We present a two-quantum well THz intersubband laser operating up to 192 K. The structure has been optimized with a non-equilibrium Greens 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.
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