Bipolar THz-lasing structures based on InAs-GaSb coupled quantum wells as an alternative to intersubband lasing.

In spite of rather impressive achievements in intersubband quantum cascade lasers their current parameters are still far from the needs of practical implementation. We compare theoretical prospects of THz gain for two cases: intersubband GaAs-based quantum cascade lasers and interband laser based on coupled quantum wells InAs-GaSb. Our methodology of such a comparison is reduced to following: The most typical design of GaAs-based QCL is compared with an InAs-GaSb coupled quantum well laser operating in the same frequency range. The detailed density matrix based calculation shows that the maximal possible gain for CQWL can be three orders of magnitude higher. We present details on LO-phonon emission rates in typical QCL structures. This calculation supports the statement that low depopulation selectivity might be an essential feature of QCL in few THz spectral range.