Comparison of linewidth enhancement factors in midinfrared active region materials

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Abstract
We report calculations of the linewidth enhancement factor for five midinfrared active region materials. The linewidth enhancement factors for two type-I quantum wells based on InAsSb are 2.5 and 5.4, which represent a reduction of up to a factor of 2.6 with respect to bulk InAs 0.91 Sb 0.09 . However, active region materials based on the type-II, InAs/GaInSb system have linewidth enhancement factors near 1.0, which is a factor of 2–5 reduction compared to the type-I quantum wells. The reduction of the linewidth enhancement factor is associated with both a reduction of the mismatch between the conduction and valence banddensities of states and the presence of conduction band dispersion. We describe an additional optimization that is possible in the type-II materials: Carefully placed intersubband absorption features can be used to further reduce the linewidth enhancement factor. We show that linewidth enhancement values as low as 0.3 can be obtained in the type-II superlattices when fabricated into a distributed feedback structure.