Measurement of Ambipolar Diffusion Coefficient of Photoexcited Carriers with Ultrafast Reflective Grating-Imaging Technique

Chen, Ke; Sheehan, Nathanial; He, Feng; Meng, Xianghai; Mason, Sarah C.; Bank, Seth R.; Wang, Yaguo

doi:10.1021/acsphotonics.7b00187

Cited by 11 publications

(13 citation statements)

References 32 publications

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“… 21 , the time resolution was limited to ~0.5 ns which prevented measurements at smaller grating period where second sound is expected at much higher temperatures. In this work, we replaced the CW laser with a femtosecond pulsed laser and used the standard ultrafast measurement technique in which the pump-probe delay time is varied to acquire time-dependent signals 43 , 44 . The experimental details can be found in Material and methods and the Supplementary Materials (SM1).…”

Section: Resultsmentioning

confidence: 99%

Observation of second sound in graphite over 200 K

et al. 2022

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Second sound refers to the phenomenon of heat propagation as temperature waves in the phonon hydrodynamic transport regime. We directly observe second sound in graphite at temperatures of over 200 K using a sub-picosecond transient grating technique. The experimentally determined dispersion relation of the thermal-wave velocity increases with decreasing grating period, consistent with first-principles-based solution of the Peierls-Boltzmann transport equation. Through simulation, we reveal this increase as a result of thermal zero sound—the thermal waves due to ballistic phonons. Our experimental findings are well explained with the interplay among three groups of phonons: ballistic, diffusive, and hydrodynamic phonons. Our ab initio calculations further predict a large isotope effect on the properties of thermal waves and the existence of second sound at room temperature in isotopically pure graphite.

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Section: Resultsmentioning

confidence: 99%

Observation of second sound in graphite over 200 K

et al. 2022

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“…Figure 2(a) shows that the peak of the ∆R/R 0 signal is proportional to the pump fluence, and the signals measured at different pump fluences overlap when normalized (as shown in the inset), which indicates that the pump fluences used in our experiments are small enough that the ∆R/R 0 value is linear with the excited carrier density. 20 Figure 2(b) shows the transient differential ∆R/R 0 signals of MBE MoTe 2 measured at different pump fluences. The signals are exponential decays superposed with clear periodic oscillations, which are the coherent acoustic phonons (strain pulse) generated by the pump laser and will be discussed later.…”

Section: -2mentioning

confidence: 99%

“…The magnitude of ∆R/R 0 signals is also proportional to the pump fluence, and the normalized signals overlap as shown in the inset, indicating that the pump fluence is low enough to ensure a linear relation between the value of ∆R/R 0 signals and the excited carrier density plus the phonon vibration amplitude. 20 The comparison of ∆R/R 0 signals in exfoliated and MBE MoTe 2 is shown in Fig. 2(c).…”

Section: -2mentioning

confidence: 99%

Accelerated carrier recombination by grain boundary/edge defects in MBE grown transition metal dichalcogenides

et al. 2018

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“…Studying carrier diffusion process can also reveal carrier scattering in semiconductors, assess carrier mobility with Einstein relation, and understand interactions between carriers and phonons, defects, and nanostructures. Currently, there are several optical techniques to measure the carrier diffusion coefficients nondestructively: transient grating [1,2], spatial scanning pump-probe [3,4], and grating imaging [5,6]. In the transient grating method, two pump beams overlap on the sample surface to generate a transient carrier density grating.…”

Section: Introductionmentioning

confidence: 99%

Comparison between Grating Imaging and Transient Grating Techniques on Measuring Carrier Diffusion in Semiconductor

Chen

Meng

et al. 2018

Nanoscale and Microscale Thermophysical Engineering

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Optical grating technique, where optical gratings are generated via light inference, has been widely used to measure charge carrier and phonon transport in semiconductors. In this paper, compared are three types of transient optical grating techniques: transient grating diffraction, transient grating heterodyne, and grating imaging, by utilizing them to measure carrier diffusion coefficient in a GaAs/AlAs superlattice. Theoretical models are constructed for each technique to extract the carrier diffusion coefficient, and the results from all three techniques are consistent. Our main findings are: (1) the transient transmission change ∆T/T0 obtained from transient grating heterodyne and grating imaging techniques are identical, even these two techniques originate from different detection principles; and (2) By adopting detection of transmission change (heterodyne amplification) instead of pure diffraction, the grating imaging technique (transient grating heterodyne) has overwhelming advantage in signal intensity than the transient grating diffraction, with a signal intensity ratio of 315:1 (157:1). I. INTRODUCTIONCarrier diffusion in semiconductors is crucial in electronic and opto-electronic devices, since it determines some key parameters of the devices, such as working frequency and response time.Studying carrier diffusion process can also reveal carrier scattering in semiconductors, assess carrier mobility with Einstein relation, and understand interactions between carriers and phonons, defects, and nanostructures. Currently, there are several optical techniques to measure the carrier diffusion coefficients nondestructively: transient grating [1,2], spatial scanning pump-probe [3,4], and grating imaging [5,6]. In the transient grating method, two pump beams overlap on the sample surface to generate a transient carrier density grating. A probe beam shines on the grating and the diffracted probe is taken as the signal, which reflects the decaying process of the carrier density grating. In the spatial scanning pump-probe technique, both the pump and probe beams are tightly focused onto the sample surface. The pump generates a Gaussian-shape carrier package and the probe is scanned spatially across the pump spot. By measuring the differential transmission or reflection (∆T/T0 or ∆R/R0) of the probe as a function of time and position, the evolution of the carrier package, which contains the information of carrier diffusion, is recorded. In the grating imaging technique, pump and probe beams overlap on a physical transmission amplitude grating (a photomask with metal strips patterned onto a glass substrate), whose image is formed by an objective lens onto the surface of the sample. The intensities of pump and probe beam on the sample are modulated in the same pattern as the transmission amplitude grating. The pump generates transient carrier grating in the sample, while the probe only detects the evolution of carrier density in the bright-strip regions. By measuring either ∆T/T0 or ∆R/R0 of the probe as a function o...

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Measurement of Ambipolar Diffusion Coefficient of Photoexcited Carriers with Ultrafast Reflective Grating-Imaging Technique

Cited by 11 publications

References 32 publications

Observation of second sound in graphite over 200 K

Observation of second sound in graphite over 200 K

Accelerated carrier recombination by grain boundary/edge defects in MBE grown transition metal dichalcogenides

Comparison between Grating Imaging and Transient Grating Techniques on Measuring Carrier Diffusion in Semiconductor

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