Theory of gain spectra for quantum cascade lasers and temperature dependence of their characteristics at low and moderate carrier concentrations

摘要

We have developed a theory describing the operation of lasers bsed on intersubband transitions in a quantum well. The theory combines a first-principles description of the intersubband lineshape and the optical gain with kinetic models for carrier heating. The theory is consistent with the experimental data available and suggest new ways of improving the laser design for room temperature operation with high ouput power. At low carier concentrations, it is possible to achieve positive values of the gain at room temperature even in the absence of an overall population inersion between quantum well subbands. For higher (but still moderate) concentrations, the theory predicts a peculiar dependence of the output wavelength on the pump current, including a regime where the asing wavelength switches "digitally" between two stable values.