Nandita DasGupta

High pressure chemical vapor oxidation of SiC in nitric acid vapor is reported. Higher growth rate at temperatures as low as 400 to 500°C has been achieved. The oxidation kinetics has been studied. It has been observed that the growth rate is strongly dependent on temperature, and the thickness of the oxide increases almost linearly with time within the error limits. X-ray photoelectron spectroscopy (XPS) measurement has been carried out to study the composition of the oxide. Room temperature electrical characterization (current-voltage and capacitance-voltage) has been carried out to estimate the oxide breakdown field strength, oxide charges, and interface state density. It is observed that prolonged oxidation or oxidation at higher temperature in acid ambient deteriorates the quality of oxide. © 2011 The Japan Society of Applied Physics.

Dependence of gate leakage current on Al mole fraction of AlGaN/GaN high-electron mobility transistors (HEMTs) is studied using temperature-dependent current-voltage and capacitance-voltage characteristics. The reverse leakage current is mostly dominated by Poole-Frenkel (PF) emission in the structures used in this brief. However, it is observed that at higher mole fractions, due to higher electric field across the barrier, Fowler-Nordheim (FN) tunneling also contributes to the gate leakage current even at room temperature and above. An expression for critical temperature below which FN tunneling component becomes comparable with or more than PF emission component is presented. It is concluded that the dominant gate leakage mechanisms in III - N HEMTs are dependent on mole fraction of the barrier material and the temperature. However, the relative strengths of PF emission and FN tunneling are also influenced by various process-dependent parameters.

Rapid Thermal Oxidation (RTO) of AlGaN barrier has been employed to reduce the gate leakage current in AlGaN/GaN High Electron Mobility Transistors. Current Voltage (I-V) and Capacitance Voltage (C-V) characteristics of Schottky Barrier diodes and Metal Oxide Semiconductor diodes are compared. At room temperature, reduction in gate leakage current over an order of magnitude in reverse bias and four orders of magnitude in forward bias is achieved upon oxidation. While the gate current reduces upon RTO, gate capacitance does not change indicating gate control over the channel is not compromised. I-V and C-V characterization have been carried out at different temperatures to get more insight into the device operation.

In this paper, we report an accurate quasi-saturation model and a nodal charge model for silicon-on-insulator lateral double-diffused metal-oxide-semiconductor (SOI-LDMOS) transistors. First, a model of a 2-D SOI resistor under velocity saturation is developed, which is subsequently incorporated into the drift region of an LDMOS transistor to predict the quasi-saturation effect. The gate-voltage dependence of the quasi-saturation current is also modeled. Second, we propose a new nodal charge model to describe the dynamic behavior of the device. Comparisons of modeling results with device simulation data show that the proposed model is accurate over a wide range of bias. Scalability of the model with respect to the length of the drift region under the field oxide is also demonstrated. Finally, the model is validated under device self-heating conditions and by comparing it with the experimental data.

Abstract We report on the growth of violet emitting p-type ZnO thin films, with phosphorous (P) and nitrogen (N) codoping, using pulsed laser deposition. XPS studies show that the phosphorous is substituted at Zn site, whereas nitrogen is substituted at oxygen site. Hall measurements confirmed the p-type nature in codoped ZnO thin films. I-V characteristics of the heterojunction formed by n-Si and P, N: ZnO showed rectifying nature. Strong violet emission in PL spectra is attributed to the formation of zinc vacancies. We propose a defect complex, (P Zn -V Zn -4N O ), which acts as an effective acceptor in the P and N codoped ZnO.

