Acoustic Amplification by Stimulated Emission of Radiation Using a Piezoelectric-2DEG Heterostructure Pumped by a Drift Field

We theoretically demonstrate a quantum acoustoelectric amplifier using a heterostructure consisting of a two-dimensional electron gas (2DEG) stacked on top of a piezoelectric material. An applied drift voltage effectively pumps the 2DEG electrons. Once an acoustic wave is launched, the pumped electrons release phonons via stimulated emission, returning to depleted ground states before being pumped back to the excited states. We show that whereas efficient amplification using a 1D electron gas requires the acoustic wavelength to roughly equal the average electron-electron spacing, a 2DEG enables efficient amplification for any wavelength greater than the average electron-electron spacing. We derive the imaginary and real parts of the 2DEG's first-order acoustic susceptibility (respectively representing the phonon emission rate per unit electric field intensity and the electric field intensity per phonon) as functions of electronic drift velocity in specific limits and synthesize these results to determine the gain per unit length for the signal and the quantum noise. Moreover, we analyze the gain clamping mechanisms and calculate the peak intensity for a given input intensity. Our results promise a breakthrough system that can serve as an acoustic equivalent of a maser or laser.