Ambipolar diffusion of photoexcited carriers in bulk GaAs

Ruzicka, Brian A.; Werake, Lalani K.; Samassekou, Hassana; Zhao, Hui

doi:10.1063/1.3533664

Cited by 79 publications

(58 citation statements)

References 32 publications

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“…A spatial Fourier analysis indicates the presence of grains up to 500 nm in diameter, with a mean grain size of 250 nm. The observation of L D ∼4 × larger than the mean grain diameter, together with the fact that this ambipolar diffusion length is limited by the slower carrier species, 42 indicates that grain boundaries do not constitute a significant barrier to carrier motion. This result is in agreement with recent measurements on solution processed CH 3 NH 3 PbI 3 using AC Photo Hall 25 and photocurrent imaging techniques 26 as well as theoretical calculations suggesting that the most prevalent point defects represent shallow traps and that grain boundaries have a relatively benign effect.…”

Section: −1 S Is Plotted Versus 8πmentioning

confidence: 98%

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Carrier diffusion in thin-film CH3NH3PbI3 perovskite measured using four-wave mixing

Webber

Clegg

Mason

et al. 2017

Applied Physics Letters

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We report the application of femtosecond four-wave mixing (FWM) to the study of carrier transport in solution-processed CH3NH3PbI3. The diffusion coefficient was extracted through direct detection of the lateral diffusion of carriers utilizing the transient grating technique, coupled with simultaneous measurement of decay kinetics exploiting the versatility of the boxcar excitation beam geometry. The observation of exponential decay of the transient grating versus interpulse delay indicates diffusive transport with negligible trapping within the first nanosecond following excitation. The in-plane transport geometry in our experiments enabled the diffusion length to be compared directly with the grain size, indicating that carriers move across multiple grain boundaries prior to recombination. Our experiments illustrate the broad utility of FWM spectroscopy for rapid characterization of macroscopic film transport properties.Organo-lead trihalide perovskites possess a unique combination of electronic and optical properties, making them attractive for applications in light-emitting diodes, 1,2 lasers, 3-5 optical sensors, 6-8 and most notably high performance solar cells where the efficiencies have rapidly increased, reaching over 22% in just a few years. 9In addition, these hybrid perovskites can be solutionprocessed and applied as thin films to a variety of substrates, 10,11 pointing to the potential for large-scale, low-cost solar cell production.12-16 The transport properties of electrons and holes within the perovskite absorber material are crucial to the performance of photovoltaics and other optoelectronic technologies using these materials. The first observation of micron-scale carrier diffusion lengths in CH 3 NH 3 PbI 3−x Cl x 17-19 stimulated a comprehensive research effort aimed at understanding the nature of carrier transport.20-33 Carrier mobilities and/or diffusion lengths have been studied using electrical techniques (e.g. AC Photo Hall, 25 spacecharge-limited current, 31 impedance spectroscopy, 21 , and spatially-resolved electron-beam-induced current 27 ) as well as optical techniques that rely on electrical contacts such as photoluminescence quenching 17,18 and scanning photocurrent microscopy.26,33 Some of these techniques offer the ability to probe transport in a working solar cell device, however imperfectly characterized interface energetics and ambiguities tied to the model-dependent extraction of transport characteristics impede the determination of the physical processes limiting device performance.All-optical techniques provide an effective approach to studying carrier transport within a wide range of photovoltaic materials as no carrier extraction layers or ohmic contacts are required. Time-domain terahertz spectroscopy (TDTHz) and time-resolved microwave conductivity (TRMC) have provided valuable insight into carrier scattering processes in the organometal halide perovskites in recent years. 24,28,29 For such techniques, the quantitative determination of mobility requires modeling of the...

