Control of barrier height of MIS tunnel diodes using deep level impurities

The barrier height of MIS tunnel diodes is studied considering the effect of deep impurities. It is shown that the barrier height of a given MIS-system can be controlled by changing the density and the activation energy of the defect level. The study leads to the conclusion that deep impurities of character opposite to shallow impurities enhance the barrier height. On the other hand, the barrier height is lowered when the type of the deep impurities is the same as that of shallow impurities.

Excellent rectifying characteristics in Au/n-CdTe diodes upon exposure to rf nitrogen plasma

Nitrogen plasma exposure (NPE) effects on indium doped bulk n-CdTe are reported here. Excellent rectifying characteristics of Au/n-CdTe Schottky diodes, with an increase in the barrier height, and large reverse breakdown voltages are observed after the plasma exposure. Surface damage is found to be absent in the plasma exposed samples. The breakdown mechanism of the heavily doped Schottky diodes is found to shift from the Zener to avalanche after the nitrogen plasma exposure, pointing to a change in the doping close to the surface which was also verified by C-V measurements. The thermal stability of the plasma exposure process is seen up to a temperature of 350 degrees C, thereby enabling the high temperature processing of the samples for device fabrication. The characteristics of the NPE diodes are stable over a year implying excellent diode quality. A plausible model based on Fermi level pinning by acceptor-like states created by plasma exposure is proposed to explain the observations.

A DLTS technique for surface state capture cross-section measurement of MOS diodes

A modified DLTS technique is proposed for the direct measurement of capture cross-section of MOS surface states. The nature of temperature and energy dependence σn is inferred from data analysis. Temperature dependence of σn is shown to be consistent with the observed DLTS line shapes.

Measurement of Turbulence and pitch of the airstream in the 5'* 7' tunnel of Indian Institute of Science

Abstract is not available.

On the ideality factor of Schottky diodes at low temperatures

Abstract is not available.

Growth of tin oxide single crystals in porcelain tunnel kilns

Single crystals of tin oxide have been grown under conditions obtained in oil fired porcelain tunnel kilns. It was noted that the reducing conditions in the kilns help in the growth of SnO2 crystals at much lower temperatures (1300°C). The growth seems to more pronounced in presence of silicon carbide. The crystals grow as long fibres of 0.1 to 0.5 mm dia. and 10 to 50 mm length. The crystals exhibit rutile structure and the direction of growth seems to be favoured in any one of the major axes a and c.

Investigations of separated flow over backward facing steps in IISc hypersonic shock tunnel

Two backward facing step (2 mm and 3 mm step height) models are selected for surface heat transfer measurements. The platinum thin film gauges are deposited on the Macor inserts using both hand paint and vacuum sputtering technique. Using the Eckert reference temperature method the heating rates has been theoretically calculated along the flat plate portion of the model and the theoretical estimates are compared with experimentally determined surface heat transfer rate. Theoretical analysis of heat flux distribution down stream of the backward facing step model has been carried out using Gai’s non-dimensional analysis. Based on the measured surface heating rates on the backward facing step, the reattachment distance is estimated for 2 and 3 mm step height at nominal Mach number of 7.6. It has been found from the present study that for 2 and 3 mm step height, it approximately takes about 10 and 8 step heights downstream of the model respectively for the flow to re-attach.

Measurement of aerodynamic forces for missile shaped body in hypersonic shock tunnel using 6-component accelerometer based balance system

This paper reports the basic design of a new six component force balance system using miniature piezoelectric accelerometers to measure all aerodynamic forces and moments for a test model in hypersonic shock tunnel (HST2). Since the flow duration in a hypersonic shock tunnel is of the order of $1$ ms, the balance system [1] uses fast response accelerometers (PCB Piezotronics; frequency range of 1-10 kHz) for obtaining the aerodynamic data. The alance system has been used to measure the basic aerodynamic forces and moments on a missile shaped body at Mach $8$ in the IISc hypersonic shock tunnel. The experimentally measured values match well with theoretical predictions.

