Abstract
A picosecond acoustic pulse is used to study the photoelastic interaction in single zinc-blende GaN/AlxGa1−xN quantum wells. We use an optical time-resolved pump-probe setup and demonstrate that tuning the photon energy to the quantum well’s lowest electron-hole transition makes the experiment sensitive to the quantum well only. Because of the small width, its temporal and spatial resolution allows us to track the few-picosecond-long transit of the acoustic pulse. We further deploy a model to analyze the unknown photoelastic coupling strength of the quantum well for different photon energies and find good agreement with the experiments.
Highlights
During the last decade, picosecond acoustics have shown the ability for characterizing various nanostructures with nanometer and picosecond spatial and temporal resolution, respectively [1]
The temporal signals SðtÞ recorded for a pump excitation density W 1⁄4 W0 ∼ 1 mJ=cm2 are shown in Fig. 2(a) for three probe wavelengths λ. Their fast Fourier transforms (FFTs) presented in Fig. 2(b) show a spectral line, whose maximum fB increases slightly with the decrease of the wavelength λ from fB 1⁄4 112 GHz at λ 1⁄4 380 nm to fB 1⁄4 118 GHz at λ 1⁄4 370 nm. This spectral line is attributed to the so-called Brillouin oscillations, which appear in thick films due to the dynamic interference between the part of the probe beam being reflected from the picosecond strain pulse and from the surface of the sample [15]
We show experimentally that a highquality single quantum wells (QWs) of c-GaN is capable of detecting picosecond strain waves
Summary
Picosecond acoustics have shown the ability for characterizing various nanostructures with nanometer and picosecond spatial and temporal resolution, respectively [1]. There are different methods to optically detect subterahertz and terahertz (THz) elastic waves (i.e., coherent phonons) with picosecond temporal resolution. They can be observed at the surface of bulk materials by optical transitions covering a broad spectral range from the ultraviolet (UV) to the near infrared [2]. Nitride semiconductor QWs [e.g., GaN=ðInGaÞN] are highly efficient nanostructures for the generation and detection of coherent phonons with frequencies of up to 2 THz [6]. Most of the experiments with nitride quantum wells are performed on multiple QWs based on wurtzite (hexagonal) h-GaN and its alloys. We show that for a high x and an appropriate optical probing wavelength, the QW serves as a detector for subterahertz
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