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1. Effects of high optical injection levels in polycrystalline Si wafers on carrier transport

   Steele, Doneisha ; Semichaevsky, Andrey ( March 2017 , Bulletin of the American Physical Society)

   High levels of carrier injection in polycrystalline Si may arise, for example, in solar cells under concentrated sunlight. Mechanisms for non-radiative carrier recombination include trap-mediated SRH and higher-order processes, e.g., Auger recombination [1]. In this paper we present our experimental results for intensity-dependent carrier lifetimes and conduction currents in polycrystalline Si wafers illuminated with pulses of up to 50 Sun intensity. We also use a computational model for carrier transport that includes both SRH and Auger recombination mechanisms, in order to explain our experiments. The model allows quantifying recombination rate dependence on carrier concentration. Our goal is to relate the recombination rates to Si microstructure and defect densities [2] that are revealed by IR PL images. We acknowledge the NSF support through grant 1505377. [1] A. Richter, S.W. Glunz, F. Werner, J. Schmidt, and A. Cuevas, Improved quantitative description of Auger recombination in crystalline silicon, Phys. Rev. B 86, 165202 (2012). [2] H. C. Sio, T. Trupke, D. Macdonald, Quantifying carrier recombination at grain boundaries in multicrystalline silicon wafers through photoluminescence imaging. J. Appl. Phys. 116, 244905 (2014). 

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2. Ab initio nonadiabatic molecular dynamics of charge carriers in metal halide perovskites

   https://doi.org/10.1039/d1nr01990b  

   Li, Wei ; She, Yalan ; Vasenko, Andrey S. ; Prezhdo, Oleg V. ( June 2021 , Nanoscale)

   Photoinduced nonequilibrium processes in nanoscale materials play key roles in photovoltaic and photocatalytic applications. This review summarizes recent theoretical investigations of excited state dynamics in metal halide perovskites (MHPs), carried out using a state-of-the-art methodology combining nonadiabatic molecular dynamics with real-time time-dependent density functional theory. The simulations allow one to study evolution of charge carriers at the ab initio level and in the time-domain, in direct connection with time-resolved spectroscopy experiments. Eliminating the need for the common approximations, such as harmonic phonons, a choice of the reaction coordinate, weak electron–phonon coupling, a particular kinetic mechanism, and perturbative calculation of rate constants, we model full-dimensional quantum dynamics of electrons coupled to semiclassical vibrations. We study realistic aspects of material composition and structure and their influence on various nonequilibrium processes, including nonradiative trapping and relaxation of charge carriers, hot carrier cooling and luminescence, Auger-type charge–charge scattering, multiple excitons generation and recombination, charge and energy transfer between donor and acceptor materials, and charge recombination inside individual materials and across donor/acceptor interfaces. These phenomena are illustrated with representative materials and interfaces. Focus is placed on response to external perturbations, formation of point defects and their passivation, mixed stoichiometries, dopants, grain boundaries, and interfaces of MHPs with charge transport layers, and quantum confinement. In addition to bulk materials, perovskite quantum dots and 2D perovskites with different layer and spacer cation structures, edge passivation, and dielectric screening are discussed. The atomistic insights into excited state dynamics under realistic conditions provide the fundamental understanding needed for design of advanced solar energy and optoelectronic devices. 

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3. Impact of doped barriers on the recombination coefficients of c -plane InGaN/GaN single quantum well light-emitting diodes

   https://doi.org/10.1063/5.0117318  

   Chow, Y. C. ; Lynsky, C. ; Nakamura, S. ; DenBaars, S. P. ; Weisbuch, C. ; Speck, J. S. ( November 2022 , Applied Physics Letters)

