Electroluminescence from GaN-polymer heterojunction

Inorganic and organic semiconductor devices are generally viewed as distinct and separate technologies. Herein we report a hybrid inorganic-organic light-emitting device employing the use of an air stable polymer, Poly (9,9-dioctylfluorene-alt-benzothiadiazole) as a p-type layer to create a heterojunction, avoiding the use of p-type GaN, which is difficult to grow, being prone to the complex and expensive fabrication techniques that characterises it. I-V characteristics of the GaN-polymer heterojunction fabricated by us exhibits excellent rectification. The luminescence onset voltage is typically about 8-10 V. The device emits yellowish white electroluminescence with CIE coordinates (0.42, 0.44). (C) 2011 Elsevier B.V. All rights reserved.

Performance Enhancement of the Tunnel Field Effect Transistor using SiGe Source

Due to extremely low off state current (IOFF) and excellent sub-threshold characteristics, the tunnel field effect transistor (TFET) has attracted a lot of attention for low standby power applications. In this work, we aim to increase the on state current (ION) of the device. A novel device architecture with a SiGe source is proposed. The proposed structure shows an order of improvement in ION compared to the conventional Si structure. A process flow adaptable to conventional CMOS technology is also addressed.

A Simulation Based Study and Analysis of Double Gate Tunnel FET Performance for Low Stand-By Power Applications

The conventional metal oxide semiconductor field effect transistor (MOSFET)may not be suitable for future low standby power (LSTP) applications due to its high off-state current as the sub-threshold swing is theoretically limited to 60mV/decade. Tunnel field effect transistor (TFET) based on gate controlled band to band tunneling has attracted attention for such applications due to its extremely small sub-threshold swing (much less than 60mV/decade). This paper takes a simulation approach to gain some insight into its electrostatics and the carrier transport mechanism. Using 2D device simulations, a thorough study and analysis of the electrical parameters of the planar double gate TFET is performed. Due to excellent sub-threshold characteristics and a reverse biased structure, it offers orders of magnitude less leakage current compared to the conventional MOSFET. In this work, it is shown that the device can be scaled down to channel lengths as small as 30 nm without affecting its performance. Also, it is observed that the bulk region of the device plays a major role in determining the sub-threshold characteristics of the device and considerable improvement in performance (in terms of ION/IOFF ratio) can be achieved if the thickness of the device is reduced. An ION/IOFF ratio of 2x1012 and a minimum point sub-threshold swing of 22mV/decade is obtained.

Advances in Light-Emitting Doped Semiconductor Nanocrystals

Insertion of just a few impurity atoms in a host semiconductor nanocrystal can drastically alter its phase, shape, and physical properties. Such doped nanomaterials now constitute an important class of optical materials that can provide efficient, stable, and tunable dopant emission in visible and NIR spectral windows. Selecting proper dopants and inserting them in appropriate hosts can generate many new series of such doped nanocrystals with several unique and attractive properties in order to meet current challenges in the versatile field of luminescent materials. However, the synthesis of such doped nanomaterials with a specific dopant in a predetermined host at a desired site leading to targeted optical properties requires fundamental understanding of both the doping process as well as the resulting photophysical properties. Summarizing up to date literature reports, in this Perspective we discuss important advances in synthesis methods and in-depth understanding of the optical properties, with an emphasis on the most widely investigated Mn-doped semiconductor nanocrystals.

Investigations on multimagnetron sputtered Zn1-xMgxO thin films through metal-ferroelectric-semiconductor configuration

The effect of Mg doping in ZnO is investigated through structural, electrical, and optical properties. Zn1−xMgxO (0<×<0.3) thin films were deposited on Si (100) and corning glass substrates using multimagnetron sputtering. Investigations on the structural properties of the films revealed that the increase in Mg concentration resulted in phase evolution from hexagonal to cubic phase. The temperature dependent study of dielectric constant at different frequencies exhibited a dielectric anomaly at 110 °C. The Zn0.7Mg0.3O thin films exhibited a well-defined polarization hysteresis loop with a remnant polarization of 0.2 μC/cm2 and coercive field of 8 kV/cm at room temperature. An increase in the band gap with an increase in Mg content was observed in the range of 3.3–3.8 eV for x = 0–0.3. The average transmittance of the films was higher than 90% in the wavelength region λ = 400–900 nm.

A Fluidic Drive System for Intra-Aortic Balloon Heart Assist Device

Intra-aortic balloon pumping is a counter pulsation technique for temporary circulatory assistance in cardiogenic shock and other low cardiac output conditions. Conventional systems use a balloon at the end of a catheter driven by a solenoid valve, controlled by patient's ECG or ventricular pressure signal. This results in time delay introducted by solenoid spool inertia, gas inertia, and hysteresis effects of the solenoid. Fluidics, because of their non-moving part operation and high switching speeds, minimizes the inertial effects while contributing high reliability. This communication describes a fluidic system developed for driving the balloon accepting electric control signals.

Digital Dead Time Logic and Protection Circuitry for PWM Voltage Source Converters

Power semiconductor devices have finite turn on and turn off delays that may not be perfectly matched. In a leg of a voltage source converter, the simultaneous turn on of one device and the turn off of the complementary device will cause a DC bus shoot through, if the turn off delay is larger than the turn on delay time. To avoid this situation it is common practice to blank the two complementary devices in a leg for a small duration of time while switching, which is called dead time. This paper proposes a logic circuit for digital implementation required to control the complementary devices of a leg independently and at the same time preventing cross conduction of devices in a leg, and while providing accurate and stable dead time. This implementation is based on the concept of finite state machines. This circuit can also block improper PWM pulses to semiconductor switches and filters small pulses notches below a threshold time width as the narrow pulses do not provide any significant contribution to average pole voltage, but leads to increased switching loss. This proposed dead time logic has been implemented in a CPLD and is implemented in a protection and delay card for 3- power converters.