We discuss the basic properties of the transient hot-electron transport and dynamic mobility in group-III nitrides under dominant electron-polar-optical-phonon scattering determining their capability for applications in THz frequency range. For bulk samples with high electron concentration, we provide the phaseplane analysis of the time-dependent transient transport and classification of different transient regimes depending on the initial conditions. The calculations predict a frequency interval with negative dynamic electron mobility where the amplification and generation of microwaves in THz frequency range is possible. For quantum-well heterostructures with low electron concentration under the streaming regime at moderate fields, we have revealed THz frequency windows of the negative microwave mobility, which enables the development of a tunable THz laser based on nitride quantum heterostructures.
IntroductionThe group-III nitrides are known to demonstrate a set of unique fundamental material properties [1, 2] which have renewed interest in different high-field regimes in these materials. Specific features of the electron band structure and electron-phonon interaction characterized by strong electronoptical phonon coupling and large optical phonon energy (ћω op ~ 90 meV) can be used for realization of electrically pumped high-frequency generators operating in terahertz frequency diapason. In this work, we focus on the analysis of hot-electron transport regimes important for the nitrides: transient dynamics at high dc electric fields and dynamic mobility in bulk-like structures; the streaming transport regime and dynamic mobility in quantum wells (QWs) with two-dimensional (2D) electrons at moderate fields. We determine the conditions for a negative high-frequency electron mobility, which indicate perspective applications of the nitrides for ultra-high speed devices as well as the development of THz generators.