   Differential carrier lifetime measurements were performed on c-plane InGaN/GaN single quantum well (QW) light-emitting diodes (LEDs) of different QW indium compositions as well as with and without doped barriers. Mg-doped p-type and Si-doped n-type barriers close to the QW were used to reduce the net internal electric field in the QW, thereby improving the electron–hole wavefunction overlap on the LEDs. LEDs with doped barriers show short lifetimes and low carrier densities in the active region compared to the reference LEDs. The recombination coefficients in the ABC model were estimated based on the carrier lifetime and quantum efficiency measurements. The improvement in the radiative coefficients in the LEDs with doped barriers coupled with the blueshift of the emission wavelengths indeed indicates an enhancement in wavefunction overlap and a reduction of quantum confined Stark effect as a result of the reduced internal electric field. However, doped barriers also introduce non-radiative recombination centers and thereby increase the Shockley–Read–Hall (SRH) coefficient, although the increment is less for LEDs with high indium composition QWs. As a result, at high indium composition (22%), LEDs with doped barriers outperform the reference LEDs even though the trend is reversed for LEDs with lower indium composition (13.5%). Despite the trade-off of higher SRH coefficients, doped barriers are shown to be effective in reducing the internal electric field and increasing the recombination coefficients.

    

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4. Large Tolerance of Lasing Properties to Impurity Defects in GaAs(Sb)‐AlGaAs Core‐Shell Nanowire Lasers

   https://doi.org/10.1002/adfm.202311210  

   Schreitmüller, Tobias ; Jeong, Hyowon W. ; Esmaielpour, Hamidreza ; Mead, Christopher E. ; Ramsteiner, Manfred ; Schmiedeke, Paul ; Thurn, Andreas ; Ajay, Akhil ; Matich, Sonja ; Döblinger, Markus ; et al ( December 2023 , Advanced Functional Materials)

   GaAs‐AlGaAs based nanowire (NW) lasers hold great potential for on‐chip photonic applications, where lasing metrics have steadily improved over the years by optimizing resonator design and surface passivation methods. The factor that will ultimately limit the performance will depend on material properties, such as native‐ or impurity‐induced point defects and their impact on non‐radiative recombination. Here, the role of impurity‐induced point defects on the lasing performance of low‐threshold GaAs(Sb)‐AlGaAs NW‐lasers is evaluated, particularly by exploring Si‐dopants and their associated vacancy complexes. Si‐induced point defects and their self‐compensating nature are identified using correlated atom probe tomography, resonant Raman scattering, and photoluminescence experiments. Under pulsed optical excitation the lasing threshold is remarkably low (<10 µJ cm⁻²) and insensitive to impurity defects over a wide range of Si doping densities, while excess doping ([Si]>10¹⁹ cm⁻³) imposes increased threshold at low temperature. These characteristics coincide with increased Shockley‐Read‐Hall recombination, reflected by shorter carrier lifetimes, and reduced internal quantum efficiencies (IQE) . Remarkably, despite the lower IQE the presence of self‐compensating Si‐vacancy defects provides an improved temperature stability in lasing threshold with higher characteristic temperature and room‐temperature lasing. These findings highlight an overall large tolerance of lasing metrics to impurity defects in GaAs‐AlGaAs based NW‐lasers.

    

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5. Long interior carrier lifetime in selective-area InAs nanowires on silicon

   https://doi.org/10.1364/OME.403531  

   Zhang, Kailing ; Li, Xinxin ; Walhof, Alexander C. ; Liu, Yuzi ; Toor, Fatima ; Prineas, John P. ( September 2020 , Optical Materials Express)

   Catalyst-free, position-controlled indium arsenide (InAs) nanowires (NWs) of variable diameters were grown on Si (111) by selective-area epitaxy (SAE). Ultrafast pump-probe spectroscopy was conducted, from which carrier recombination mechanisms on the NW surface and interior were resolved and characterized. NWs grown using SAE demonstrated high optical quality, showing minority carrier lifetimes more than two-fold longer than that of the randomly-positioned (RP) NWs. The extracted SAE-InAs NW interior recombination lifetime was found to be as long as 7.2ns, 13X longer than previous measurements on RP-NWs; and the surface recombination velocity 4154cm·s^{- 1}. Transmission electron microscopy revealed a high density of stacking defects within the NWs, suggesting that interior recombination lifetime can be further increased by improving NW interior crystalline quality.

    

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