Study of confined coherent acoustic phonon modes in a free-standing cubic GaN membrane by femtosecond spectroscopy

Abstract

Confined longitudinal coherent acoustic phonon modes are excited and detected in a sub-lm-thick free-standing cubic GaN membrane by femtosecond pump-probe spectroscopy. After fs laser excitation, Brillouin oscillation and thickness oscillation with frequencies up to 100 GHz are observed and studied in the time domain. We found an initial expansion of the membrane upon optical excitation at 400 nm. Our experimental results confirmed earlier existing theoretical predictions and experimental observations that the hydrostatic deformation potential of cubic GaN is positive. V C 2015 AIP Publishing LLC. [http://dx

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

“…These oscillations are due to the fundamental vibrational mode of the membrane. The modes with higher frequency are not observed in our experiments because of their much smaller amplitude which agrees with earlier studies on pure c-GaN membranes [15]. The left inset in Fig.…”

“…(1). The straight line connects the values of sound velocities measured in c-GaN [14,15] and calculated for c-AlN [20]. It is seen that the values for s a obtained from the experiment and Eq.…”

“…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].…”

Coherent acoustic phonons in van der Waals nanolayers and heterostructures

“…A number of recent works have focused on twodimensional (2D) nanometer-thick layers where phonons are quantized in the direction perpendicular to the 2D plane. Examples include submicrometer free-standing membranes based on Si [43], GaAs [44] and GaN [45], and phonon nanocavities [46].…”

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

“…Experiments with zinc-blende (cubic) c-GaN, which does not possess piezoelectricity along the high-symmetry directions (e.g. [100]), were performed only on bulk layers [7,8]. The importance of c-GaN QWs in picosecond acoustics is related to the possibility of embedding c-GaN QWs into Si-or GaAs-based phononic chips, thus, allowing us to perform phononic engineering for nanoscopy [9] and electrophononic devices [10].…”