Showing papers by "Jitendra Kumar published in 2002"

Thermal stability of GaN epitaxial layer and GaN/sapphire interface

Abstract: Thermal stabilities of GaN epitaxial layer and of GaN/sapphire interface has been investigated using Raman scattering, photoluminescence (PL), optical transmission and SEM analysis. GaN epitaxial layers were annealed up to temperatures as high as 1100°C in nitrogen ambient for a period of 20 min. Raman scattering identifies two new additional vibrational modes in GaN between E2 and Al(LO) modes for the samples annealed beyond 900°C. Annealing up to the temperature of 900°C enhances the PL intensity and it is decreased drastically for the high-temperature annealed samples. Optical transmission and SEM studies exhibit a clear indication of reaction between GaN/sapphire interface at higher temperatures above 1000°C.

Studies on the proton irradiation induced defects on Ni/n-GaAs Schottky barrier diodes

Abstract: Ni/n-GaAs Schottky barrier diodes (SBDs) have been irradiated using low energy proton ions of fluences 1×10 14 , 1×10 15 and 1×10 16 cm −2 to study the effect of irradiation damages very close to the interface. Current–voltage ( I – V ) and capacitance–voltage ( C – V ) characteristics of control and irradiated diodes have been carried out. The change in the reverse leakage current increases with increasing ion fluences. The barrier height of the SBDs has been found to decrease and the ideality factor deviates from the ideal behavior with increasing ion fluences. This non-rectifying behavior is due to the irradiation induced defects at the interface. The rectifying behavior of the SBDs improved, upon annealing at 573 and 673 K. The capacitance value of the irradiated diodes has been found to be less than the control diodes and it increases with increasing ion fluences. The capacitance of the irradiated and annealed diode decreases for all fluences due to the removal of the irradiation induced defects in the depletion region. The carrier concentration reduces by the proton irradiation through the mechanism of passivation and defects trapping at the interface and within in the depletion region. The time resolved luminescence spectrum in proton irradiated GaAs has been carried out in order to measure the life times of the photo excited carriers as a function of fluence. It is observed the carrier lifetimes decrease with increasing fluences.

Morphological, Chemical and Genetic Variability in Neem Accessions

Abstract: Fifty-eight accessions of neem collected from two agro-ecological regions of North-western plains of India covering the states of Punjab, Haryana and Rajasthan were characterized at morphological, chemical and molecular level to ascertain the variability. For statistical treatment, the regions were sub-divided into sub-zones (categories) with the sub-zone 5 further sub-divided into two. Seed characters for morphological, oil, azadirachtin, salannin and nimbin for chemical and six AFLP primer combinations for molecular evaluation were considered. Variability was observed for all the morphological and chemical characters amongst the samples. Among the categories, significant chemical variability existed for azadirachtin-A but the morphological variability was non-significant. At molecular level the genetic similarity (Jaccard's coefficient) varied from 0.07 to 0.759. UPGMA cluster analysis grouped the accessions into five, four and three clusters, respectively based on genetic, morphological and chemical analyses. The dendrograms based on these three parameters revealed no uniformity in their grouping pattern. A high correlation between the cophenetic and dissimilarity matrices has been observed, the correlation being the highest for genetic (r = 0.969) followed by morphological (r = 0.835) and chemical (r = 0.727) matrices. Mantel's test revealed a low correlation among the three parameters.

PREPARATION AND CHARACTERISATION OF Ti/BaTiO3/InP MIS STRUCTURES

Abstract: Indium Phosphide (InP) is one of the most promising materials for high-speed electronic and optoelectronic devices. In the present investigation n-type InP substrates of orientation grown by LEC technique in our laboratory were used to study the surface state densities. The wafer was polished with HBr:K2Cr2O7:H2O (BCA) polishing solution and decreased with organic solvents. Au:Ge was used has a back ohmic contact and the wafer was annealed at 623K for 5 min. under nitrogen ambient. Barium Titanante (BaTiO3), a dielectric material was used as an insulator to fabricate InP-MIS structures. BaTiO3 thin film has been deposited on InP substrates by sol-gel technique through organic precursor route. Titanium metal contact was made on the BaTiO3 to obtain MIS structure. Compositional analysis of the BaTiO3 thin film on InP substrates has been carried out using XPS and EDX. By the Capacitance Voltage measurements a minimum surface state density (Nss) value as low as 4.5 × 1010cm-2eV-1 has been obtained for T...