TE AND TM OPTICAL GAINS IN ALGAAS GAAS SINGLE-QUANTUM-WELL LASERS

TE and TM optical gains were measured in AlGaAs/GaAs single-quantum-well (SQW) diode lasers at 300 K. Both the TE and TM gain spectra were step-like. The long and short wavelength steps in the experimental spectra were attributed to the onset of transitions from the first (e1) and second (e2) electronic subbands respectively. With increasing pumping current, the growth of the gain amplitude in the e1 transition slows down, the peak gain being approximately the same for TE and TM polarizations. On the contrary, the TE gain dominates over the TM gain in the e2 transition, which shows up at higher injection. Most of the polarization features of the observed gain spectra are easily interpreted within a model of direct optical transitions with the band mixing, relaxation broadening and bandgap shrinkage effects taken into account. At the same time, the gain saturation in the e1 transition observed in experiment can hardly be explained by the theory.