The authors present a study on the effects of design parameters on the performance of terahertz quantum-cascade lasers by using a Monte Carlo method, including essential scattering mechanisms and the hot-phonon effect. Three design parameters, i.e. injection and extraction barrier widths and doping concentration, are investigated. In the range of the three design parameters we used, simulated results show that the current density increases monotonically with the decrease of barrier widths and the increase of doping concentration. The calculated gain is more sensitively dependent on the injection barrier width and doping concentration. Thicker extraction barriers, i.e. from 39 to 48 Å, are acceptable.

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We report the electrical and the optical characteristics of 2 THz quantum-cascade lasers with a similar four-well resonant-phonon design. A Monte Carlo simulation, employed to evaluate the temperature performance of the device, indicates that the degradation of material gain with increasing temperature is attributed to the rapid decrease in the lifetime of the upper lasing level and the relatively stable lifetime of the lower lasing level. Because of the broadening effect of the temperature dependent gain profile, our calculations overestimate the peak gain and subsequently overrate the maximum operating temperature. Under a linear approximation condition, the deduced maximum operating temperature is in good agreement with experiment. Both experiment and simulation show that the lasing frequency is insensitive to temperature.

We have performed current-voltage (I-V) measurements on a terahertz quantum-well photodetector (QWP) at different temperatures and employed an emission-capture model to simulate the I-V curves. A temperature-dependent vertical electron drift mobility has been used to fit the curves from 7 K to 20 K. Photocurrents caused by 300 K background radiation have also been measured at different temperatures and a background-limited infrared performance (blip) temperature of 12 K for this terahertz detector has been determined. The current-temperature (I-T) curves derived from the measured dark I-V curves indicate that the thermionic emission process is the major mechanism for dark current in this terahertz detector.