Spatially resolved photoluminescence and Raman spectroscopy of bandgap gratings fabricated in GaAs/AlAs superlattice waveguide using quantum well intermixing

Photoluminescence (PL) and Raman spectroscopy were devised to study bandgap gratings fabricated in a waveguide with a core consisting of GaAs/AlAs short superlattice (SSL) structure using quantum well intermixing (QWI). The spatially resolved PL is carried out on the superlattice layer from the sample surface, as well as from a cleaved facet to the side of the epitaxial layer. The PL from the sample surface showed a modulation in the PL wavelength with shoulders being observed. The root cause of this observation was resolved via PL scans of the cleaved side of the grating. The results were further supplemented via Raman spectroscopy measurements, where Raman spectra were collected at different depths of the SSL through probing the SSL layer cross-section. SSL-related phonon states were clearly observed for the lower part of the SSL layer where intermixing did not take place, while the Raman spectra for the intermixed regions showed regular bulk phonon modes, indicating the SSL layer intermixing.