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Section: −1 S Is Plotted Versus 8πmentioning

confidence: 98%

“…A third delayed pulse E 3 (t-(τ+T)), was used to probe the grating modulation depth by monitoring the diffracted signal as a function of time delay T between pulses E 2 and E 3 . Provided carrier transport is diffusive, 40,42 the FWM signal decays exponentially versus T, 40,41 with the signal intensity proportional to:…”

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confidence: 99%

Carrier diffusion in thin-film CH3NH3PbI3 perovskite measured using four-wave mixing

Webber

Clegg

Mason

et al. 2017

Applied Physics Letters

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“…Although ambipolar diffusion for band gap excitation into the Γ valley of GaAs has been studied [62,63], here we have to consider the case with a large transient population of carriers in the L and X valleys. In addition, the highest mobilities are typically known for undoped, semi-insulating material and the mobility drops greatly with doping due to ionized impurity scattering.…”

Section: Carrier Ambipolar Diffusionmentioning

confidence: 99%

Ultrafast coupling of coherent phonons with a nonequilibrium electron-hole plasma in GaAs

et al. 2015

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Abstract:We present a joint experimental-theoretical study of the coupling of coherent phonons in bulk GaAs with a nonequilibrium electron-hole plasma following photoexcitation at the E 1 gap by ultrafast laser pulses. In contrast to prior coherent phonon experiments where photoexcitation across the E 0 gap generated electrons in the Γ valley, for the E 1 gap excitation, the majority of the electrons are generated in the satellite L valleys. This leads to a drastically different situation from the previous studies where the damping of electrons is faster due to the higher scattering rates in the L valley and in addition, the diffusion of carriers has a significant effect on the plasma response due to the shorter optical absorption depth of the pump-probe light. Reflectivity measurements show coherent phonon-plasmon oscillations, whose frequencies are indicative of the heavy damping, which leads to coupled-mode frequencies that lie between the transverse and longitudinal optical phonon frequencies and change with time due to the diffusion of the plasma. We analyze the experimental data with a theoretical model that describes the time and densitydependent coupling of the coherent phonon and the electron-hole plasma as the photoexcited carriers diffuse into the sample on a sub-picosecond time scale. The calculated phonon-plasmon dynamics qualitatively reproduce the experimentally observed time-dependent frequency.

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“…After the initial work on electrostatic coupling between electrons and holes 1 , significant theoretical and experimental work has been published on ambipolar diffusion in bulk materials 2,3 as well as in heterostructures 4,5 . The majority of recent studies consider undoped material so that the ambipolar diffusion constant is only related to hole diffusion [6][7][8] or to excitonic transport 9 . The dependence of the ambipolar diffusion constant, D a = (D n σ p + D p σ n )/(σ p + σ n ), on the unipolar diffusion constant D n (D p ) of electrons (holes) and of their partial conductivities σ n (σ p ) has never been detailed experimentally.…”

Section: Introductionmentioning

confidence: 99%

Imaging ambipolar diffusion of photocarriers in GaAs thin films

Paget

Cadiz

Rowe

et al. 2012

Journal of Applied Physics

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Images of the steady-state luminescence of passivated GaAs self-standing films under excitation by a tightly-focussed laser are analyzed as a function of light excitation power. While unipolar diffusion of photoelectrons is dominant at very low light excitation power, an increased power results in a decrease of the diffusion constant near the center of the image due to the onset of ambipolar diffusion. The results are in agreement with a numerical solution of the diffusion equations and with a physical analysis of the luminescence intensity at the centre of the image, which permits the determination of the ambipolar diffusion constant as a function of electron concentration.

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Ambipolar diffusion of photoexcited carriers in bulk GaAs

Cited by 79 publications

References 32 publications

Carrier diffusion in thin-film CH3NH3PbI3 perovskite measured using four-wave mixing

Carrier diffusion in thin-film CH3NH3PbI3 perovskite measured using four-wave mixing

Ultrafast coupling of coherent phonons with a nonequilibrium electron-hole plasma in GaAs

Imaging ambipolar diffusion of photocarriers in GaAs thin films

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