Gain and radiative current density in InGaAs/lnGaAsP lasers with electrostatically confined electron states

We have calculated the gain and radiative current density as a function of carrier density in a quantum well system which includes the effects of electrostatically confined electron states. We consider a model InGaAs/InGaAsP/InP laser structure and investigate how the lasing characteristics change as the conduction band line-up moves from being type I to type II. We find for modest type II offsets (up to ≈50 meV) and a typical well width of 100 Å that the transparency carrier densities are larger than comparable type I structures, and that the differential gain degrades only gradually. We also calculate the 2-D carrier density at transparency and threshold and the radiative component of the current density for InGaAs/InGaAsP lasers with both compressive and tensile strained quantum wells emitting around 1.5 μm. We find that the mechanisms by which threshold current is reduced are different in tensile and compressive laser structures. We see that the radiative current decreases with increasing tension even in the situation where the conduction band offset is expected to be type II, with only a modest increase in 2-D carrier density. This suggests that the total threshold current density of these lasers should decrease in the type II region, in contradiction to the available experimental data