The carrier-induced index change in AlGaAs and 1.3-micron InGaAsP diode lasers

The carrier-induced index change has been measured for a large number of broad-area AlGaAs and 1.3-micron InGaAsP diode lasers. The observed index change with injected carrier density is -(1.2 + or - 0.2) x 10 to the -20th cu cm for AlGaAs lasers and -(2.8 + or - 0.6) x 10 to the -20th cu cm for 1.3-micron lasers. The index change at threshold varies from -0.03 to -0.06 for AlGaAs lasers and from -0.04 to -0.10 for InGaAsP lasers. This variation is correlated with the carrier density at threshold, which depends on active layer thickness and doping level. For the first time, the observed index change is compared to the carrier density found from differential carrier lifetime measurements. This accurate determination of the carrier density represents a significant improvement over previous studies.