Evaluating the Local Bandgap Across in_xGa_1-xas Multiple Quantum Wells in a Metamorphic Laser via Low-Loss EELS

Using high-resolution scanning transmission electron microscopy and low-loss electron energy loss spectroscopy, the local bandgap (E_g), indium concentration, and strain distribution across multiple In_xGa_1-xAs quantum wells (QWs), on a GaAs substrate, within a metamorphic laser structure are correlated. The findings reveal significant inhomogeneities, particularly near the interfaces, for both the indium and strain distribution, and subtle variations in the E_g across individual QWs. The interplay between strain, composition, and E_g is further explored by density functional theory simulations, indicating that variations in the E_g are predominantly influenced by the indium concentration, with strain playing a minor role. The observed local inhomogeneities suggest that differences between individual QWs may affect the collective emission and performance of the final device. This study highlights the importance of spatially resolved analysis in understanding and optimizing the electronic and optical properties for designing next-generation metamorphic lasers with multiple QWs as the active region.