Showing papers by "Jitendra Kumar published in 1997"

Electron transport and barrier inhomogeneities in palladium silicide Schottky diodes

Abstract: silicon wafer held at 573 K, are measured over a temperature range 37–307 K and analyzed in terms of thermionic emission–diffusion (TED) theory by incorporating the concept of barrier inhomogeneities through a Gaussian distribution function. The process adopted is shown to yield an ideal Schottky diode with a near constant barrier height of 0.734 V and ideality factor 1.05 in the temperature interval 215–307 K. Below 215 K, both the barrier height (φbo) and the ideality factor (η) exhibit abnormal temperature dependence and are explained by invoking two sets of Gaussian distributions of barrier heights at 84–215 K and 37–84 K. Further, it is demonstrated that the forward bias makes the Gaussian distribution dynamic so that the mean fluctuates (i.e., increases or decreases depending on whether its voltage coefficient is positive or negative) and the standard deviation decreases progressively, i.e., the barrier homogenizes temporarily. The changes occur in such a way that the apparent barrier height at any bias is always higher than at zero-bias. Finally, it is pointed out that the presence of single/multiple distributions can be ascertained and the values of respective parameters deduced from the φap vs. 1/T plot itself. Also, the inverse ideality factor versus inverse temperature plot provides bias coefficients of the mean barrier height and standard deviation of the distribution function.

Simulation and analysis of the I-V characteristics of a Schottky diode containing barrier inhomogeneities

Abstract: The current - voltage (I - V) characteristics of Schottky diodes containing barrier inhomogeneities have been simulated using thermionic emission - diffusion (TED) theory and assuming a Gaussian distribution of barrier heights. The system is considered to have a number of non-interacting parallel diodes with each corresponding to a different barrier height within the distribution limit. The mean and the standard deviation of the Gaussian distribution are taken either as constant or having linear bias dependences. The simulated I - V data are then analysed to study the effects of the distribution parameters and their bias coefficients on the barrier height and the ideality factor over a temperature range of 50 - 300 K. It is shown that the mere existence of a distribution causes a decrease in the zero-bias barrier height and, in turn, leads to nonlinearity in the activation energy plots. Also, the decrease is greater for high values of standard deviation. Further, the abnormal increase of ideality factor with decrease in temperature occurs due to the bias dependence of the standard deviation of the distribution. Finally, it is demonstrated that the decrease in temperature and increase in standard deviation cause similar effects and both lead to a decrease in barrier height and an increase in ideality factor. Also, the role of the series resistance in adversely influencing the linearity of the log(I) - V characteristics of a Schottky diode containing barrier inhomogeneities is discussed.

Investigations on the Annealing Effects on Reactively Deposited ITO Thin Films

Abstract: Reactive deposition technique has been adopted to deposit indium tin oxide (ITO) thin films on glass substrates from an In-Sn (90:10 wt%) alloy source. Deposited ITO films were annealed at different temperatures (100 to 325 °C) under nitrogen atmosphere. Structural, optical and electrical properties of the annealed films were investigated. Preferred orientation normal to the (222) plane was observed for the polycrystalline structure of the deposits annealed at various temperatures. Mixed crystallization of In 2 SnO 5 and In 2 Sn 2 O 7-x crystallites was obtained for 150 °C annealing temperature and changed to pure In 2 Sn 2 O 7-x crystallization at higher temperature annealing. A slight increase in the band gap from 3.76 to 3.82 eV was observed when the annealing temperature was raised from 150 to 325 °C. Minimum resistivity of 4.49 x 10 -3 Qcm with maximum carrier concentration 1.94 x 10 20 cm -3 was measured for 150 °C annealed films. Decrease in the carrier concentration and increase in resistivity were observed for the films annealed at higher temperatures. The results are analysed in detail.

