Intersubband quantum-box semiconductor lasers

It is shown that semiconductor lasers utilizing intersubband transitions in quantum boxes, so-called intersubband quantum-box (IQB) lasers, can have significantly lower threshold current densities and operating voltages than quantum cascade (QC) lasers. In order to achieve this result, an enhancement factor of about 20 in the LO-phonon-assisted electron relaxation time is necessary. The increased gain for the radiative stage in an IQB laser eliminates the need for a multiradiative-stage structure (typically 25 stages in QC lasers). In turn, the electron injector and Bragg mirror regions on either side of the active region can be separately optimized. Due to their inherently lower input power requirements, IQB lasers operating in the mid-IR wavelength range should be capable of higher average-output powers than QC lasers at all temperatures. Furthermore, continuous-wave (CW) operation at room temperature with high wallplug efficiency becomes possible.