Gain Measurements in InGaAs/InGaAsP Multiquantum-Well Broad-Area Lasers

The paper describes gain measurements in InGaAs/InGaAsP multiquantum-well lasers at 1.55-mu-m derived from the spontaneous emission under current injection. The gain spectrum in a broad-area laser device is determined from the spontaneous emission spectrum on using the measured differential quantum efficiency and the loss conditions at the lasing wavelength at threshold. Spectral measurements from 1.0 to 1.7-mu-m with intensity resolution over four orders of magnitude clearly exhibit contributions from the barriers, and indicate that a nonthermal equilibrium may exist between the well and barrier materials. Band-filling effects in the well can be seen in the absorption spectra for low injection currents. Gain spectra are obtained for carrier injection levels from 1% of threshold to 1.5 times threshold.