Acetylene-Based Materials in Organic Photovoltaics

Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Organic photovoltaic systems hold the promise of a lightweight, flexible, cost-effective solar energy conversion platform, which could benefit from simple solution-processing of the active layer. The discovery of semiconductive polyacetylene by Heeger et al. in the late 1970s was a milestone towards the use of organic materials in electronics; the development of efficient protocols for the palladium catalyzed alkynylation reactions and the new conception of steric and conformational advantages of acetylenes have been recently focused the attention on conjugated triple-bond containing systems as a promising class of semiconductors for OPVs applications. We review here the most important and representative (poly)arylacetylenes that have been used in the field. A general introduction to (poly)arylacetylenes, and the most common synthetic approaches directed toward making these materials will be firstly given. After a brief discussion on working principles and critical parameters of OPVs, we will focus on molecular arylacetylenes, (co)polymers containing triple bonds, and metallopolyyne polymers as p-type semiconductor materials. The last section will deal with hybrids in which oligomeric/polymeric structures incorporating acetylenic linkages such as phenylene ethynylenes have been attached onto C60, and their use as the active materials in photovoltaic devices

Experimental Technique for Traps Spatial Localization in GaN HEMTs

An experimental technique based on pulsed I-V measurement for the trap spatial localization within GaN-HEMTs is presented and discussed. By evaluating the dependence of the drain current-collapse versus the gate voltage base-line used for pulsed I-V measurement it is possible to spatially localize trap level responsible for the device performance degradation

Deep Levels Characterization in GaN HEMTs Part II: Experimental and Numerical Evaluation of Self-Heating Effects on the Extraction of Traps Activation Energy

none5In this paper, the effects of device self-heating on the extraction of traps activation energy are investigated through experimental measurements and numerical simulations. Neglecting the device temperature increase during the experimental measurements can lead to an underestimation of traps activation energies as well as nonoverlapping Arrhenius plots. It will be shown that said artifacts can be removed once device thermal resistance is known and used to correct the temperatures data points at which trap time constants are extracted. The correctness of the proposed method is also supported through numerical simulations carried out both by neglecting and considering thermal effects during the drain current transient measurements. Finally, the experimental results obtained are also suggesting a novel method for the extraction of device thermal resistance, which yielded comparable results with respect to those obtained with other experimental techniques.noneAlessandro Chini;Fabio Soci;Matteo Meneghini;Gaudenzio Meneghesso;Enrico ZanoniAlessandro, Chini; Fabio, Soci; Meneghini, Matteo; Meneghesso, Gaudenzio; Zanoni, Enric

Influence of device self-heating on trap activation energy extraction

none5In this paper results obtained by drain current transients measurement on GaN-based high electron mobility transistors (HEMTs) are presented. It will be shown that neglecting device self-heating effects during the calculation process can lead to an underestimation of said energies and to non-overlapping Arrhenius plots, when the emission time constants are extracted at different device dissipated power levels. Thanks to the estimation of the mean channel thermal resistance, thermal effects were taken into account by correcting the measured data. Higher activation energy values have then been extracted and a reasonable overlap of the Arrhenius plots was obtained amongst measurements carried out at different dissipated powers. The experimental results are also suggesting a novel method for the extraction of device thermal resistance, which yielded similar results with respect to other experimental techniques. © 2013 IEEE.noneF. Soci;A. Chini;G. Meneghesso;M. Meneghini;E. ZanoniF., Soci; A., Chini; Meneghesso, Gaudenzio; Meneghini, Matteo; Zanoni, Enric

Threshold voltage shift investigation and oxide trap profile extraction in AlGaN/GaN MIS-HEMTs

High breakdown voltage and low on-state resistance make AlGaN/GaN High Electron Mobility Transistors (HEMTs) very attractive for switching applications. However, because to its strong piezoelectric effect the conventional GaN HEMT structure is unsuitable for enhancement-mode (E-Mode) operation, which is usually required to improve the safety of the switching systems. In this work we present a GaN HEMT, where a gate recess in combination with Metal Insulator Semiconductor (MIS) structure have been used to obtain a positive threshold voltage (VTH). Insulator layer effectively helps to reduce the parasitic gate leakage currents, but unfortunately MIS-HEMT devices suffer of threshold voltage instability due to the charge trapping that occurs in the insulator layer [1,2,3]. Our aim is to investigate the trapping mechanisms in MIS-HEMT structure exploiting different characterization techniques

Effect of Gate Field-Plate Geometry on On-Resistance in AlGan/GaN HEMTs for Power Applications

On-resistance (RDSon) degradation is a well-known issue in AlGaN/GaN HEMTs technology for power applications [1,2], and is usually observed when the device is rapidly switched from off- to on-state condition. The introduction of field-plate terminals has proven to be a viable solution in order to mitigate the off-state electric fields and consequently improve the dynamic on-resistance behavior [2]. In this work the effect of different field-plate geometry will be investigated. Moreover, by using different characterization techniques, some insights on the trapping mechanisms causing the RDSon degradation will also be presented

Threshold voltage shift investigation and oxide trap profile extraction in AlGaN/GaN MIS-HEMTs

High breakdown voltage and low on-state resistance make AlGaN/GaN High Electron Mobility Transistors (HEMTs) very attractive for switching applications. However, because to its strong piezoelectric effect the conventional GaN HEMT structure is unsuitable for enhancement-mode (E-Mode) operation, which is usually required to improve the safety of the switching systems. In this work we present a GaN HEMT, where a gate recess in combination with Metal Insulator Semiconductor (MIS) structure have been used to obtain a positive threshold voltage (VTH). Insulator layer effectively helps to reduce the parasitic gate leakage currents, but unfortunately MIS-HEMT devices suffer of threshold voltage instability due to the charge trapping that occurs in the insulator layer [1,2,3]. Our aim is to investigate the trapping mechanisms in MIS-HEMT structure exploiting different characterization techniques

Correlation between Drain Current Transient and Double-Pulse Measurements in AlGaN/GaN HEMT Trap Analysis

Trap characterization represents an important step towards the improvement of the performances and reliability of GaN-based HEMT devices. Double-pulsed measurements and long drain current transient analysis are effective methods to gather complementary information on traps identification and localization: activation energy and time constant of the traps may be extrapolated through drain current transients measurements [1-3]; on the other hand, the analysis of the dynamic VTH shift and gm peak reduction, based on double-pulsed measurements, allows to understand whether the trap states are located below the gate (VTH shift) or in drain-gate access region (gm peak reduction) [4]. The aim of this work is to experimentally investigate the correlation between these two characterization techniques by applying them to a series of identical devices and comparing results on individual samples

Field plate related reliability improvements in GaN-on-Si HEMTs

State of the art GaN on Silicon HEMTs fabricated with and without a field-plate structure have been tested by means of DC and RF reliability tests. The introduction of the field-plate structure greatly improves device reliability both during DC as well as RF testing. Results are thus suggesting that reliability in NOFP and FP devices is mainly limited by the high electric fields within the device structure causing an increase in traps concentration

Ruxolitinib for pulmonary extramedullary hematopoiesis in myelofibrosis

Here we report an uncommon case of a patient with MF and pulmonary EMH treated with ruxolitini