Broadband flat-top gain characteristics based on three-component InGaAs/GaAs asymmetric quantum well

This work investigates the improved spectral performance in asymmetric quantum well (AQW) and demonstrates a triple-component InGaAs/GaAs active region designed for flat, broadband gain. This structure consists of three In_xGa_1-xAs layers with different indium compositions: In_0.17Ga_0.83As (4 nm), In_0.14Ga_0.86As (3 nm), and In_0.10Ga_0.90As (3 nm). COMSOL-based simulations reveal that this configuration forms multiple separated radiative recombination centers, resulting in a stepped energy band profile. This structure effectively extends the quasi-Fermi level spacing by approximately 10% compared to traditional single quantum well structures (at a current density of 7.5 × 10^-6 A/cm²), demonstrating significant potential for spectral broadening. Experimentally, the modal gain was extracted through dual-facet electroluminescence (EL) measurements at room temperature. The results show that the full width at half maximum (FWHM) of the modal gain spectrum broadens significantly with increasing current density, reaching up to 105 nm-3.5 times broader than that of traditional quantum well structures. Moreover, the gain spectrum exhibits a uniform profile over 900-1000 nm, with a gain ripple of only ∼0.49, confirming excellent flat-top characteristics. Both theoretical simulations and experimental results confirm that the proposed asymmetric quantum well structure offers substantial advantages in spectral broadening and uniform output. This study demonstrates the application potential of AQW structure in broadband light sources, such as superluminescent diodes (SLDs) and wide-tunable lasers, depending on the subsequent waveguide design, cavity configuration, and operating conditions.