Non-equilibrium longitudinal optical phonons and their lifetimes

Non-equilibrium phonons have been discussed for almost six decades. Here, the nature of the longitudinal optical mode, particularly in polar materials, is discussed along with its lifetime and bottleneck occurrences. The history of non-equilibrium phonons is discussed along with their generation by the relaxation of hot carriers. The role of inter-valley scattering and phonon lifetime is introduced along with the concept of a phonon bottleneck. Various methods of lifetime measurement are introduced. Measurements of the lifetime in a variety of semiconductor materials is reviewed and a possible scaling behavior discussed.