Differential gain and damping factor in strained InGaAs/GaAs quantum well lasers

The differential gain, modulation response, and damping rate of strained-layer Ino•3Ga(J•7As multiple quantum well (MQW) short cavity graded-index separate confmement heterostrucutre (GRINSCH) and SCH lasers fabricated by chemically-assisted ion beam etching (CAIBE) are analyzed. Calculated differential gains vary from 0.7 to. 1 .6 x 1015 cm2, with only relatively long lasers of 400 p.m demonstrating very high differential gain. For the GRINSCH lasers, a CW 3-dB bandwidth of 22 GHz has been measured that is limited primarily by heating and a low frequency rolloff. The latter is improved dramatically using an SCH design resulting in an improvement of the 3-dB bandwidth to 28 GHz. Cather transport theory (also known as well-barrier hole burning) is shown to model the damping behavior of quantum well lasers from low to moderate photon densities.