Proposed Measurement of the Acoustoelectric Effect by Electron-Photon-Phonon Interaction for Hypersonic Phonons in Semiconductors

Abstract

It is proposed that amplification of phonons of frequencies in the order of hundreds of gigahertz can be investigated by measuring expected changes in the free carrier absorption coefficient which will occur from changes in the density of thermal phonons. It is shown that for photon energies greater than the thermal energy, there is a one-to-one correspondence between the energy of the incident photons and the momentum of the phonons that are required for free carrier absorption by means of intraband electron transitions. An important result derived is that the phonon energy per unit bandwidth, at a particular phonon frequency proportional to the incident radiation energy, is directly related to the ratio of the free carrier absorption coefficients during and before acoustoelectric amplification. As a specific example, the case of CO2 laser radiation absorption in n-type Ge is considered, leading to the result that at 10 K the free carrier absorption coefficient will increase by several orders of magnitude over its thermal equilibrium value during acoustoelectric amplification. In addition, the dependence of the free carrier absorption coefficient on the phonon density suggests applications in some laser devices such as photon drag detectors and amplitude modulators.