Mahaveer Kumar Jain

Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10-6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films.

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.

We describe the effect of annealing in air and in vacuum on structural, electrical and optical properties of indium nitride (InN) thin films. The films were grown by modified activated reactive evaporation. Films annealed in air were transformed to In2O3 at 450 °C whereas films annealed in vacuum started decomposing at 500 °C. The c-lattice constant was found decreasing for increasing annealing temperature due to reduction of excess nitrogen in the films. The major changes in structural, electrical and optical properties appear around 400 °C. Both air and vacuum-annealed films show a reduction in the carrier concentration with annealing, explaining the observed reduction in bandgap (Moss-Burstein shift) for vacuum-annealed films. For air-annealed films, the bandgap increases when annealed, which may be due to oxynitride formation overcoming the effect of reduced carrier concentration. A decrease in the photoluminescence intensity was observed at 400 °C for air-annealed and 500 °C for vacuum-annealed films which can be attributed, respectively, to the presence of indium oxide and indium in the films. Optimal annealing temperature was observed between 400 and 450 °C in vacuum. © 2009 Elsevier B.V. All rights reserved.

We report the effect of rf power on the structural, optical and electrical properties of InN films grown by modified activated reactive evaporation. In this technique, the substrates were kept on the cathode instead of ground electrode. The films grown at higher rf power shows preferential c-axis orientations for both silicon and glass substrates. The films prepared at 100 W show best structural, electrical and optical properties. The c-axis lattice constant was found to decrease with increase in rf power which can be attributed to reduction in excess nitrogen in the films. The band gap decreases with increase in rf power due to Moss-Burstein shift. The decrease in carrier concentration and optical band gap with increase in rf power can also be related to excess nitrogen in the film. The Raman spectra shows a red shift in the A 1 (LO) and E 2 (high) mode from the reported value. The possible origin of the present large band gap is due to Moss-Burstein shift. The new film growth method opens opportunities for integrating novel substrate materials with group III nitride technologies. © 2008 Elsevier B.V. All rights reserved.

Indium-rich InxGa1-xN thin films were prepared on glass substrates by a mixed source modified activated reactive evaporation technique. All the films exhibit hexagonal wurtzite structure preferentially oriented along the c-axis. The band gap values obtained through Urbach fitting of the absorption edge were found to be in good agreement with the values obtained from photoluminescence spectra. The decrease in band gap below 1.9 eV (i.e., for pure InN) for indium-rich films is mainly due to the compensation of BursteinMoss shift due to gallium incorporation into the lattice which is further confirmed from the carrier concentration measurements. © 2011 World Scientific Publishing Company.

Monolithic microwave integrated circuits (MMICs) play an important part in today's wireless communication electronics. GaAs-based pseudomorphic High Electron Mobility Transistor (pHEMT) is used in MMIC-based low noise amplifier (LNA) and power amplifier (PA) stages. The latter requires high device current (Ids) and high reverse breakdown voltage (BVgd). In addition, the ON-state breakdown voltage should be high enough to operate the device at higher source-drain voltage (Vds). Double gate recessing is a well-established technique used to increase the ON and OFF-state breakdown voltages of a pHEMT device for power applications, which requires two levels of masking and recessing. In this paper, we present a single mask processing technique for realizing double recess structure with the help of silicon nitride layer. The new process involves deposition of silicon nitride after mesa isolation step of device fabrication. After gate lithography, two etching steps of silicon nitride and GaAs, followed one after the other, generates the double recess structure, wherein the various etch times decide the width and shape of double recess structure. The electric field distribution at the Schottky interface as well as along the channel has been simulated using ATLAS for the double recess structure used in this work. The fabricated recess structure showed improvement in breakdown voltage of the device which has been correlated to the effective redistribution of electric field in the device, as shown by simulation. © 2014 Elsevier B.V. All rights reserved.

Indium nitride films have been grown using modified activated reactive evaporation (MARE). The films were grown on glass and silicon substrates at room temperatures, i.e. without any intentional substrate heating. In this technique, the substrates were kept on the cathode instead of the grounded electrode and hence subjected to low energy nitrogen ion bombardment leading to highly c-axis oriented films. The photoluminescence (PL) and Raman spectrum shows significant improvement in the quality of the films compared with conventional activated reactive evaporation. The band gap measured from the room temperature PL was found to be 1.9 eV. Very high growth rates can be achieved in the MARE growth technique. The modification in the activated reactive evaporation technique may have a large impact on the growth of various compounds such as metal oxides. © 2008 IOP Publishing Ltd.

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.

We report the fabrication of pseudomorphic high electron mobility transistors (pHEMTs) with engineered recess structure of any width of choice, by a single lithography and etching step with the help of silicon-nitride-assisted process. In this process, a silicon nitride layer is deposited prior to gate lithography. First, the silicon nitride is etched by buffered hydrofluoric acid (BHF) in the gate opening and then selective recessing is performed. The recess base width can be engineered by varying etch time of silicon nitride in BHF. The base width increases linearly with etch time as shown by SEM. We demonstrate that the top photoresist gate opening that decides the gate length is unaffected by any duration of silicon nitride etch time. Thereby, we have engineered the distance from gate edge to n +-GaAs (L gn+) which decides the gate-to-drain breakdown voltage (BV gd). With this method, BV gdincreased from 12 to 20V as a function of L gn+. The electric field distribution across the recess structure has been simulated to interpret this result. Since the high BV gdof pHEMT is essential for power applications as well as switch applications, this method can be easily adopted even though the corresponding reduction in transconductance and unit current gain cut-off frequency (f t) is only marginal from 375 to 350 mS mm 1and from 39 to 31GHz, respectively. © 2012 IOP Publishing Ltd.

InN films are grown on silicon and glass substrates by radio frequency (rf) activated reactive evaporation. High purity indium (99.99) is evaporated by resistive heating in the presence of nitrogen plasma. X-ray diffraction shows that the film deposited at low rf plasma powers (≤100 W) are indium rich and further increase in the rf power formation of InN take place. The average crystallite size was found varying from 8 nm to 20 nm as the power increases from 200 to 400 W. The diffraction pattern shows the polycrystalline nature of InN films. The band gap obtained from the transmission spectra show an increase in the band gap with the increase in rf power which can be attributed to variation of nitrogen: indium stoichiometry. The Raman spectra shows wurtzite nature of the film and the photoluminescence measurements show a weak peak around 1.81 eV for the film grown at 400 W. Plasma diagnostics has been carried out in order to understand the role of active species in the process. The large shift in the band gap is attributed to Moss-Burstein shift and presence of residual oxygen in the film. © 2009 American Scientific Publishers All rights reserved.