Effect Of Auger Recombination Research Articles

Enhancement of the band edge emission of CdSe nano-tetrapods by suppression of surface trapping.

Preparation of CdSe nano-tetrapods in a controlled environment, using a glove box for the preparation of the Se precursor, was found to eliminate radiative surface trap emission to a large extent. This manifested in an increase in the band edge photoluminescence quantum yield by a factor of 20 and a concomitant decrease in the surface trap emission by a factor of 8. Interestingly, the time for recovery of ground state bleaching was more or less the same in the two kinds of nano-tetrapods, even though the photoluminescence dynamics are significantly slower in the more emissive ones. In single emissive nano-tetrapods, the kinetic traces for ground state bleaching recovery became gradually faster upon increasing the pump power. This is likely to be due to the effect of multiexciton relaxation and nonradiative Auger recombination.

Publisher’s Note: “Degradation effect of Auger recombination and built-in polarization field on GaN-based light-emitting diodes” [AIP Advances 8, 015005 (2018)

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Degradation effect of Auger recombination and built-in polarization field on GaN-based light-emitting diodes

In this work, theoretical investigation of the influence of Auger recombination coefficient and built-in polarization field on the internal quantum efficiency (IQE) in terms of lateral-vertical single quantum well (SQW) as well as multiquantum well (MQW) GaN-based blue light-emitting diodes are presented. The degradation effect of the built-in polarization field on the IQE of vertical light-emitting diodes is used to strengthening the Auger recombination coefficient in comparison to lateral light-emitting diodes. This result has been found consistent in both single-as well as multi-quantum well structures. In addition, when Auger recombination coefficient has been included in the analysis, vertical multiquantum well structure shows more degradation in the IQE in comparison to the lateral structures. The effect has been dominant in vertical MQW case.

The effect of Auger recombination on the nonequilibrium carrier recombination rate in the InGaAsSb/AlGaAsSb quantum wells

Time dependencies of interband photoluminescence are studied in InGaAsSb/AlGaAsSb quantum well structures with various barrier materials and quantum well widths. The experimentally determined dependencies of photoluminescence intensity on the optical pumping level are compared with calculated dependencies of photoluminescence intensity on the nonequilibrium carrier concentration. Time of charge carrier trapping into quantum wells and the energy relaxation time related to the polar optical phonon emission were obtained from analysis of the photoluminescence dynamics at different optical pumping levels. The recombination rates with respect to nonradiative Shockley–Read–Hall and Auger recombination were determined. It is shown that, at certain parameter sets, resonant Auger recombination can exist in InGaAsSb/AlGaAsSb quantum well structures, which should results in the decrease of the concentration of carriers taking part in the radiative recombination.

Ultrafast structural dynamics of boron nitride nanotubes studied using transmitted electrons.

We investigate the ultrafast structural dynamics of multi-walled boron nitride nanotubes (BNNTs) upon femtosecond optical excitation using ultrafast electron diffraction in a transmission electron microscope. Analysis of the time-resolved (100) and (002) diffraction profiles reveals highly anisotropic lattice dynamics of BNNTs, which can be attributed to the distinct nature of the chemical bonds in the tubular structure. Moreover, the changes in (002) diffraction positions and intensities suggest that the lattice response of BNNTs to the femtosecond laser excitation involves a fast and a slow lattice dynamic process. The fast process with a time constant of about 8 picoseconds can be understood to be a result of electron-phonon coupling, while the slow process with a time constant of about 100 to 300 picoseconds depending on pump laser fluence is tentatively associated with an Auger recombination effect. In addition, we discuss the power-law relationship of a three-photon absorption process in the BNNT nanoscale system.

Extended storage of multiple excitons in trap states of semiconductor nanocrystals

Owing to the Auger recombination effect, multiple excitons (MEs) in semiconductor nanocrystals (NCs) are dissipated nonradiatively at the sub-nanosecond time scale, which sets a stringent limit on the time window within which one can operate with them. Here, we show that this issue can be resolved by utilizing an intrinsic energy transfer system in CdSe NCs, where MEs created in the donor quantized states can be effectively extracted to the acceptor trap states. This was evidenced by the step-like increase in the intensity and the apparent decrease in the rise time of the trap-state photoluminescence with the elevated laser excitation power. With the radiative lifetime being tens of nanoseconds for the trap states, extended storage of MEs has been achieved and marks a crucial step towards flexible manipulations of their optoelectronic properties.

Study on limiting efficiencies of a-Si:H/μc-Si:H-based single-nanowire solar cells under single and tandem junction configurations

Detailed balance calculations are presented for a-Si:H/μc-Si:H-based single- and tandem-junction single-nanowire solar cells (S- and T-SNSCs). Our study is based on three-dimensional finite-element electromagnetic simulation and thermodynamic balanced analysis, which includes radiative and Auger recombinations simultaneously. We quantify and compare the limiting short-circuit current densities, open-circuit voltages, and light-conversion efficiencies of these highly compact photovoltaic cells, addressing especially the effect of Auger recombination on the open-circuit voltages of SNSCs. Results show that tandem design leads to much higher light-conversion capability than μc-Si:H S-SNSCs, but exhibits superior performance than a-Si:H S-SNSCs only for cells with large radii.

Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell Interfaces.

Nanocrystal quantum dots (QDs) are attractive materials for applications as laser media because of their bright, size-tunable emission and the flexibility afforded by colloidal synthesis. Nonradiative Auger recombination, however, hampers optical amplification in QDs by rapidly depleting the population of gain-active multiexciton states. In order to elucidate the role of Auger recombination in QD lasing and isolate its influence from other factors that might affect optical gain, we study two types of CdSe/CdS core/shell QDs with the same core radii and the same total sizes but different properties of the core/shell interface ("sharp" vs "smooth"). These samples exhibit distinctly different biexciton Auger lifetimes but are otherwise virtually identical. The suppression of Auger recombination in the sample with a smooth (alloyed) interface results in a notable improvement in the optical gain performance manifested in the reduction of the threshold for amplified spontaneous emission and the ability to produce dual-color lasing involving both the band-edge (1S) and the higher-energy (1P) electronic states. We develop a model, which explicitly accounts for the multiexciton nature of optical gain in QDs, and use it to analyze the competition between stimulated emission from multiexcitons and their decay via Auger recombination. These studies re-emphasize the importance of Auger recombination control for the realization of real-life QD-based lasing technologies and offer practical strategies for suppression of Auger recombination via "interface engineering" in core/shell structures.

Auger recombination at low temperatures in InGaAs/InAlAs quantum well probed by photoluminescence

This paper reports abnormal effects of Auger recombination in InGaAs/InAlAs quantum well probed by steady state temperature and excitation-power dependent photoluminescence measurements. The transition from Auger recombination to Shockley–Read–Hall recombination is clearly manifested with rising temperature, and abnormal enhancement of Auger recombination at low temperatures is evidenced. Detailed analysis indicates that such enhancement is positively correlated with strong localization, and can be either relative and due to reduction of Shockley–Read–Hall recombination, or absolute and resulted from the confinement-induced uncertainty of momentum. It suggests that excitation-power dependent photoluminescence measurement is effective to assess the side-effect of the localization, and therefore a convenient evaluation routine of alloy quantum wells.

Counterbalanced Effect of Surface Trap and Auger Recombination on the Transverse Terahertz Carrier Dynamics in Silicon Nanowires

The surface-trap mediated carrier recombination is a crucial feature in characterizing the optoelectronic properties of nanowires (NWs). Due to the one-dimensional characteristics, the photoexcited carriers experiences multiple carrier interactions in the transverse direction such that strong carrier-carrier interactions are expected to play an important role in the NW carrier recombination. Here, using ultrafast optical-pump and terahertz-probe spectroscopy, we show that the Auger scattering significantly reduces the trap-mediated decay process. Systematic studies on bulk Si, bundled, individual, and encapsulated (reduced surface-trap density) SiNWs reveal that the effect of Auger recombination exhibits strong pump-fluence dependence depending on the surface-treatment condition.

Excitation and relaxation dynamics in dielectrics irradiated by an intense ultrashort laser pulse

When transparent dielectrics are irradiated by an intense, ultrashort laser pulse, the electron density in the conduction band is increased tremendously. Simultaneously, valence band states become unoccupied and the electron–phonon coupling strength is increased. In this paper, we present our work on modeling the ultrafast nonequilibrium dynamics of laser-excited transparent dielectrics with Boltzmann collision integrals. We track the distribution function of conduction and valence band electrons and discuss the effects of Auger recombination in relation to impact ionization and multiphoton/tunnel ionization on the femtosecond timescale. Finally, we investigate the electron–phonon coupling strength in highly excited dielectrics and calculate the electron–phonon coupling parameter for silicon dioxide-like material.

Effect of Auger recombination and leakage on the droop in InGaN/GaN quantum well LEDs.

We investigate the effect of the epitaxial structure and the acceptor doping profile on the efficiency droop in InGaN/GaN LEDs by the physics based simulation of experimental internal quantum efficiency (IQE) characteristics. The device geometry is an integral part of our simulation approach. We demonstrate that even for single quantum well LEDs the droop depends critically on the acceptor doping profile. The Auger recombination was found to increase stronger than with the third power of the carrier density and has been found to dominate the droop in the roll over zone of the IQE. The fitted Auger coefficients are in the range of the values predicted by atomistic simulations.

Investigation on Switching Energy Losses in Reversely Switched Dynistor

This paper presents theoretical and experimental results on the energy loss characteristics of reversely switched dynistor (RSD) under high-current conditions. Theoretical analysis was performed based on a 1-D modified model by taking account into the carrier-carrier scattering effect and auger recombination effect during the conducting process. The experimental results of energy losses in RSD at various amplitudes of high pulse current were accurately obtained using the direct current injection method. The typical experimental results show that a single RSD has a voltage drop of approximately 9 V with a pulse current of 150 kA, transferred charge of 26.5 C. The theoretical calculated voltage drop based on 1-D modified model is approximately 7.7 V under the same conditions. The theoretical results based on the 1-D modified model almost agree well with the experimental results.

