Recombination, gain, band structure, efficiency, and reliability of 1.5-μm GaInNAsSb/GaAs lasers

We present temperature-dependent measurements of the local Z parameter, which reflects the dominant recombination processes. At room temperature, Z increases with current from 1.2 at low bias up to a threshold value, Zth, of only 2.0, demonstrating the existence of significant amounts of monomolecular recombination. At elevated temperatures, Zth rises above 2.5. We calculate the laser's band diagram and estimate 35 meV of band-gap renormalization at threshold through polarization-resolved measurements of exciton peaks in the absorption spectrum and inflection points of the absorption, spontaneous emission, and gain spectra. The small effective valence-band barrier height of 115 meV leads to hole leakage due to thermionic emission and carrier spillover into the barriers. This could explain the increase in Zth at elevated temperatures and decrease in internal quantum efficiency from 57% at 15°C to 47% at 75°C. We also analyze the spontaneous emission and gain spectra below and above threshold. The spontaneous emission clamped rather weakly at threshold, which also partially explains the low internal efficiency at room temperature. We present initial reliability measurements of over 100 h at 10-mW continuous-wave power from a single facet. After 50 h of life testing, the threshold current increased by 79% and the external differential quantum efficiency decreased by 39% of their respective pretest values. By comparing the local Z parameter versus current-density curves before and after life testing, we have identified an increase in monomolecular recombination as the main source of degraded device performance.