Effect Of Auger Recombination Research Articles

Chemical Vapor Deposited Thin Palladium Sulfide Crystals for Highly Photoresponsive Photodetector

AbstractNonlayered palladium sulfide (PdS) is of interest due to its rich physical properties and promising applications in optoelectronic devices. However, the growth of thin nonlayered PdS remains challenging because of its intrinsic 3D lattice structure. Here, the first demonstration of the direct synthesis of thin rectangular PdS ribbons/flakes on SiO2/Si substrates by a facile chemical vapor deposition (CVD) approach is presented. The atomic structure and high crystalline quality of CVD‐derived PdS crystals are shown by scanning transmission electron microscopy. The nonlinear saturable absorption and absorption enhancement are revealed by using ultrafast optical pump‐probe spectroscopy, and the photocarrier dynamics present the hot phonon bottleneck and Auger recombination effects. Additionally, the Raman vibration modes display the polarization‐dependent properties verified by angle‐resolved polarized Raman spectroscopy. Importantly, the photodetector based on PdS ribbon demonstrates a decent photoresponsivity of ≈7.7 × 103 A W−1. This results provide an effective way to form thin nonlayered PdS with potential applications in the field of photodetection.

Charge transport dynamics and emission response in quantum-dot light-emitting diodes for next-generation high-speed displays

Inorganic quantum-dot light-emitting diodes (QD-LEDs) have gained significant attention as optoelectronic devices for next-generation display systems due to their superior colour properties. A comprehensive understanding of the charge transport dynamics and transient emission responses of the QD-LED is crucial to achieving high motion picture quality next-generation QD-LED display systems. In this study, we investigated the transient emission response of QD-LED devices through an advanced charge transport simulation model tailored to the quantum-dots (QDs). The dynamic response of the QD-LED devices is evaluated using the time-resolved electroluminescence measurement method for both cadmium-based and cadmium-free red, green, and blue QD-LEDs. The QD-LED devices exhibit notable emission drops during pulse voltage application. The charge transport simulation quantitatively reveals that the on and off switching speeds and the emission drops are intricately influenced by the electron and hole injection balance and a combination of carrier recombination factors within the QD layer. The charge transport simulation also shows that space-charge accumulation, due to the combined effects of charge imbalance and Auger recombination, quantitatively explains a potential device degradation mechanism. Therefore, the QD-specified charge transport model provides a crucial approach in designing and optimizing QD-LED devices for next-generation high-speed QD-LED displays with ultimate colour quality and long lifetimes.

Slow Hot-Exciton Cooling and Enhanced Interparticle Excitonic Coupling in HgTe Quantum Dots.

Rapid hot-carrier/exciton cooling constitutes a major loss channel for photovoltaic efficiency. How to decelerate the hot-carrier/exciton relaxation remains a crux for achieving high-performance photovoltaic devices. Here, we demonstrate slow hot-exciton cooling that can be extended to hundreds of picoseconds in colloidal HgTe quantum dots (QDs). The energy loss rate is 1 order of magnitude smaller than bulk inorganic semiconductors, mediated by phonon bottleneck and interband biexciton Auger recombination (BAR) effects, which are both augmented at reduced QD sizes. The two effects are competitive with the emergence of multiple exciton generation. Intriguingly, BAR dominates even under low excitation fluences with a decrease in interparticle distance. Both experimental evidence and numerical evidence reveal that such efficient BAR derives from the tunneling-mediated interparticle excitonic coupling induced by wave function overlap between neighboring HgTe QDs in films. Thus, our study unveils the potential for realizing efficient hot-carrier/exciton solar cells based on HgTe QDs. Fundamentally, we reveal that the delocalized nature of quantum-confined wave function intensifies BAR. The interparticle excitonic coupling may cast light on the development of next-generation photoelectronic materials, which can retain the size-tunable confinement of colloidal semiconductor QDs while simultaneously maintaining high mobilities and conductivities typical for bulk semiconductor materials.

Ultrasmall CsPbBr3 Blue Emissive Perovskite Quantum Dots Using K-Alloyed Cs4PbBr6 Nanocrystals as Precursors.

