Monte Carlo modelling of far-infrared intersubband lasers

An ensemble Monte Carlo simulation method has been used to model the carrier dynamics of optically pumped intersubband lasers. GaAs/AlGaAs asymmetric (single step) and triple quantum well structures are studied: both are 4-subband systems designed for intersubband pumping by a View the MathML source laser, and for far-infrared emission at 11.7 THz (View the MathML source). The simulations predict population inversion at 77 K for the asymmetric quantum well, but not at 300 K, whence intersubband electron–electron interactions cause significant re-distribution of electron kinetic energies in the 4th subband. However, simulations of the triple quantum well structure show strong inversion at 77 K, and marginal inversion at 300 K. The improved performance of the triple quantum structure in this case is attributed to stronger 3rd–2nd subband scattering (which depopulates the lower of the two laser levels) due to an anticrossing of eigenstates, and to reduced energy re-distribution effects.