Despite the great amount of attention CH3NH3PbI3 has received for its solar cell application, intrinsic properties of this material are still largely unknown. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. We apply this method to characterize a CH3NH3PbI3 single crystal. We measure the acoustic phonon properties and characterize electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. Our results reveal high electron and hole mobilities of 2,800 and 9,400 cm2 V−1 s−1, respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH3NH3PbI3. Carrier mobility is a basic semiconductor property. Manteet al., use femtosecond lasers to investigate coherent acoustic phonons and relate their deformation potentials to estimate the intrinsic electron and hole mobilities of CH3NH3PbI3 single crystals to be 2,800 and 9,400 cm2 V−1 s−1, respectively.

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Electron–acoustic phonon coupling in single crystal CH3NH3PbI3 perovskites revealed by coherent acoustic phonons

Exact solutions to the electromechanical quantities inside a statically-bent circular ZnO nanowire by taking into account both the piezoelectric property and the semiconducting performance: Part I--Linearized analysis

We report on the acoustic attenuation in an AlPdMn icosahedral quasicrystal between 15 and 300 K, in the tens of GHz range. High frequency coherent longitudinal acoustic waves are excited and detected by an optical ``pump and probe'' technique, in an interferometric configuration. Our results reveal that, at high temperature $(Tg100\mathrm{K}),$ the acoustic attenuation is rather small, close to the attenuation in crystals and much smaller than in disordered solids. We stress that Akhieser processes (phonon-phonon interactions) must be active in quasicrystals and give the correct behavior and order of magnitude of the acoustic attenuation, at high temperature. At low temperature, departure from the standard behavior arising from phonon-phonon interaction is not understood.

Ultrasonic attenuation in a quasicrystal studied by picosecond acoustics as a function of temperature and frequency

Adjustment and control on the fundamental characteristics of a piezoelectric PN junction by mechanical-loading

Terahertz (THz) and sub-THz coherent acoustic phonons have been successfully used as probes of various quantum systems. Since their wavelength is in the nanometer range, they can probe nanostructures buried below a surface with nanometer resolution and enable control of electrical and optical properties on a picosecond time scale. However, coherent acoustic phonons have not yet been widely used to study van der Waals (vdW) two-dimensional (2D) materials and heterostructures. This class of 2D systems features strong covalent bonding of atoms in the layer planes and weak van der Waals attraction between the layers. The dynamical properties of the interface between the layers or between a layer and its supporting substrate are often omitted as they are difficult to probe. On the other hand, these play a crucial role in interpreting experiments and/or designing new device structures. Here we use picosecond ultrasonic techniques to investigate phonon transport in vdW InSe nanolayers and InSe/hBN heterostructures. Coherent acoustic phonons are generated and detected in these 2D systems and allow us to probe elastic parameters of different layers and their interfaces. In particular, our study of the elastic properties of the interface between vdW layers reveals a strong coupling over a wide range of frequencies up to 0.1 THz, offering prospects for high-frequency electronics and technologies that require control over the charge and phonon transport across an interface. In contrast, we reveal a weak coupling between the InSe nanolayers and sapphire substrates, relevant in thermoelectrics and sensing applications, which can require quasi-suspended layers.

https://link.aps.org/pdf/10.1103/PhysRevB.98.075408

Coherent acoustic phonons in van der Waals nanolayers and heterostructures

THz acoustic phonon spectroscopy and nanoscopy by using piezoelectric semiconductor heterostructures

We demonstrate that guided acoustic waves inside a nanorod can be excited through an external metallic acoustic transducer. By attaching gold nanodisks on top of GaAs nanorods, the femtosecond optical excitation on the external acoustic transducer enables the generation of guided acoustic waves in the rods. The propagation behavior and mode shape of the observed guided acoustic waves are analyzed. These observations would not only lead to the development of superior external transducers for acoustic imaging, but also provide an experimental system for the study of the acoustic phonon transport behavior in nanorods and nanowires.

Efficient excitation of guided acoustic waves in semiconductor nanorods through external metallic acoustic transducer

In this paper we report that nanoacoustic pulses can modulate the extraordinary optical transmission (EOT) in nanogratings with a high frequency bandwidth. This study was performed on gold nanogratings on top of a GaN crystal by combining a near-field scanning optical microscope with a femtosecond nanoultrasonic system. Experimental results indicate that the propagating longitudinal nanoacoustic pulses changed the refractive index of a GaN crystal and therefore modulated the near-field cavity mode behavior. Our finding suggests that the temporal modulation with a >11GHz bandwidth can be achieved, with a high potential for future temporal and high speed control on the EOT behavior in nanostructures.

Szu Chi Yang

Papers

THz acoustic phonon spectroscopy and nanoscopy by using piezoelectric semiconductor heterostructures

Efficient excitation of guided acoustic waves in semiconductor nanorods through external metallic acoustic transducer

Near-field dynamic study of the nanoacoustic effect on the extraordinary transmission in gold nanogratings