We report a colloidal synthesis of blue emissive, stable cube-shaped CsPbBr3 quantum dots (QDs) in the strong quantum confinement regime via dissolution-recrystallization starting from pre-syntesized (K x Cs1-x )4PbBr6 nanocrystals which are then reacted with PbBr2. This is markedly different from the known case of Cs4PbBr6 nanocrystals that react within seconds with PbBr2 and get transformed into much larger, green emitting CsPbBr3 nanocrystals. Here, instead, the conversion of (K x Cs1-x )4PbBr6 nanocrystals to CsPbBr3 QDs occurs in a time span of hours, and tuning of the QD size is achieved by adjusting the concentration of the precursors. The QDs exhibit excitonic features in optical absorption that are tunable in the 420-452 nm range, accompanied by blue photoluminescence with quantum yield around 60%. Detailed spectroscopic investigations in both the single and multiexciton regime reveal the exciton fine structure and the effect of Auger recombination of these CsPbBr3 QDs, confirming theoretical predictions for this system.

Optimization of Doping Levels and Emitter Thickness in Silicon Solar Cells to Minimize Auger Recombination Effects

Optimization of Doping Levels and Emitter Thickness in Silicon Solar Cells to Minimize Auger Recombination Effects

Effects of impact ionization and Auger recombination on hot-carrier solar cells and hot-carrier photocatalysts

We applied hot-carrier extraction to solar cells and photocatalysts used for artificial photosynthesis including water splitting and CO2 reduction, and elucidated the differences between these two applications: hot-carrier solar cells (HC-SCs) and hot-carrier photocatalysts (HC-PCs) by detailed balance calculations. The hot-carrier effect in the photocatalysts is less significant than that in the solar cells, because of the larger bandgaps required for generating sufficiently high-energy carriers consumed for the reactions. On the other hand, impact ionization and Auger recombination (IA) improves the efficiency of the HC-PCs more notably, because the IA functions like photon upconverters and hence narrows the optimal bandgap. Furthermore, the IA improves the spectral robustness by eliminating the constraint of the particle-number conservation for both the HC-SCs and HC-PCs. These benefits of the IA are contrasting with the well-recognized fact that the IA only reduces the carrier number and consequently lowers the efficiency of the conventional counterparts.

Understanding Auger recombination in perovskite solar cells.

Enhanced radiative efficiency, long carrier lifetimes, and high carrier mobilities are hallmarks of perovskite solar cells. Considering this, complete cells experience large nonradiative recombination losses that restrict their VOC considerably below the Shockley-Queisser limit. Auger recombination, which involves two free photo-induced carriers and a trapped charge carrier, is one potential mechanism. Herein, the effects of Auger capture coefficients in mixed-cation perovskites are analyzed employing SCAPS-1D computations. It is demonstrated that VOC and FF are severely decreased with an increase in the acceptor concentration and Auger capture coefficients of perovskites, thus reducing the device performance. When the Auger capture coefficient is increased to 10-20 cm6 s-1 under the acceptor concentration of 1016 cm-3, the performance is drastically lowered from 21.5% (without taking Auger recombination into account) to 9.9%. The findings suggest that in order to increase the efficiency of perovskite solar cells and prevent the effects of Auger recombination, the Auger recombination coefficients should be less than 10-24 cm6 s-1.

Boron‐doped polysilicon using spin‐on doping for high‐efficiency both‐side passivating contact silicon solar cells

AbstractThis study focuses on boron‐doped p+polysilicon (poly‐Si) passivating contacts using spin‐on doping (SOD). Experimental conditions, including annealing conditions, SOD concentration, and poly‐Si thickness, were controlled to improve passivation. Based on the analysis results, the passivation quality mainly changes with indiffusion and doping concentration, causing Auger recombination and field effects. Meanwhile, grain size also influences the passivation quality but showed marginal characteristics. Through further optimization using an etch back and diffusion barrier, the efficiency of the flat reference solar cell was improved to 17.5% with an open‐circuit voltage of 695 mV using a p+ poly‐Si contact emitter, the highest reported efficiency using SOD on saw‐damage‐etched surfaces. This study includes a detailed analysis of SOD p+ poly‐Si and shows promising results with potential for application in tandem devices. Furthermore, the cell efficiency is expected to increase by controlling the doping profile and application of textured surfaces, selective emitters, and forming gas annealing (FGA).

