Intrinsic coherent acoustic phonons in the indirect band gap semiconductors Si and GaP

Abstract

We report on the intrinsic optical generation and detection of coherent acoustic phonons at (001)-oriented bulk Si and GaP without metallic phonon transducer structures. Photoexcitation by a 3.1-eV laser pulse generates a normal strain pulse within the ∼100-nm penetration depth in both semiconductors. The subsequent propagation of the strain pulse into the bulk is detected with a delayed optical probe as a periodic modulation of the optical reflectivity. Our theoretical model explains quantitatively the generation of the acoustic pulse via the deformation potential electronphonon coupling and detection in terms of the spatially and temporally dependent photoelastic effect for both semiconductors. Comparison with our theoretical model reveals that the strain pulses have finite build-up times of 1.2 and 0.4 ps for GaP and Si, which is comparable with the intervalley scattering time constant required for the photoexcited electrons to reach the conduction band minimum. The deformation potential coupling related to the acoustic pulse generation for GaP is estimated to be twice as strong as that for Si from our experiments, in agreement with a previous theoretical prediction.

Observation of Small Polaron and Acoustic Phonon Coupling in Ultrathin La0.7Sr0.3MnO3/SrTiO3 Structures

“…Optical Generated Coherent Acoustic Phonons : Now, we explain the generation of the acoustic phonons using the propagating strain pulse model . In this model, the pump beam induces a transient thermal lattice expansion due to laser heating.…”

Energy-dependent amplitude of Brillouin oscillations in GaP

“…Our data and K. Ishioka et al data are in a good agreement while the model underestimates the increase in the amplitude of Brillouin oscillations passed 2.4 eV. This is mostl due the fact that the tabulated dielectric function from D. Aspnes's paper does not resolve the feature near Γ point and, therefore, leads to a smeared energy derivative of dielectric function.This observation might explain the discrepancy observed by K. Ishioka et al35 .…”

“…In this paper, we report on an experimental study of probe energy dependence of the amplitude In this current study, we extend the range of the probe energy from the Ishioka et al 35 study from below the indirect band gap (2.26 eV) to well above the direct band gap (2.78 eV) of GaP.…”

“…shows our experimental data, the data from Ishioka et al35 and the model that utilizes dielectric function from Aspnes et al36 . The amplitude increases as the energy increases up to 2.76 eV (direct band gap of GaP).…”

Coherent optical and acoustic phonons generated at lattice-matched GaP/Si(0 0 1) heterointerfaces

“…This can be understood in terms of the poorer sensitivity of the visible probe light to the near surface region. The periodic modulation at f Si B dephases before the strain pulse goes out of the probe depth due to the broad bandwidth of the probe light [41]. Figure 8 plots the initial amplitude A 0 , obtained by fitting the reflectivity oscillations for t 10 ps to a damped harmonic function:…”