Influence of growth temperature on carrier recombination in GaInNAs-based lasers

Relatively small changes in growth parameters, such as the active layer growth temperature, have been shown to have dramatic effects on the threshold current density J_th for GaInNAs-based lasers. The authors consider the influence of the growth temperature on the contribution of the defect-related current to J_th in structures with nominally identical quantum wells. The two sets of devices used in this study are 1.27-μm GaInNAs SQW edge-emitting lasers which are nominally identical except that the active regions were grown at 422°C and 456°C. At room temperature it was found that J_th for the high growth temperature lasers (∼330 A/cm²) is reduced by a factor of ∼2.8 when compared to J_th of the low growth temperature devices (∼970 A/cm²). To determine the processes responsible for this change the light emitted from a window in the substrate contact of the devices was measured as a function of current and temperature, which yields the absolute magnitudes of the defect-, radiative- and Auger-related recombination processes at threshold. The results show that the strong increase in J_th with changing growth conditions can be explained almost entirely by an increase in the monomolecular recombination coefficient A, yielding a larger defect-related current contribution. Furthermore, the extracted radiative- and Auger-related current paths in the two devices are of very similar magnitude. This is strong evidence that the change in growth conditions does not affect the internal losses of the devices, as the threshold carrier density n_th appears not to have changed significantly. By increasing the number of wells to three, J_th per well of the high growth temperature devices could be further reduced (∼190 A/cm²) at room temperature. The results suggest that increasing the number of wells not only decreases the carrier density at threshold but additionally reduces the average defect-related current density in these devices.