N-polar InGaN nanowires: breaking the efficiency bottleneck of nano and micro LEDs

The efficiency of conventional quantum well light-emitting diodes (LEDs) decreases drastically with reducing areal size. Here we show that such a critical size scaling issue of LEDs can be addressed by utilizing N-polar InGaN nanowires. We studied the epitaxy and performance characteristics of N-polar InGaN nanowire LEDs grown on sapphire substrate by plasma-assisted molecular beam epitaxy. A maximum external quantum efficiency ∼11% was measured for LEDs with lateral dimensions as small as 750 nm directly on wafer without any packaging. The effect of electron overflow and Auger recombination on the device performance is also studied. This work provides a viable approach for achieving high-efficiency nano and micro LEDs that were not previously possible.

Effect of 150 keV Ti+ ion implantation on the structural, optical, and electrical properties of nonstoichiometric WO2.72 thin films

WO2.72 thin films were deposited on fluorine-doped tin oxide substrates using the e-beam evaporation technique, and 150 keV Ti+ ions were implanted at various fluences. The structural studies of these thin films confirm the presence of P21/m monoclinic phase. After implantation, the intensities of X-ray peaks varied significantly, and atomic force microscopy images revealed changes in grain size with realignments and surface roughness. The redshift observed in the calculated bandgaps is due to the bandgap narrowing effect. The photoluminescence (PL) study shows the decrease in the PL intensity after implantation due to an increase in nonradiative and Auger recombination effects. The electrical studies exhibit the semiconductor to metal transition in Ti-implanted films at the highest ion fluence. The decreasing trend of resistivity, accompanied by the decrease in the carrier concentration, and the higher mobility is understood based on various scattering mechanisms.

Effect of Auger recombination on transient optical properties in XUV and soft X-ray irradiated silicon nitride

Spatially encoded measurements of transient optical transmissivity became a standard tool for temporal diagnostics of free-electron-laser (FEL) pulses, as well as for the arrival time measurements in X-ray pump and optical probe experiments. The modern experimental techniques can measure changes in optical coefficients with a temporal resolution better than 10 fs. This, in an ideal case, would imply a similar resolution for the temporal pulse properties and the arrival time jitter between the FEL and optical laser pulses. However, carrier transport within the material and out of its surface, as well as carrier recombination may, in addition, significantly decrease the number of carriers. This would strongly affect the transient optical properties, making the diagnostic measurement inaccurate. Below we analyze in detail the effects of those processes on the optical properties of XUV and soft X-ray irradiated Si{_3}N_4, on sub-picosecond timescales. Si{_3}N_4 is a wide-gap insulating material widely used for FEL pulse diagnostics. Theoretical predictions are compared with the published results of two experiments at FERMI and LCLS facilities, and with our own recent measurement. The comparison indicates that three body Auger recombination strongly affects the optical response of Si{_3}N_4 after its collisional ionization stops. By deconvolving the contribution of Auger recombination, in future applications one could regain a high temporal resolution for the reconstruction of the FEL pulse properties measured with a Si{_3}N_4-based diagnostics tool.

Feasibility of lasing in the GaAs Reststrahlen band with HgTe multiple quantum well laser diodes

Operation of semiconductor lasers in the 20–50 µm wavelength range is hindered by strong non-radiative recombination in the interband laser diodes, and strong lattice absorption in GaAs-based quantum cascade structures. Here, we propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. Using a comprehensive model accounting for carrier drift and diffusion, electron and hole capture in quantum wells, Auger recombination, and heating effects, we show the feasibility of lasing at λ = 26, …, 30 µm at temperatures up to 90 K. The output power in the pulse can reach up to 8 mW for microsecond-duration pulses.

Effect of recombination process in femtosecond laser-induced modification on Ge crystal* *Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 11804227).

