MODULATION BANDWIDTH PREDICTIONS FOR INTER-SUBBAND QUANTUM WELL SEMICONDUCTOR LASERS

Intersubband semiconductor lasers offer opportunities for obtaining compact laser sources with emission wavelengths in the mid-infra-red to far-infra-red range (say 5 µm -100 µm). Such lasers utilise electronic transitions between conduction band subbands in coupled quantum well structures to achieve population inversion and lasing. Intersubband lasers based upon hole transitions in valence band subbands may also be contemplated .Since only one charge carrier species is involved in the lasing process the devices are also termed unipolar semiconductor lasers . Unipolar intersubband semiconductor lasers have recently attracted considerable attention following the report by Faist, Capasso et al of Mid-Infra-Red (MIR) light emission and lasing action in so-called Quantum Cascade lasers [1].That work gave the first practical demonstration of a long-standing proposals for the utilisation of intersubband transitions to obtain lasing action in semiconductor superlattices [2].Quite considerable progress has been made in improving the operating characteristics of those devices [3,4]. In these circumstances it becomes relevant to assess the expected performance characteristics of intersubband laser devices such as their anticipated direct current modulation capabilities. That is the aim of the present contribution.