Hot phonons in high-field transport

The effect of hot-phonon production on the steady-state high-field transport properties of electrons in bulk and quasi-2D semiconductors is discussed within the framework of a simple theoretical model in which Cerenkov effects and phonon drift are assumed to be negligible. The model also assumes a single spherical parabolic band for the electrons whose distribution is a displaced Maxwellian, with scattering confined to polar optical phonons, restricted to interface modes in a deep square quantum well in the quasi-2D case. A finite phonon lifetime of 7 ps is shown to reduce the energy relaxation rate and to increase the momentum relaxation rate. The result is to lower the mobility and to delay runaway to higher fields, these effects increasing with the electron density. It is pointed out that nondrifting hot phonons tend to quench intervalley and real-space-transfer NDRS and to reduce the drift velocity for a given field. It is shown that, in general, the effective energy relaxation time is field dependent.