The dynamics of produced excited carriers under the irradiation of Ge crystal is investigated theoretically by using femtosecond laser pulse. A two-temperature model combined with the Drude model is also used to study the nonequilibrium carrier density, carrier and lattice temperatures, and optical properties of the crystal. The properties of the surface plasmon wave when excited are also studied. The influences of non-radiation and radiative recombination process on the photoexcitation of the semiconductor during pulse and the relaxation after the pulse are described in detail. The results show that the effects of Auger recombination on the nonequilibrium carrier density and optical properties of the crystal and the properties of the surface plasmon polariton are great, whereas the effect of radiative recombination is extremely small.

Nitride dot-in-nanowire light emitters with suppressed auger process

In wurtzite III-Nitride nano-devices, the non-radiative Auger recombination is the primary mechanism responsible for the degradation of internal quantum efficiency (IQE), especially under high current density. In this paper, by employing an atomistic tight-binding framework, we theoretically study the effects of Auger recombination in recently reported InGaN/GaN dot-in-nanowire light emitters. The effects of strain and polarization, which can be strong in realistically-sized structures, have been considered. We demonstrate that the use of graded interfacial confinement leads to a weaker Auger recombination as compared to the abrupt counterpart, especially for thinner nanowires. The atomistically simulated Auger recombination coefficient for the core quantum dot buried in nanowire with different diameter is then incorporated into a TCAD simulator to obtain the device terminal (efficiency vs. current) characteristics. Overall, the simulation results indicate that increasing the diameter of the host nanowire (that is, the volume of the active region) remains the most efficient way to suppress Auger recombination.

Polarized near-infrared intersubband absorptions in CdSe colloidal quantum wells

Colloidal quantum wells are two-dimensional materials grown with atomically-precise thickness that dictates their electronic structure. Although intersubband absorption in epitaxial quantum wells is well-known, analogous observations in non-epitaxial two-dimensional materials are sparse. Here we show that CdSe nanoplatelet quantum wells have narrow (30–200 meV), polarized intersubband absorption features when photoexcited or under applied bias, which can be tuned by thickness across the near-infrared (NIR) spectral window (900–1600 nm) inclusive of important telecommunications wavelengths. By examination of the optical absorption and polarization-resolved measurements, the NIR absorptions are assigned to electron intersubband transitions. Under photoexcitation, the intersubband features display hot carrier and Auger recombination effects similar to excitonic absorptions. Sequenced two-color photoexcitation permits the sub-picosecond modulation of the carrier temperature in such colloidal quantum wells. This work suggests that colloidal quantum wells may be promising building blocks for NIR technologies.

Effect of Auger recombination in ensemble of CdSe nanocrystals on their luminescence

The temperature dependence of the photoluminescence intensity of colloidal CdSe nanocrystals having 5 nm in diameter was studied. It was demonstrated that the photoluminescence intensity exhibits a hysteresis at temperatures below 220 K. This effect was explained by a model taking into account formation of an additional nonradiative relaxation channel associated with Auger recombination promoted by hole trapping on the surface of the nanocrystals. The activation energy of the hole release process obtained in the framework of the model was 0.7 eV.

Effect of Auger recombination induced by donor and acceptor states on luminescence properties of silicon quantum Dots/SiO2 multilayers

Impurity doping is a key factor that needs to be addressed to control the optical properties of silicon quantum dots (Si QDs) for their applications in optoelectronic devices. Although there have been several studies to understand the effect on n-type and p-type dopant on the luminescence properties of Si QDs, the exact influence of the dopant impurities on the optical properties and the underlying mechanism are yet to be understood. For this purpose, we investigate the luminescence properties of Si QDs/SiO2 multilayer structure doped with B and P. Using rf-magnetron sputtering and ion implantation techniques, we prepared three kinds of samples: undoped, B-doped and P-doped. Results from photoluminescence measurements indicate that the significant luminescence suppression in the doped samples can be mainly attributed to the Auger non-radiative process occurring between photoexcited excitons and free carriers. Our interpretation should serve to resolve the controversy around the effect of impurity doping on the luminescence properties of Si QDs.

