Enhancement Of Carrier Injection Research Articles

Current imbalance analysis of multichip influenced by parasitic inductance within PP-IEGT

The Press-Pack Injection Enhanced Gate Transistor (PP-IEGT) technology is frequently employed in converters for high power systems. In the device packaging, the imbalanced current sharing among chips has become a significant issue for device reliability. Considering the semiconductor structure of IEGT is different from the conventional power devices, the main prerequisite for fully quantifying the current distribution is to establish a suitable electrical model for IEGT. Thus, this paper proposes an IEGT single chip lumped-charge model taking into account the effect of carrier injection enhancement in the emitter. Furthermore, as for the parallel branches in PP-IEGT, the parasitic inductance of the drive board and pillars within the package are extracted by Ansys simulation, and the validity of Ansys simulation is verified by the port S-parameter method. Finally, combining the electrical model and the effect of mutual inductance, the switching inconsistency is evaluated. It is demonstrated that the farther the branch from the gate inlet, the greater the gate inductance withstands. Besides, the mutual inductance is an important factor to influence the electrical parameter distribution. Both mutual coupling coefficient and current density display degressive trends with the increases of the gap between parallel chips.

High-color-rendering-index phosphor-free InGaN-based white light-emitting diodes by carrier injection enhancement via V-pits

We herein report the growth of phosphor-free InGaN-based white light-emitting diodes (LEDs) by metalorganic vapor-phase epitaxy. The active region consists of blue and red InGaN quantum wells (QWs). To improve the current injection and generate broadband emission, the V-pit structures in the LEDs were fabricated intentionally before growing the QWs. The monolithic white LEDs emit in the range of 410–770 nm and, by tuning the injection current, can cover correlated color temperature (CCT) values corresponding to warm white, natural white, and cool white. The color-rendering index (CRI) of the white LEDs reaches 88 at an injection current of 10 mA. At an injection current of 30 mA, the white LEDs exhibit the chromaticity coordinates of (0.320 and 0.334) in the Commission Internationale de l'Eclairage 1931 chromaticity diagram, a CRI of 78, and a CCT of 6110 K.

Reduction in efficiency droop/decline of green GaN-based light-emitting diodes by employing heterostructure cap layer

In this study, we theoretically studied the enhancement of carrier injection by employing heterostructure layers before p-GaN in green light-emitting diodes. It is evident from the simulation results that improved carrier injection results in high internal quantum efficiency and light output power in the structures using heterostructures on the p-side. In comparison to conventional structure, reduced efficiency droop is observed suggesting promising high-performance green light-emitting diodes.

Attosecond optical-field-enhanced carrier injection into the GaAs conduction band

Resolving the fundamental carrier dynamics induced in solids by strong electric fields is essential for future applications, ranging from nanoscale transistors1,2 to high-speed electro-optical switches3. How fast and at what rate can electrons be injected into the conduction band of a solid? Here, we investigate the sub-femtosecond response of GaAs induced by resonant intense near-infrared laser pulses using attosecond transient absorption spectroscopy. In particular, we unravel the distinct role of intra- versus interband transitions. Surprisingly, we found that despite the resonant driving laser, the optical response during the light–matter interaction is dominated by intraband motion. Furthermore, we observed that the coupling between the two mechanisms results in a significant enhancement of the carrier injection from the valence into the conduction band. This is especially unexpected as the intraband mechanism itself can accelerate carriers only within the same band. This physical phenomenon could be used to control ultrafast carrier excitation and boost injection rates in electronic switches in the petahertz regime. Significant enhancement of carrier injection into the conduction band is observed for GaAs subjected to intense resonant near-infrared laser pumping. Attosecond-resolved investigation reveals the interplay between the intra- and interband transitions.

Characteristics of carrier injection on polarization-dependent photoexcitation in copper phthalocyanine thin films

The carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam. The modulation efficiency of terahertz transmission due to transverse-magnetic (TM)-polarized excitation is distinctly higher than that due to transverse-electric (TE)-polarized excitation. Underlying this difference is the enhancement of carrier injection when the TM-polarized light is more transmitted through the surface of organic thin films than the TE-polarization light.

