABSTRACTWe studied the transient photoconductivity(PC) properties of GaN thin film on (0001) sapphire substrate. The decay curves of PC obtained by YAG:Nd pulsed laser are divided into two special regions, which are the beginning and tail decay regions, corresponding to two time constants, 0.1 ms and 1.0 ms, respectively. Keeping the same light intensity and bias voltage, when the sample was heated to 300°C, the time constants are both reduced. It shows that there are a large number of traps at the position of tens of meV above the valence band edge. The PC ascends S-shaped when the data were collected during the first 200 ns. As the sample is not shined, the PC sharply reduces and oscillates, indicating that the carriers redistributed between the deep traps and the valence band. The experiment results are explained by the model that involves two hole trapping levels, the shallow trapping level and the deep trapping level. Moreover, the mechanism of the curves varied as the light intensities are also explained by the model.

Deep Level Defects in Mg-Doped GaN

Deep level defects in Mg compensated GaN grown by metal-organic vapor phase epitaxy were investigated using photocapacitance spectroscopy measurements on Schottky barrier diodes. Addition of magnesium resulted in the formation of a series of deep centers with optical threshold energies of 1.0, 1.2, 1.8, and 3.1 eV. Upon annealing the epitaxial GCN in nitrogen at 850°C the ind-gap levels disappeared and only the trapping level at 3.1 eV remained. The mid-gap levels are ascribed to Mg dopant complexes which may in part be responsible for low doping efficiency of Mg in the as-grown, doped GaN. The deep level at 3.1 eV commonly observed from all Mgdoped GaN most likely involves the Mg acceptor. The photo-excited state of the 3.1 eV level had relaxation times of the order of 103 sec at 295 K.

A simplified model for thermal discharges

In this study a two-dimensional model has been developed in order to estimate the distribution of temperatures in the marine environment following the discharge of thermal effluents. The model is applicable to any type of marine environment; stratified or uniform. Any density or salinity profile can be handled for the stratified environment. The water column above the diffuser port is divided into a number of layers with thicknesses of 1 or 2 m, depending on the salinity and temperature data and the sea water density is assumed to be uniform within each layer. The average and the minimum dilutions and the average and maximum temperatures are calculated at each layer for the rising plume from port to the trapping level by iterative application of the model equations. This way a diffuser design which satisfies the regulations becomes possible. The model also predicts the dilutions and the temperatures due to subsequent dispersion which occurs during the transport of the field from the seawater surface or from the trapping level depending on the currents and turbulence. The heat transfer between the thermal plume and the ambient seawater is neglected to be on the safe side especially in evaluation of the environmental impact of the thermal discharges. The computer program called THERMOD not only calculates the dilutions and the temperatures, but also draws the contours of equal temperature and temperature differantial (ΔT) lines. The model has been succesfully used in Environmental Impact Assesment Studies of the two 500 MW power plants proposed at the east of Marmara Sea, Turkey.