In this work we report on two novel types of high-frequency driven semiconductor superlattice oscillators, suitable for generation of subterahertz and terahertz (THz) radiation. The oscillators are based on high-frequency driven miniband transport. For the first of the two oscillators, we present experimental and theoretical results and for the second oscillator a theoretical treatment; this oscillator has not yet been realised experimentally.
The second oscillator we present, the double resonance superlattice parametric oscillator, is for up conversion of radiation. It oscillates simultaneously at the third and fifth harmonic of a pump frequency. We could demonstrate experimentally double resonance oscillations in a GaAs/AlAs superlattice pumped at 100 GHz. The superlattice was mounted in a waveguide structure that served as resonator for both harmonics. Double resonance oscillations were indicated by a threshold behaviour of the third and fifth harmonic. We found that oscillations at the fifth harmonic did occur only together with oscillations at the third harmonic. On the basis of the double resonance oscillator we built a sub-THz source delivering tunable (~ 10%), monochromatic radiation around 500 GHz (output power ~ 10µW). Used as a frequency multiplier, the superlattice generated radiation at the eleventh harmonic with a frequency of about 1.1 THz.
A theoretical treatment of the double-resonance oscillator, based on a semiclassical theory of the miniband transport, showed that two coupled parametric processes occur and that double-resonance oscillations are in principle possible up to a fifth harmonic frequency of the order of 10 THz.
The second oscillator we propose, the THz-field driven Bloch oscillator, is for down conversion of THz-radiation. It is driven by a THz-field of fixed frequency and can generate radiation in a wide frequency range. Our theoretical treatment shows that the THz-field driven Bloch oscillator can generate radiation within the whole frequency range from almost zero frequency to the pump frequency with a high conversion efficiency (~5-15%). The oscillator is based on a synchronised motion of the miniband electrons under the influence of a THz-pump field. We present superlattice material which is suitable as active element of a THz-field driven Bloch oscillator.