Neem Oil Content and its Key Chemical Constituents in Relation to the Agro-ecological Factors and Regions of India

Abstract: The relationship of various agroecological regions and their key factors (ecosystem, growth period, soil type, precipitation) to the yield of neem oil, its key meliacins (azadirachtin-A, nimbin, salannin), and the total as well as the key fatty acids (oleic, stearic, palmitic) is reported. Moderate climate with moderate growth period, the Indo-Gangetic alluvium soil and 400–1600 mm precipitation appeared to be the most conducive for higher oil yield. Oils from the trees grown in desert-saline soil with hot arid climate revealed the highest azadirachtin-A content. The black and Indo-Gangetic alluvium soils with moderate hot semi-arid and hot sub-humid climate with GP 90–180 d were conducive for salannin and nimbin. The coastal ecosystem, coastal alluvium and red soils, GP > 210 d and 2000–3200 mm precipitatton generally favoured oleic, stearic, palmitic and the total fatty acid content of the oils.

Study of residual strains in wafer crystals by means of lattice tilt mapping (

Abstract: A high-resolution X-ray diffractometer equipped with an accurateX-Y translation stage has been used to obtain Bragg angle maps of large-area crystal wafers. It is found that the Bragg angle shifts observed by this method in conventional reflection geometries are mainly due to the local lattice tilts rather than to the lattice parameter changes. The formula to calculate from the lattice tilt maps the displacement of the crystal lattice sites with respect to the ideal unperturbed lattice is obtained. It is shown that such lattice displacement is quantitatively correlated to the wafer dislocation density and to the distribution of the Burgers vectors of the dislocations in the crystal. Semi-insulating Czochraslki-grown GaAs wafers with dislocation densities ranging from 104 to 105cm−2 have been analysed by this technique and by double-crystal X-ray topography. From the lattice tilt maps the dislocation density evaluated appeared similar to those determined by topography and etch pit density in this material. It is concluded that the majority of dislocations in the wafer have the same Burgers-vector component along the (100) growth axis. Finally the method is proposed as a new tool for characterizing large-area wafer crystals.

High Quality GaAs Epitaxial Layers Grown from Ga–As–Bi Solutions by Liquid Phase Epitaxy

Abstract: The liquidus isotherms for the Ga–As–Bi system were determined at 973 and 923 K in the Ga–As–GaAs region. The liquid phase epitaxial growth of GaAs from Ga–As and Ga–As–Bi solutions were investigated. The addition of ten atomic percent of Bi to the Ga–As solution increase the growth rate of the grown epilayers nearly 4.4 times than in the case of GaAs layers from Bi solution. Above 9 at.% of Bi in Ga solution the problems associated with the edge growth were almost eliminated. Optical measurements at 4.2 K revealed that Bi does not alter the band gap energy value of the GaAs epitaxial layers. The photoluminescence (PL) intensity and full width at half maximum (FWHM) revealed the good quality of undoped GaAs epilayers from Bi solvents compared to that of Ga solvents even though the purity of the Bi was relatively less.

Current-voltage characteristics of low energy proton and alpha particle irradiated Au and Schottky barrier diodes

Abstract: Experimental results on the considerable changes in the current-voltage (I–V) characteristics of proton and alpha particle (80 keV) irradiated and Schottky barrier diodes (SBDs) with different fluences are presented. The samples were irradiated at 300 K, after fabricating Au and Ag Schottky barrier diodes on the undoped liquid encapsulated Czochralski (LEC) grown n-GaAs (100) (3 × 1015cm−3). The parameter susceptible to this irradiation is the reverse leakage current of the SBDs. I–V characteristics were measured at different temperatures between 300 and 350 K. A correlation between change in reverse leakage current and incident particle fluence has been observed. The ideality factor and the series resistance of the diode increases with the increase of particle fluence. This may be due to the irradiation-induced defects which reduce the carrier lifetime and/or enhance the interface insulation region.

Liquid Encapsulated Czochralski Growth of Large size Gallium Arsenide and Indium Phosphide Single Crystals and their Characterisation—A Review

Abstract: GaAs and InP single crystals have been grown using Liquid Encapsulated Czochralski (LEC) technique. The grown GaAs ingots are of 2-2.5 inch in diameter and 1–1.5 kg in weight; InP ingots are of 2 i...