Non-equilibrium electron heating in inter-subband terahertz lasers.

P. Kinsler, R. W. Kelsall, P. Harrison.

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

    J. Appl. Phys. 91, 904 (2002).

Inter-subband laser performance can be critically dependent on the
nature of the electron distributions in each subband.  In these first
Monte Carlo device simulations of optically pumped inter-subband THz
lasers, we can see that there are two main causes of electron heating:
inter-subband decay processes, and inter-subband energy transfer from
the {\lq\lq}hot{\rq\rq} non-equilibrium tails of lower subbands.  These
processes mean that devices relying on low electron temperatures are
disrupted by electron heating, to the extent that slightly populated
subbands can have average energies far in excess of the that of either
the lattice or other subbands.  However, although these heating effects
invalidate designs relying on low temperature electron distributions,
we see that population inversion is still possible in the high-THz
range at 77K in both stepped and triple-well structures; and that our
11.7THz triple-well structure even promises inversion at 300K.

Email: Dr.Paul.Kinsler@physics.org