Gain and loss as a function of current density and temperature in interband cascade lasers

We characterize the internal efficiency, internal loss, and optical gain versus current density in 7-stage interband cascade lasers operating at λ=3.1 and 3.45 μm using a cavity-length study of the external differential quantum efficiency (EDQE) and threshold current density at temperatures between 300 and 345 K. We find that the pronounced efficiency droop of the EDQE at high current densities is primarily due to an increase in the internal loss rather than a reduction in the internal efficiency. On the other hand, if the current density J is fixed, the temperature variation of the EDQE at that J is due primarily to a decrease of the internal efficiency. The gain versus current density is fit well by a logarithmic relationship, although the magnitude of the experimental gain is >20% below the theoretical estimate.