The Impact of Band Bending on the Thermal Behaviour of Gain in Type-II GaAs-Based “W”-Lasers

We undertake a comprehensive investigation of the temperature (T) and injection dependence of the modal gain in 1240 nm-emitting Type-II (GaIn)As/Ga(AsSb)/(GaIn)As “W” laser active regions for 25<inline-formula><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula>T<inline-formula><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula>300 K. From direct measurements of the short-wavelength transparency point, which serves as a proxy for population inversion, the behaviour of the maximum gain and peak blueshift are used to highlight the different temperature dependencies of the gain at different injection regimes. We show that the thermal redshift of the peak gain at room temperature reduces from 0.53<inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>0.03 nm/<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula>C under flat band conditions to 0.32<inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>0.03 nm/<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula>C at threshold. These results demonstrate the significant role of injection-dependent electrostatic effects and how it may be used through design to tailor the thermal properties of semiconductor lasers employing Type-II “W” active regions.