Ultrafast Removal of LO-Mode Heat From a GaN-Based Two-Dimensional Channel

Dissipation of the Joule heat, accumulated in non-equilibrium longitudinal optical (LO) phonon modes, is considered in terms of LO-phonon lifetime. The dependence of the lifetime on electron density, hot-electron temperature, and supplied electric power are presented for a voltage-biased GaN-based channel with a two-dimensional electron gas (2DEG). An improved understanding of conversion of LO phonons into acoustic and other phonons is reached. A non-monotonous dependence of the lifetime on the electron density is observed. The optimal 2DEG density for ultrafast decay of the LO-mode heat is estimated and explained in terms of LO-phonon-plasmon resonance. A new limitation of the frequency performance is predicted for heterostructure field-effect transistors under the off-resonance conditions of operation. The shortest hot-phonon lifetime of $\sim \!\! 60\pm 20\ {\rm fs}$ is found, at a high level of supplied power, in nearly lattice-matched InAlN/AlN/GaN.