Shock tunnel testing of a Mach 6 hypersonic waverider

A waverider is a lifting body configuration whose upper surface is parallel to the free stream, and the lower surface aerodynamically so designed, that the resulting shock at the design Mach number, is always attached with the leading edge of the vehicle. This prevents spillage from high pressure (lower) surface to the low pressure (upper) surface.In the present study a conical waverider has been designed, fabricated and tested at Mach 6 in the IISc hypersonic shock tunnel HST2. The measurements show that the waverider has a lift to drag ratio of 4.28 at the designed Mach number. Exhaustive FEM and CFD studies are also carried out to complement the force measurements in the tunnel.

The role of triplet states in the emission mechanism of polymer light-emitting diodes

The blue emission of polyfluorene (PF)-based light-emitting diodes (LEDs) is known to degrade due to a low-energy green emission, which hitherto has been attributed to oxidative defects. By studying the electroluminescence (EL) from ethyl-hexyl substituted PF LEDs in the presence of oxygen and in an inert atmosphere, and by using trace quantities of paramagnetic impurities (PM) in the polymer, we show that the triplet states play a major role in the low-energy emission mechanism. Our time-dependent many-body studies show a large cross-section for the triplet formation in the EL process in the presence of PM, primarily due to electron-hole recombination processes.

Drive current boosting of n-type tunnel FET with strained SiGe layer at source

Though silicon tunnel field effect transistor (TFET) has attracted attention for sub-60 mV/decade subthreshold swing and very small OFF current (IOFF), its practical application is questionable due to low ON current (ION) and complicated fabrication process steps. In this paper, a new n-type classical-MOSFET-alike tunnel FET architecture is proposed, which offers sub-60 mV/decade subthreshold swing along with a significant improvement in ION. The enhancement in ION is achieved by introducing a thin strained SiGe layer on top of the silicon source. Through 2D simulations it is observed that the device is nearly free from short channel effect (SCE) and its immunity towards drain induced barrier lowering (DIBL) increases with increasing germanium mole fraction. It is also found that the body bias does not change the drive current but after body current gets affected. An ION of View the MathML source and a minimum average subthreshold swing of 13 mV/decade is achieved for 100 nm channel length device with 1.2 V supply voltage and 0.7 Ge mole fraction, while maintaining the IOFF in fA range.

Investigations on magnetron sputtered ZnO thin films and Au/ZnO Schottky diodes

Magnetron sputtering is a promising technique for the growth of oxide materials including ZnO, which allows deposition of films at low temperatures with good electrical properties. The current-voltage (I-P) characteristics of An Schottky contacts on magnetron sputtered ZnO, films have been measured over a temperature range of 278-358K. Both effective barrier height (phi(B,eff)) and ideality factor (n) are found to be a function of temperature, and this behavior has been interpreted on the basis of a Gaussian distribution of barrier heights due to barrier height inhomogeneities that prevail at the interface. Density of states (DOS) near the Fermi level is determined using a model based on the space charge limited current (SCLC). The dispersion in both real and imaginary parts of the dielectric constant at low frequencies, with increase in temperature is attributed to the space charge effect. Complex impedance plots exhibited two semicircles, which corresponds to bulk grains and the grain boundaries. (c) 2006 Elsevier B.V. All rights reserved.

Simultaneous measurement of aerodynamic and heat transfer data for large angle blunt cones in hypersonic shock tunnel

Aerodynamic forces and fore-body convective surface heat transfer rates over a 60 degrees apex-angle blunt cone have been simultaneously measured at a nominal Mach number of 5.75 in the hypersonic shock tunnel HST2. An aluminum model incorporating a three-component accelerometer-based balance system for measuring the aerodynamic forces and an array of platinum thin-film gauges deposited on thermally insulating backing material flush mounted on the model surface is used for convective surface heat transfer measurement in the investigations. The measured value of the drag coefficient varies by about +/-6% from the theoretically estimated value based on the modified Newtonian theory, while the axi-symmetric Navier-Stokes computations overpredict the drag coefficient by about 9%. The normalized values of measured heat transfer rates at 0 degrees angle of attack are about 11% higher than the theoretically estimated values. The aerodynamic and the heat transfer data presented here are very valuable for the validation of CFD codes used for the numerical computation of How fields around hypersonic vehicles.