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.

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.

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.

Nitrogen doped ZnO (NZO) thin films, at different +{\hbox{N}} 2 flow rates have been deposited on glass substrates by pulsed DC reactive magnetron sputtering technique. The effect of +{\hbox{N}} 2 flow rate (1.0 sccm - 3.0 sccm) on the structural, optical, electrical and chemical state of N has been studied. With the effect of +{\hbox{N}} 2 flow rate: the crystallinity of the films decreased, tensile stress is developed, optical transmittance decreased (80% to 60%), conductivity decreased till 1.5 sccm and films were n-type conducting. At 2.0 sccm and 2.5 sccm of +{\hbox{N}} 2 flow rates, NZO thin films showed p-type conductivity. The changes in the magnitude and type of conductivity have a direct relation with the changes observed in N-chemical state in ZnO lattice. p- NZO thin films are electrically unstable; this instability has been explained based on the changes occurred in the N chemical states, resulting from the stress release in NZO lattice. © 2005-2012 IEEE.

We report the preparation of polycrystalline GaN films on glass substrates by modified activated reactive evaporation (MARE). In this technique, substrates are kept on cathode instead of ground electrode and hence subjected to low-energy nitrogen ion bombardment. With increase in rf power, nitrogen to gallium (N/Ga) ratio in the films and film resistivity monotonically increases whereas oxygen impurity reduces. All GaN films are of wurtzite structure and films grown at higher powers have preferred orientation towards c-axis. Crystalline quality improves with increase in rf power up to ∼150 W and thereafter it degrades. Improvement in crystalline quality can be attributed to Ga/N stoichiometry and reduction in oxygen concentration, whereas degradation can be attributed to the presence of point defects due to excess nitrogen and nitrogen ion bombardment. Optical emission spectroscopy (OES) is used to investigate the relative concentration of excited species during GaN growth. MARE offers a technique to grow low-temperature group III nitride semiconductors. A high deposition rate (4.3 μm/h) was achieved in MARE for growing polycrystalline films on relatively inexpensive substrates. MARE is relatively less complex and offers a viable alternative for large scale growth for polycrystalline GaN thin films. © 2009.

In this report, we have studied the compositional dependence of structural, optical and electrical properties of polycrystalline In x Ga 1-x N thin films grown by modified activated reactive evaporation. The growth was monitored by optical emission spectroscopy. The thickness of the films was in the range ∼600-800 nm. The phase, crystallinity and composition of the films were determined by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analysis. The surface morphology was studied by atomic force microscopy. The band gaps of these films obtained from transmittance and photoluminescence measurements were found to vary from 1.88 to 3.22 eV. All the films show n-type conductivity. The carrier concentration was found to be decreasing with increase in gallium incorporation which is in good agreement with the free carrier absorption observed in transmittance spectra. © 2012 Springer Science+Business Media, LLC.

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.