Investigation of MIR-pumped quantum-cascade structures as emitters of THz radiation

Kurzfassung

One proposal to obtain THz radiation from a compact semiconductor source at room temperatures is based on an optically pumped, electrically driven (OPED) quantum-cascade structure. It has been theoretically shown that such a structure may allow for overcoming the fundamental Manley-Rowe limit of frequency conversion by recycling the pump photons. Furthermore, quantum coherence effects and gain without inversion have been predicted. However, the realization of such a structure has proven to be difficult, which is due to nonlinear transport effects such as the formation of electric-field domains. We investigate the influence of MIR pumping on the electrical transport properties in different OPED quantum-cascade structure. Experiments are performed using free-electron laser (FEL) radiation in the range of 10 to 12 μm. Although the effect of the FEL pumping on the transport properties is rather small and ambiguous, in particular with respect to different polarization directions, a small emission signal in the THz range is observed. Additional experiments with a pulsed CO2 laser show a clear influence of the pumping being on or off and of its polarization direction on the dc current-voltage characteristics.