Intersubband Raman gain in strained zincblende III-nitride-based step asymmetric quantum wells: non-parabolicity effects

The conduction band states in step-like strained zincblende nitride-based quantum wells are theoretically investigated including effects of band non-parabolicity. In particular, the intersubband Raman gain is calculated in order to identify the possible use of this kind of structures as sources of THz Raman lasing. The theoretical procedure includes the use of the envelope function approximation, taking into account strain effects on the conduction band offset and position-dependent non-parabolic effective masses. Three-level Raman gain is reported for a group of possible intersubband transitions. The results are discussed in terms of the variation of the geometry of the heterostructure as well as the concentration of In in the well regions. It is shown that under a suitable geometric design and plausible detuning conditions it is possible to achieve–for certain intersubband transitions–values of the intersubband Raman gain above 1000cm-1, quite larger than those previously reported in GaAs- and wurtzite GaN-based double asymmetric quantum wells. Besides, it is found that the band-nonparabolicity acts as a significant element that reduces the Raman gain response in this kind of systems, whereas strain affects it in the same way but the changes are mainly noticed for higher In contents. It turns out that it is necessary to take both effects into account for the better quantitative description on intersubband Raman response in zincblende nitride heterostructures.