Mahaveer Kumar Jain

Metamorphic HEMTs on GaAs substrates are promising devices of today as they are operated at even higher frequencies for microwave applications compared to pseudomorphic HEMTs. The selective removal of n+ InGaAs ohmic contact layer from the top of the device structure poses a major challenge during fabrication. We have studied the influence of temperature on the selectivity of etch rate between the n+ InGaAs and underlying InAlAs layers using Succinic acid based etchant. The etchant was composed of Succinic acid solution mixed with hydrogen peroxide and deionised water. The pH of the solution was adjusted to 5 by adding NH4OH. The etch rates at different temperatures between 14°C to 30°C were estimated by profiling the etched pattern using Atomic Force Microscopy (AFM). Surface roughness of the etched area also was studied using AFM. It was found that the selectivity has improved with temperature. This is possibly due to simultaneous occurrence of low etch rates of InAlAs due to presence of aluminum oxide and high etch rates of InGaAs due to increased temperature. It was also found that the surface roughness was higher at lower temperatures contrary to the observations made in the case of pseudomorphic HEMTs. © 2007 IEEE.

Copper nitride thin films have been prepared by pulsed direct current reactive magnetron sputtering. Structural, morphological and optical properties of the as-deposited films have been studied. X-ray diffraction analysis shows that the films are polycrystalline single phase of Cu3N. Prominent growth along (100) plane is observed for higher nitrogen flow rate whereas growth along (111) plane is observed for relatively lower nitrogen flow rate. The band gap of this material changes from 1.02 to 1.40 eV by varying the nitrogen flow rate and deposition time. © 2013 IEEE.

Zn 1-x Cd x O thin films have been prepared by sol-gel spin coating method. Structural analysis shows that the Cd substitution into the wutrzite ZnO lattice is achieved up to about 20 mol %. The optical band gap is found to decrease with the increase in Cd content. Increase in the annealing temperature up to a certain critical temperature leads to band gap narrowing because of the proper substitution of Zn by Cd and thereafter the band gap increases due to Cd re-evaporation from the lattice sites. This critical temperature lowers down with the increase in Cd doping concentration. The resistivity decreases with the increase in Cd content and increases with the increase in annealing temperature.

Nano-crystalline c-axis orientated indium nitride (InN) thin films were prepared on amorphous polycarbonate, polyimide and glass substrates by modified activated reactive evaporation (MARE) method without any intentional heating of the substrate. The films show strong visible photoluminescence (PL) peak at ~ 1.95 eV indicating the band edge transition which is in good agreement with the optical absorption. The shift in the band gap from reported value is mainly due to Burstein-Moss shift and presence of residual oxygen. InN film grown on inexpensive flexible substrates at room temperature opens opportunity for large scale device applications like solar cells and displays. © 2009 American Institute of Physics.

In this paper we report for the first time, a method of generating wide gate recess structure in single recess step by the help of a bi-layer lithography technique, which can be used to generate varying gate recess width by varying developmental time. It is established that the gate recess structure decides the schottky breakdown voltages in these devices. The distance from gate edge-to-n+ in the recess structure becomes very critical for high Vb. Commonly, double recessing is used to achieve this, which is more complicated. We have achieved Vb as high as 20Volts using single recess. ©2009 IEEE.

Phase homogeneity and crystal structure of melt-quenched AgInSbTe system have been analyzed using X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinement of crystal structure of Ag4In12Sb 56Te28 has revealed the formation of AgIn 3Te5, Sb8Te3 and Sb phases respectively with P-type tetragonal (P42c), 11R (R3m) and A7 (R3m) structures. Addition of suitable amount of Te to Ag4In12Sb 56Te28 yielded Ag3.54In10.62Sb 49.56Te36.28, alloy with AgIn3Te5 and Sb8Te3 phases. Optical micrographs of surface of the samples have shown the existence of three kinds of regions (AgIn 3Te5 rich, Sb8Te3 rich and Sb rich regions) with different reflectivity. Presence of multiphase and effect of laser-sample interaction at these regions have been investigated using Raman spectroscopy. Analysis of Raman spectra has revealed that the regions with more content of AgIn3Te5 exhibit amorphous phase during laser-sample interaction. © 2013 American Institute of Physics.