In this paper, for the first time, we demonstrate the improvement in power capability and safe operating area of silicon-on-insulator laterally double-diffused MOS (SOI-LDMOS) transistors for power amplifier applications by the introduction of a partial n+ buried layer (PNBL). The power capability of a transistor can be evaluated by Pmax/A, which is the maximum power per unit area that can be delivered by the transistor and is an important parameter for power amplifiers. Pmax is dependent on the snapback voltage (Vsb,QS), OFF-state breakdown voltage (Vbd, OFF), and maximum current (Imax) in the quasi-saturation regime of an LDMOS transistor. Increase of Pmax/A by the introduction of a PNBL in the SOI-LDMOS transistors is reported in this paper. The effects of variation of the length, thickness, and doping concentration of the PNBL on Vsb,QS and Pmax/A are analyzed in detail. It is shown that by optimizing the doping and length of the PNBL layer, the maximum power output from the transistor can be made significantly higher than that of a conventional device without PNBL. A procedure to design the optimized structure is also presented.

We report on the growth of ZnO nanostructures in different gas ambient (Ar and N 2 ) using pulsed laser deposition technique. Despite the similar growth temperature, use of N 2 ambient gas resulted in well-aligned nanorods with flat surface at the tip, whereas, nanorods grown with Ar ambient exhibited tapered tips. The Nanorods grown under N 2 ambient exhibited additional Raman modes corresponding to N induced zinc interstitials. The nanorods are c-axis oriented and highly epitaxial in nature. Photoluminescence spectroscopy reveals that the UV emission can be significantly enhanced by 10 times for the nanorods grown under Ar ambient. The enhanced UV emission is attributed to the reduction in polarization electric field along the c-axis. n-ZnO nanorods/p-Si heterojunction showed rectifying I–V characteristics with a turn of voltage of 3.4 V.

Education theories stress not only societal context of education, but also educational philosophy, anthropology and psychology of learning. A formal curriculum theory, viz. Taba-Tyler rationale, has been proposed to incorporate philosophical, sociological, anthropological and psychological contexts of engineering education in the curriculum. The newly developed undergraduate curriculum at the Indian Institute of Technology Ropar is based on such education theories and has been presented as a case study. It has been demonstrated that the resulting curriculum can lead to unique courses that collectively bring out unique features such as core competency, strong connection to society, hands-on learning, creativity and innovation.

A physics-based compact model for silicon-on-insulator lateral double-diffused metal-oxide-semiconductor transistors including impact ionization, subsequent snapback (SB), and self-heating (SH) is presented. It is observed that the SB effect is caused by the turn-on of the associated parasitic bipolar transistor. The model includes the effect of device SH using resistive thermal networks for each region. Comparisons of modeling results with device simulation data show that, over a wide range of bias voltages, the model exhibits excellent accuracy without any convergence problem. © 2011 IEEE.

An ultrabroadband add-drop filter/switch circuit is designed and demonstrated by integrating a pair of subwavelength grating waveguides in a 2\times 2 Mach-Zehnder interferometer configuration using silicon photonics technology. The subwavelength grating is designed such that its stopband and passband are distinguished by a band-edge wavelength \lambda -{\text{edge}} \sim1565 nm, separating C and L bands. The stopband (\lambda < lambda {\text{edge}}) is filtered at the drop port of the device, whereas the passband ( \lambda >\lambda -{\text{edge}}) is extracted either in cross port or in bar port. The device is designed to operate only in TE polarization. Experimental results exhibit a nearly flat-Top band exceeding 40 nm for both stopband and passband. The stopband extinction at cross-and bar ports are measured to be > 35 dB with a band-edge roll-off exceeding 70 dB/nm. Wavelength independent directional coupler design and integrated optical microheaters at different locations of the Mach-Zehnder arms for thermo-optic phase detuning are the key for stopband filtering at the drop port and switching of passband between cross-and bar ports with flat top response. Though the insertion loss of fabricated subwavelength grating waveguides are negligibly small, the observed passband insertion loss is \sim 2 dB, which is mainly due to the combined excess loss of two directional couplers. Experimental results also reveal that the passband switching between cross-and bar ports of the device has been possible with an extinction of >15 dB by an electrical power consumption of P-\pi \sim 54 mW. A switching time of 5 \mus is estimated by analyzing the transient response of the device. The passband edge could also be detuned thermo-optically at a rate of 22 pm/mW.