Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate

We study the interaction of Dirac Fermions in monolayer graphene on a GaAs substrate in an applied electric field by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (piezoelectric acoustical (PA)) and of the intrinsic deformation potential of acoustical phonons in graphene (deformation acoustical (DA)). We find that provided the dc field exceeds a threshold value, emission of piezoelectric (PA) and deformation (DA) acoustical phonons can be obtained in a wide frequency range up to terahertz at low and high temperatures. We found that the phonon amplification rate R-PA,R-DA scales with T-BG(S-1)(S = PA, DA), T-BG(S) being the Block - Gruneisen temperature. In the high-T Block - Gruneisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio R-PA/R-DA scales with approximate to 1/root n, n being the carrier concentration. We found that only for carrier concentration n <= 10(10) cm(-2), R-PA/R-DA > 1. In the low-T Block - Gruneisen regime, and for n = 10(10) cm(-2), the ratio R-PA/R-DA scales with T-BG(DA)/T-BG(PA) approximate to 7.5 and R-PA/R-DA > 1. In this regime, PA phonon dominates the electron scattering and R-PA/R-DA < 1 otherwise. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device. (C) 2014 AIP Publishing LLC.