Overcoming Auger recombination in nanocrystal quantum dot laser using spontaneous emission enhancement

We propose a method to overcome Auger recombination in nanocrystal quantum dot lasers using cavity-enhanced spontaneous emission. We derive a numerical model for a laser composed of nanocrystal quantum dots coupled to optical nanocavities with small mode-volume. Using this model, we demonstrate that spontaneous emission enhancement of the biexciton transition lowers the lasing threshold by reducing the effect of Auger recombination. We analyze a photonic crystal nanobeam cavity laser as a realistic device structure that implements the proposed approach.

The role of electron-electron interaction in the process of charge-carrier capture in deep quantum wells

The role of electron-electron interaction in the process of electron capture to a deep quantum well is investigated. Using two-level and three-level quantum wells as examples, the basic electron-capture mechanisms, i.e., the interaction with optical phonons and the Coulomb electron-electron interaction, are considered, and the corresponding capture probabilities and electron lifetimes are calculated. The effect of Auger recombination on the charge-carrier distribution in a quantum well is also taken into account. With this taken into consideration, a set of rate equations is solved for a nonsteady-state mode, and the time dependences of the electron concentration at the ground energy level in the quantum well are found. The contributions of each of the recombination processes under consideration are shown.

Resonance coulomb trapping of electrons in a deep quantum well

The role of the Coulomb interaction in trapping of electrons in a deep quantum well is investigated. By an example of a three-level quantum well, the fundamental mechanisms of trapping of electrons are considered: upon interaction with optical phonons and Coulomb interaction of electrons with one another. The corresponding trapping probabilities and lifetimes of electrons are calculated. With regard to the effect of Auger recombination on the charge-carrier distribution in a quantum well, the system of rate equations for the nonstationary regime is solved and the time dependences of electron concentrations at the ground energy level in the quantum well are determined. The contribution of each recombination process is shown.

Interplay of polarization fields and Auger recombination in the efficiency droop of nitride light-emitting diodes

We use theoretical modeling to investigate the effect of polarization fields and non-radiative Auger recombination on the efficiency-droop and green-gap problems of polar and nonpolar nitride light-emitting diodes. The dependence of radiative and nonradiative recombination rates on electron-hole wave-function overlap is analyzed. Device designs that minimize the polarization fields lead to higher efficiency, not because the internal quantum efficiency is improved at a given carrier density but because they can be operated at a lower carrier density for a given current density.

Effect of active QW population on optical characteristics of polar, semipolar and nonpolar III-nitride light emitters

Quantum well (QW) population effects are compared in III-nitride light emitters with different levels of polarity. We show that wider nonpolar active QWs are characterized by increased QW transparency current and a reduced differential optical gain which consequently increases the laser threshold. We also show that high intra-QW recombination rates in nonpolar/semipolar structures make the QW populations strongly non-equilibrium and vulnerable to inhomogeneous QW injection. In the LED regime, structures with a different polarity level reveal different mechanisms of the efficiency droop. In polar structures, the droop is dominated by the electron leakage and is notably affected by the active region ballistic overshoot. The efficiency droop in semipolar/nonpolar structures is dominated by the combined effect of radiative time saturation and non-radiative Auger recombination.

Injection efficiency and optical gain characteristics of polar and nonpolar III‐nitride light emitters

AbstractOptical properties of III‐nitride quantum well (QW) structures grown on nonpolar or semipolar crystallographic planes benefit from reduced internal fields in QWs and, as a result, from enhanced overlap between electron and hole states participating in lasing transition. Detailed modelling of active QWs shows, however, that smaller separation of the lasing states from the high‐energy subbands in nonpolar QWs and related thermal carrier redistribution between subbands can reduce the QW differential optical gain thus increasing the laser threshold. Efficiency characteristics of multiple QW emitters are additionally affected by inhomogeneous QW injection and by large residual QW charges. Polar and nonpolar light‐emitting diode structures reveal different mechanisms of the efficiency droop. In polar structures, the droop is dominated by electron leakage and is noticeably affected by the active region ballistic overshoot. Efficiency droop in nonpolar structures is dominated by combined effect of radiative time saturation and nonradiative Auger recombination while the carrier leakage becomes a factor of secondary importance. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Implementation of Highly Resistive Emitter Solar Cells in a Production Environment using an Inline Doping System

Instead of selective emitter technology we investigate an alternative way to optimize contact formation and increased blue responsivity of highly resistive emitter solar cells using screen print technology for the deposition of the frontside metallization grid. We show with the aid of an inline doping/diffusion set-up at Blue Chip Energy that tuning the emitter doping profile is an alternative way to reduce the effect of Auger recombination in the spectral range from 300 nm to 600 nm. By properly choosing the process conditions we were able to minimize the detrimental effect of the low surface concentration of the dopant on the contact resistance. Due to improved blue light responsivity a significant gain in short circuit current Jsc was achieved. This and a reduced reverse saturation current I00E yielded a higher open circuit voltage VOC and an increase of cell efficiency from 17.6 %-avg to more than 17.9 %-avg.