  We present a two-quantum well THz intersubband laser operating up to 192 K.
The structure has been optimized with a non-equilibrium Green's function model.
The result of this optimization was confirmed experimentally by growing,
processing and measuring a number of proposed designs. At high temperature
(T>200 K), the simulations indicate that lasing fails due to a combination of
electron-electron scattering, thermal backfilling, and, most importantly,
re-absorption coming from broadened states.
