Influence of conduction-band non-parabolicity on terahertz intersubband Raman gain in GaAs/InGaAs step asymmetric quantum wells

The conduction electron states in step-like strained GaAs/InGaAs quantum wells are theoretically investigated under the effective mass approximation, taking into account the effects of band non-parabolicity. With such information, the intersubband three-level Raman gain is calculated looking to reveal a possible application of the studied systems as sources for THz Raman lasing. A group of high-gain intersubband transitions is identified, and the results are strongly dependent on a suitable geometric design in terms of potential well widths which can lead to values of the Raman gain between 200 and 400cm-1, the latter values being close to those previously reported in GaAs-based double asymmetric quantum wells. Secondary radiation frequencies are identified within the range of few tens of THz. It is found that the influence of band non-parabolicity causes a significant reduction of the Raman gain, in comparison with the values obtained neglecting such a phenomenon. Therefore, conduction-band non-parabolicity becomes a crucial element for the accurate quantitative description of the intersubband-related optical response in low-dimensional heterostructures involving small gap materials.