Picosecond Acoustics in Single Quantum Wells of Cubic GaN/(Al,Ga)N

Abstract

A picosecond acoustic pulse is used to study the photoelastic interaction in single zinc-blende GaN=Al x Ga 1−x N 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.

Photoelastic properties of zinc-blende AlxGa1−xN in the UV: Picosecond ultrasonic studies

“…From [28] and references therein we may estimate the uncertainty of defining photoelastic constants to be ∼20% and so in the interest of prudence we present only the first significant digit for α and β in Table I. The quantitative calculation of the reflectivity changes R(t)/R 0 (R 0 : reflectivity at η = 0) can be performed on the basis of analytical [19,22] or numerical [16] approaches. We estimate the maximum amplitude of the Brillouin oscillations using the equations for R(t)/R 0 derived in [19].…”

“…In our case, when R(t) strongly depends on λ, we shall consider only the case when dynamical strain induces the modulation of E g . For η 1 we have [16] …”

“…Picosecond ultrasonics was previously used to study the photoelastic properties of h-GaN and related nanostructures [13]. More recently, a few experiments have been carried out on c-GaN layers [14], c-GaN membranes [15], and c-GaN/AlGaN quantum wells [16].…”