Carrier dynamics and coherent acoustic phonons in nitride heterostructures

TL;DR

This paper models the generation and propagation of coherent acoustic phonons in nitride heterostructures, revealing their impact on optical signals and demonstrating control via delayed pulses.

Contribution

It introduces a comprehensive model for coherent phonon dynamics in InGaN/GaN quantum wells, highlighting the dominant piezoelectric mechanism and optical control methods.

Findings

Coherent acoustic phonons significantly modulate reflectivity signals.

Piezoelectric electron-phonon interaction is the primary phonon generation mechanism.

Optical control of reflectivity oscillations is achievable with delayed pulses.

Abstract

We model generation and propagation of coherent acoustic phonons in piezoelectric InGaN/GaN multi-quantum wells embedded in a \textit{pin} diode structure and compute the time resolved reflectivity signal in simulated pump-probe experiments. Carriers are created in the InGaN wells by ultrafast pumping below the GaN band gap and the dynamics of the photoexcited carriers is treated in a Boltzmann equation framework. Coherent acoustic phonons are generated in the quantum well via both deformation potential electron-phonon and piezoelectric electron-phonon interaction with photogenerated carriers, with the latter mechanism being the dominant one. Coherent longitudinal acoustic phonons propagate into the structure at the sound speed modifying the optical properties and giving rise to a giant oscillatory differential reflectivity signal. We demonstrate that coherent optical control of the differential reflectivity can be achieved using a delayed control pulse.