Runaway effects in nanoscale group-III nitride semiconductor structures

We have revisited the problem of electron runaway in strong electric fields in polar semiconductors focusing on nanoscale group-III nitride structures. By developing a transport model that accounts for the main features of electrons injected in short devices under high electric fields, we have investigated the electron distribution as a function of electron momenta and coordinates. Runaway transport is analyzed in detail. The critical field of this regime is determined for InN, GaN, and AlN. We found that the transport in the nitrides is always dissipative (i.e., no ballistic transport). For the runaway regime, however, the electrons increase their velocities with distance, which results in average velocities higher than the peak velocity in bulklike samples. We have demonstrated that the runaway electrons are characterized by a distribution function exhibiting a population inversion.