Cerenkov generation of high-frequency confined acoustic phonons in quantumwells

We analyze the Cerenkov emission of high-frequency confined acoustic phonon s by drifting electrons in a quantum well. We find that the electron drift can cause strong phonon amplification (generation). A general formula for t he gain coefficient alpha is obtained as a function of the phonon frequency and the structure parameters. The gain coefficient increases sharply in th e short-wave region. For the example of a Si/SiGe/Si device, it is shown th at the amplification coefficients of the order of hundreds of cm(-1) can be achieved in the subterahertz frequency range. (C) 2000 American Institute of Physics. [S0003-6951(00)00514-3].