The carrier dynamical issues for extending the 
    operating wavelength of quantum cascade lasers

    P. Harrison, K. Donovan, R. W. Kelsall, and P. Kinsler,

    Institute of Microwaves and Photonics, 
    School of Electronic and Electrical Engineering, 
    University of Leeds, 
    Leeds LS2 9JT,
    United Kingdom.

    SPIE Proceedings Vol.  3828, 17-23 (1999).

    Electron-longitudinal optic phonon and
       electron-electron intersubband scattering rates are
       calculated for a variety of quantum well systems. It is
       demonstrated that the internal quantum efficiency of a
       Terahertz radiative intersubband transition can be
       greater than in the mid-IR at 4K, however by room
       temperature has fallen to around 20 percent. A study of
       the internal quantum efficiency of a Terahertz energy
       intersubband transition in double and single quantum
       wells, has shown that the vertical intrawell transition
       is more efficient than the diagonal interwell
       transition. 

Email: Dr.Paul.Kinsler@physics.org