Terahertz generation in nitrides due to transit-time resonance assisted by optical phonon emission.

The conditions for THz radiation generation caused by electron transit-time resonance in momentum and real spaces under optical phonon emission are analyzed for nitride-based materials and their structures. It is shown that such a mechanism provides a unique possibility to realize sub-THz and THz radiation generation at the border between the electro-optical and electronic techniques by using two alternative approaches: (i) amplification of transverse electromagnetic waves in 3D bulk materials and 2D quantum wells, and (ii) longitudinal current-field instabilities in sub-micron and micron n(+)nn(+) diodes. Estimations of frequency regions, output power and efficiency of the generation demonstrate that nitrides are promising materials for THz radiation generation.

Microwave-induced transient parametric gratings.

We propose a new method for the formation of light-induced transient gratings in microwave-biased semiconductor crystals that exhibit a negative differential resistivity. Nonuniform heating of the electron gas in alternating electric fields induces spatially periodic modulation of the refractive index with spacing that is tunable by the external field frequency. Numerical simulations performed on a bulk GaAs sample prove that transient parametric gratings of both free-carrier and electro-optic origin can be triggered by a spatially modulated light pattern or by uniform photoexcitation.