Terahertz oscillations in gallium nitride quantum-well channels predicted by hot-electron noise temperature behavior at microwave frequency

Abstract

The almost periodic streaming motion of accelerated electrons under moderate electric fields coupled with almost periodic emission of longitudinal optical (LO) phonons is studied in a gallium nitride quantum-well—a promising pathway for terahertz (THz) oscillations. The optimal conditions for the LO-phonon-terminated streaming depend, among others, on the density of the electron gas, the low-field electron mobility, the lattice temperature, and the electric field in a very specific way. The present manuscript exploited the electron noise temperature measured at an X band frequency as a marker for the oscillations at THz frequencies. The idea was tested on a deterministic model for a GaN two-dimensional electron gas (2DEG) through calculation of the electron noise temperature spectra in the Langevin approach for the frequency range from 1 GHz to 10 THz. The noise temperature at 10 GHz was found to be in a strong anticorrelation with the THz peaks in the noise temperature spectrum. In particular, a weaker dependence on the applied electric field at 10 GHz implies stronger THz oscillations. In an experiment, the microwave hot-electron noise measurements were carried out for AlGaN/AlN/GaN heterostructures with the 2DEG channel at 10 GHz under pulsed electric field conditions in order to mitigate the effect of Joule heating of the channel. The plateau-like behavior of the noise temperature, in its dependence on the electric field, was obtained for the 2DEG channels with rather low electron densities (2.5×1012 cm−2) in a good agreement with the model. The aforementioned plateau in the electron noise temperature observed at 10 GHz can be used as an indicator for the THz oscillations.