Optical gain of type II inter-sub-band quantum cascade lasers

We have calculated the optical gain of inter-sub-band quantum cascade lasers based on type II heterostructures such as InAs-GaSb-AlSb, using a model that includes the whole band diagram of the structure as well as the dynamics of all the processes involved. A comparison with similar calculations for conventional type I quantum cascade lasers based on the InGaAs-InAlAs heterostructure shows the theoretical superiority of type II lasers, with an optical gain more than 50% higher than that of type I lasers and a much more efficient energy conversion.