First-Principles Understanding of Strong Auger Recombination in Hybrid Perovskites

The radiative recombination coefficient of the hybrid perovskites is as high as in typical direct-gap semiconductors [1], facilitating strong light absorption in solar cells and potentially enabling their application in light-emitting diodes (LEDs). Since LEDs operate at higher carrier densities than solar cells, higher-order electron–hole recombination processes can critically affect their efficiency. We have computed Auger recombination coefficients in the prototypical halide perovskite [2], CH3NH3PbI3 (MAPbI3), using first‐principles calculations. Our computed nonradiative Auger coefficients show that strong Auger recombination may suppress the LED’s efficiency. Fortunately, our insights into the origins of the strong Auger recombination indicate potential avenues for engineering to reduce the effect of Auger recombination. This work was supported by DOE. [1] Zhang, X, et al. ACS Energy Lett. 3, 2329 (2018). [2] Shen, J.-X., et al. Adv. Energy Mater. 8, 1801027 (2018).

Thermoluminescence governed by the Auger-recombination process

In the present work, we study the possibility that a thermoluminescence (TL) peak is governed by the effect of Auger recombination, an effect which has been considered for other luminescence phenomena. In Auger recombination in the form of interest here, two conduction-band electrons are involved in the recombination of one of them with a hole in a center. The two electrons collide in the presence of the center, one loses energy and recombines, yielding a TL photon, and the other gains energy and speeds away. As mentioned with regard to other luminescence phenomena, in this case, in the set of differential equations governing this process, a term proportional to the square of the free-electron concentration should be included in analogy to the law of mass action. The relevant set of simultaneous differential equations has been solved numerically for feasible sets of parameters. The results yield a relatively narrow TL peak which is somewhat asymmetric, with the fall-off half being larger than the low-temperature half. Under appropriate conditions, the set of equations is shown to reduce to an approximate third-order kinetic equation, the solution of which has a very similar symmetry. The third-order approximate curve has an effective activation energy which is twice as large as the original. Such asymmetric peaks have been described in the literature. Also, when using standard peak-shape methods for evaluating the effective activation energy and frequency factor very high values of these magnitudes have been found due to the narrowness of the simulated peak. This model may explain the occurrence of such TL peaks previously reported in the literature. Also is discussed the possible concurrent regular Randall-Wilkins recombination and Auger recombination within the one-trap-one-recombination center (OTOR) model. In another version of the model, an additional thermally disconnected trap is considered. With certain sets of parameters, the simulations yield a cubic dependence of TL intensity on the excitation dose, an effect previously reported in some materials.

The effects of intraband and interband carrier‐carrier scattering on hot‐carrier solar cells: A theoretical study of spectral hole burning, electron‐hole energy transfer, Auger recombination, and impact ionization generation

AbstractThe effects of carrier‐carrier scattering resulting from the Coulomb‐potential interaction between two electrons on hot‐carrier solar cells are theoretically studied. Theoretical models and explicit formulas for calculating intraband carrier‐carrier scattering rates, electron‐to‐hole energy transfer rates, Auger recombination rates, and impact ionization generation rates are presented and derived. The numerical calculations from these formulas are obtained, and their effects on hot‐carrier solar cells are investigated. Several findings can be concluded from this study: (1) Intraband electron‐electron scattering and hole‐hole scattering are normally fast enough to randomize carrier distribution in the momentum space and thus maintain quasiequilibrium to establish electron and hole temperatures at a steady state; (2) spectral hole burning in hot‐carrier solar cells can be incurred by fast carrier extraction processes through energy‐selective contacts and slow intraband carrier‐carrier scattering; (3) energy transfer between electrons and holes via intraband electron‐hole scattering cannot guarantee that electrons and holes will maintain the same carrier temperature for hot‐carrier solar cells in all cases, especially if the difference between electron and hole temperatures is smaller than 100 K; and (4) materials with a band‐gap energy larger than 1 eV are favorable as conventional solar cells in which Auger recombination is not significant. On the contrary, materials with a band‐gap energy smaller than 0.5 eV are not suitable for conventional solar cells due to the detrimental effects of Auger recombination. However, they are ideal materials for realizing hot‐carrier solar cells due to beneficial effects of impact ionization generation, although these beneficial effects can be undermined by spectral hole burning.