Intersubband quantum-box semiconductor lasers

It is shown that semiconductor lasers utilizing intersubband transitions in quantum boxes, so-called intersubband quantum-hox (IQB) lasers,can have si gnificantly lower threshold current densities and operating voltages than q uantum cascade (QC) lasers, Tn order to achieve this result, an enhancement factor of about 20 in the LO-phonon-assisted electron relaxation time is n ecessary. The increased gain for the radiative stage in an IQB laser elimin ates the need for a multiradiative-stage structure (typically 25 stages in QC lasers), In turn, the electron injector and Bragg mirror regions on eith er side of the active region can be separately optimized. Due to their inhe rently lower input power requirements, IQB lasers operating in the mid-TR w avelength range should be capable of higher average-output powers than QC l asers at all temperatures. Furthermore, continuous-wave (CW) operation at r oom temperature with high wallplug efficiency becomes possible.