Improving light-emitting electrochemical cells with ionic additives

Light-emitting electrochemical cells with ionic transition metal complexes (iTMCs) comprising the active layer have great potential for lighting applications, but to date high luminance and fast turn on times have been challenging to attain without significant loss of lifetime. Here, we demonstrate iridium iTMC devices with high luminances of 3000–5000 cd/m2, reduced turn on times, and long lifetimes through incorporation of ionic additives. Furthermore, we show additional reduction of turn on time to seconds through heat processing. We rationalize these results as the enhancement of carrier injection through improved double-layer formation at the electrodes.

LiF Layer at the Interface of Au Cathode in Organic Light-Emitting Devices: A Nonchemical Induced Carrier Injection Enhancement

Au is not a suitable cathode material of organic light-emitting device because of its high work function resulting in poor electron injection. However, in present work, it is found that the performance of Au-cathode OLEDs can be efficiently improved by introducing a LiF buffer layer and with its optimal thickness can even be comparable to that of conventional Al-cathode device. The relationship between the thickness of LiF layer and the performance improvement is investigated. The experimental results indicate a quite different mechanism of LiF thin layer from that of Al-cathode device, which is not chemical-reaction-mechanism-dominant. Other insulator material buffer layers such as Al2O3 and BCP are also investigated.

Improving organic light-emitting diode performance with patterned structures

The influence nano- and micro- structures on light extraction and carrier injection characteristics in organic light-emitting diodes (OLEDs) is examined. The results demonstrate device enhancement from two distinctive patterning scales: embedded microstructure arrays for improved light extraction and imprinted nanostructures for carrier injection enhancement. Further, based on these results, a two-level imprinting stamp is designed which simultaneously produces a micron-sized pattern for facilitating light extraction and a nanometer-sized pattern to improve carrier injection. Additionally, this scalable patterning technology circumvents imprinting misalignment while preserving its compatibility with rollto- roll technology.

Current Characteristics of Pristine and Tetrathianaphthacene-Doped Tris(8-Hydroxyquinoline) Aluminum (ALQ3) Thin Films

We report our study on the current-voltage characteristics of single layer devices employing pure and heavily tetrathianaphthacene (TTN)-doped tris(8-hydroxy-quinoline) aluminum (Alq3) films as active layers. Sandwich structures with magnesium (Mg) top and bottom electrodes were employed in the devices. In the undoped device, the current increases exponentially with the applied voltage, and is concluded to be limited by the carrier injection at the Mg/Alq3 interface with a small injection barrier. With the same device structure, both the bulk-doped and interface-doped devices show a bulk-limited current flow, which is much larger than that in the undoped device and behaves as trap-free space-charge-limited current (SCLC) with a field-independent mobility. The improvement of the current is ascribed to the large enhancement of carrier injection by the doping. An increase of the magnitude of the interfacial dipole has been proposed as the possible cause for the enhancement of carrier injection.

Ni ∕ Au contact to silicon quantum dot light-emitting diodes for the enhancement of carrier injection and light extraction efficiency

The effect of Ni∕Au metal contact on the carrier injection and the electroluminescence of silicon quantum dot light-emitting diodes (LEDs) was investigated. An LED with an annealed Ni∕Au contact at 400°C in air showed a lower threshold voltage compared to that of an as-deposited Ni∕Au contact by forming a nickel silicide, which has a lower work function than Ni at the interface between metal layers and silicon nitride. The optical output power of the LED with the annealed Ni∕Au contact was also increased due to a highly transparent NiO layer and a lowly resistant Au layer.

Anodization of electrolytically polished Ta surfaces for enhancement of carrier injection into organic field-effect transistors

Electrolytically polished surfaces of Ta sheets were anodized in an aqueous KI solution to form Ta2O5 films with a relatively high dielectric constant and a high breakdown electric field. Organic field-effect transistors (OFETs) were fabricated on these Ta2O5∕Ta substrates with a bottom gate configuration. The Ta2O5 films anodized at 100V were about 200nm thick, and the dielectric strength was as high as 5MV∕cm. A p-type pentacene OFET fabricated on this bottom gate showed the good field-effect mobility of 0.35cm2∕Vs. By using this high-k gate substrate, it becomes possible to inject a higher amount of charge carriers into organic active layers than on the SiO2∕Si gate conventionally used in most OFETs.