Influence of nitrogen on coherent longitudinal optical phonons in GaAs1− <i>x</i> N <i>x</i>

We investigated the influence of nitrogen (N) on coherent longitudinal optical (LO) phonons in dilute nitride semiconductor alloys. Terahertz time-domain spectroscopy reveals a reduced frequency (redshift) of LO phonons and enhanced decay times for coherent GaAs-like LO phonons emitted from GaAs1−xNx in comparison to those from semi-insulating GaAs. We attribute the redshift of the phonon frequency to both N-alloying-induced compression of the As-sublattice and tensile coherency strain at the GaAs1−xNx/GaAs interface. In addition, an N-induced enhancement of the coherent phonon decay time is attributed to reduced LO phonon scattering associated with the enhanced electron effective masses that reduce the transient electron velocity.