Suppressed absolute negative conductance and generation of high-frequency radiation in semiconductor superlattices

We show that space-charge instabilities (electric field domains) in semiconductor superlattices are the attribute of absolute negative conductance induced by small constant and large alternating electric fields. We propose the efficient method for suppression of this destructive phenomenon in order to obtain a generation at microwave and THz frequencies in devices operating at room temperature. We theoretically proved that an unbiased superlattice with a moderate doping subjected to a microwave pump field provides a strong gain at third, fifth, seventh, etc. harmonics of the pump frequency in the conditions of suppressed domains.Comment: 8 pages. Development of cond-mat/0503216 . Version 2: Final version, erratum is include

Superlattice with hot electron injection: an approach to a Bloch oscillator

A semiconductor superlattice with hot electron injection into the miniband is considered. The injection changes the stationary distribution function and results in a qualitative change of the frequency behaviour of the differential conductivity. In the regime with Bloch oscillating electrons and injection into the upper part of the miniband the region of negative differential conductivity is shifted from low frequencies to higher frequencies. We find that the dc differential conductivity can be made positive and thus the domain instability can be suppressed. At the same time the high-frequency differential conductivity is negative above the Bloch frequency. This opens a new way to make a Bloch oscillator operating at THz frequencies.Comment: RevTeX, 8 pages, 2 figures, to be published in Phys. Rev. B, 15 Januar 200

Bloch gain for terahertz radiation in semiconductor superlattices of different miniband widths mediated by acoustic and optical phonons

We report a study of the role of electron scattering at acoustic and polar optic phonons for Bloch gain of a terahertz radiation in semiconductor superlattices of different miniband widths. A three-dimensional Monte Carlo method was employed to calculate the dynamic mobility of miniband electrons in GaAs/AlAs superlattices subject to both static and high-frequency fields at low temperature (4 K); Bloch gain is indicated by a negative real part of the dynamic mobility. We found that for a superlattice with a miniband width smaller than the optic phonon energy (36 meV), scattering of electrons at acoustic phonons alone mediates the formation of electron bunches in momentum space and introduces gain, while for larger miniband widths, optic phonon scattering is dominant for gain. Due to a decrease of the energy-relaxation time of the miniband electrons, the alteration of the superlattice miniband width from smaller to larger magnitude, with respect to the optic phonon energy, results in broadening of the resonancelike dynamic mobility curve and considerable extension of the frequency range for the strong Bloch gain. The study delivers criteria for the observation of the Bloch gain