Performance analysis of a bipolar mode FET (BMFET) with normallyoff characteristics

The fabrication and characterization of a family of power bipolar-mode junction FETs (BMFETs) are reported. Blocking voltages up to 1000 V or currents up to 18 A (corresponding to 800 A/cm²) have been obtained. The experimental results are used to get an insight into the physics of BMFET operation and to extract the basic design criteria for these structures. The performance of the BMFET is compared with that of the bipolar transistor, showing it to be superior     

A quasi-one-dimensional analysis of vertical JFET devices operated in the bipolar mode

“Bipolar operation”, namely forward-basing the gate-source diode of a JFET, has been proposed in the literature as a means to reduce the on-state resistance of such devices.In this paper, the physics of bipolar operation of power JFET's is analysed in detail and closed-form solutions of its output characteristics are derived as a function of the device geometry and of physical parameters of the semiconductor.From that model, it turns out that the low value of the saturation voltage originates from the existence of an high-density electron-hole plasma that fills the space between source and drain. In the active region of the output characteristics, the control of the gate current the drain current is due to the possibility to control the level of majority-carrier injection from the source transition. The closed-form expression for the current gain allows to identify the structure parameters that affect it. It shown that, under suitable conditions, a substantial current amplification can be observed.The model has been found to be in good agreement with the results obtained on experimental devices.     

Revealing Photoluminescence Modulation from Layered Halide Perovskite Microcrystals upon Cyclic Compression

Halide perovskites show promise for high‐efficiency solar energy conversion and light‐emitting diode devices owing to their bandgap, which falls within the visible optical range. However, due to their rigidity, GPa pressures are necessary to control the complex interplay between their electronic and crystallographic structure. Layered perovskites are likely to be controlled using much lower pressures by exploiting the optical anisotropy of the embedded organic molecules in the structure. This work introduces layered perovskite microplatelets and demonstrates the extreme sensitivity of their emission to cyclic mechanical loading in the range of tens of MPa. A drastic change in their emission is observed in situ, from near‐white to an enhanced blue color. This process is reversible, as is evident from a hysteresis loop in the photoluminescence (PL) intensity of the microplatelets. A combination of experimental analysis and computational modelling shows that such behavior cannot be attributed to changes in the crystallographic structure of the flakes. Instead, it suggests that, thanks to their structural anisotropy, microplate alignment and reorientation are responsible for the observed PL modulation. The possibility to tune the optical emission of layered perovskite crystals via low pressures makes them highly interesting as active materials in applications where stress sensing or light modulation is desired.     

Numerical analysis of local lifetime control for high-speedlow-loss P-i-N diode design

The effect of localized lifetime control technique on the static and dynamic behavior of a power P-i-N diode is investigated in this paper. Mixed mode device circuit simulations are used in order to analyze the effect of the width and position of a reduced lifetime region on the diode. The simulations show that the optimal position for the low-lifetime region is at the beginning of the base region on the anode side, while the optimal width of the low-lifetime region depends on the amount of lifetime reduction. The local lifetime control design technique is shown to be effective in reducing the turn-off time and increasing diode softness with a little worsening of on-state voltage drop. It is shown that the tradeoff curve obtained by diodes using local lifetime control is better than the one achieved with lifetime killing in the whole epilayer region     

Characterization of recombination centers in Si epilayers after He implantation by direct measurement of local lifetime distribution with the AC lifetime profiling technique

The distribution of recombination centers induced in Si epi-substrates by helium (He) implantation is obtained for the first time by direct measurement of local recombination lifetime profile along the layer, using the ac differential lifetime profiling technique. The different energy levels of the recombination centers induced by He implantation at different doses and energies have been extracted, as a function of the position in the layer, by temperature scanning of the lifetime profiles. The lifetime measurements clearly demonstrate the presence of a secondary defect distribution that extend from the region of maximum primary damage both at lower and higher depths respect to the stopping range depth, due to the relatively large concentration of primary defects created near the stopping range, and give a coherent picture of the effects of He implant on the "local" lifetime.     

Longitudinal trajectories and predictors of adolescent suicidal ideation and attempts following inpatient hospitalization.

Remarkably little is known regarding the temporal course of adolescent suicidal ideation and behavior, the prediction of suicidal attempts from changes in suicidal ideation, or the prediction of suicidal attempts after accounting for suicidal ideation as a predictor. A sample of 143 adolescents 12-15 years old was assessed during psychiatric inpatient hospitalization and again at 3, 6, 9, 15, and 18 months postdischarge through a series of structured interviews and parent- and adolescent-reported instruments. Symptoms of depression, posttraumatic stress disorder, externalizing psychopathology, hopelessness, and engagement in several forms of self-injurious/suicidal behaviors (i.e., suicide threats/gestures, plans, nonsuicidal self-injury [NSSI]) were assessed. Latent growth curve analyses revealed a period of suicidal ideation remission between baseline and 6 months following discharge, as well as a subtle period of suicidal ideation reemergence between 9 and 18 months postdischarge. Changes in suicidal ideation predicted suicide attempts. After accounting for the effects of suicidal ideation, baseline suicide threats/gestures also predicted future suicide attempts. Higher adolescent-reported depressive symptoms, lower parent-reported externalizing symptoms, and higher frequencies of NSSI predicted weaker suicidal ideation remission slopes. Findings underscore the need for more longitudinal research on the course of adolescent suicidality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A novel UIS test system with Crowbar feedback for reduced failure energy in power devices testing

A new unclamped inductive load (UIS) test system is presented, provided with a Crowbar protection that is able to “sense” the failure of the DUT. Differently from the standard UIS test systems with a Crowbar device, this system turns on the Crowbar only when it is really needed i.e. immediately after the DUT fails during the breakdown transient. This was achieved by feeding back the DUT collector voltage to the test system control electronics. Our measurements performed on commercial power devices show that this improved UIS test system can, in the event of a failure, drastically reduce the energy dissipated on the DUT and hence its related damage effects, giving the possibility of locating the failure starting point with better accuracy and performing subsequent analyses on the damaged devices aimed to infer the failure causes.     

Controlling DNA Bundle Size and Spatial Arrangement in Self-assembled Arrays on Superhydrophobic Surface

Nano-Micro Letters - The use of superhydrophobic surfaces (SHSs) is now emerging as an attractive platform for the realization of one-dimensional (1D) nanostructures with potential applications in...     

An equivalent time temperature mapping system with a 320 x 256 pixels full-frame 100 kHz sampling rate

In this paper we describe a novel temperature mapping system based on a standard infrared camera with 50 Hz frame rate for the measurement of ultrafast temperature transients which, in principle, demand for a much faster acquisition rate. In particular, we base our system on the widely used equivalent time sampling concept which can be adapted to the temperature acquisition system, thanks to a very fast and sensitive camera sensor: an InSb sensor, which allows a reduced integration time of 10 micros, and a custom digital synchronization circuit. The latter has been realized by the usage of a fully programmable digital circuit, which generates all the signals needed for the synchronization of the IR camera, of the experiment, and a personal computer needed for data acquisition and storage. We show, with experiments, how this system is capable of detecting temperature transients with an equivalent bandwidth of 100 kHz full frame, far beyond the capabilities of the fastest available IR cameras.