Simple model for carrier spill-over in quantum-well lasers consistent with local charge neutrality

Abstract

For separate confinement heterostructure (SCH) quantum well (QW) lasers, carrier injection levels can be controlled by changing cavity losses. In the low injection case, carriers are confined within the QW, and spill-over into the barrier can be neglected. In the very high injection case, on the other hand, carriers in the barrier are dominant, and the QW contribution becomes insignificant. In the intermediate injection range, carrier distribution in both QW and barrier need to be taken into account. A simplified band filling model is developed for this case, in which charge neutrality condition plays a very important role with the band-offset ratio used as an adjustable parameter. Because of the structural difference between conduction and valence bands, the band offset ratio may be very sensitive to the charge neutrality criterion in both QW and barrier. For a particular SCH InGaAs/GaAs QW device (7.5 nm QW, 250 nm barrier) that we have studied in detail, local charge neutrality forces the conduction band offset ratio, Qc, to change from 0.60 to 0.63, for injection levels (described by total number of carriers) ranging from 0.2 × 1013 to 8.5 × 1013 (cm−2). Gain spectra are calculated based on the model including QW and barrier transitions.