Optical gain and spontaneous emission in InGaAs/GaAs multiple quantum well laser diodes

We present gain and spontaneous emission measurements in In(0,35)Ga(0,65)As/GaAs multiple quantum well lasers. First, the gain is extracted from measured amplified spontaneous emission through a laser facet. Second, unamplified spontaneous emission is detected through the transparent GaAs-substrate. Taking advantage of the fundamental relationship between gain and spontaneous emission, the separation of the electron and hole quasi-Fermi levels, Delta E(ind F), at various bias currents below laser threshold is accurately determined. Theoretically, Delta E(ind F) is calculated utilizing a simple two-subband structure model. Fitting the theoretical predictions to the experimental data allows us to determine the threshold carrier density (n(ind th) = 2.O X 10(exp 18) cm(exp-3)), the in-plane hole effective mass (m(ind v1) = 0.21(ind m(ind o))), and the amount of band gap shrinkage at threshold (Delta E(ind g,th) = 33 meV)).