Influence of substrate misorientation on the emission and waveguiding properties of a blue (In,Al,Ga)N laser-like structure studied by synchrotron radiation microbeam X-ray diffraction

In this work, we study how an epitaxial laser-like (or superluminescent diode-like) structure is modified by intentional changes of the substrate misorientation in the range of 0.5°–2.6°. The 40 μm × 40 μm test structure with misorientation profiling was fabricated using multilevel photolithography and dry-etching. The local structural parameters were measured by synchrotron radiation microbeam X-ray diffraction, with the sampling area of below 1 μm × 1 μm . We directly obtained the relation between the misorientation and indium content in the quantum well, changing from 9% to 18%, with a high resolution (small misorientation step). We also show a good agreement of local photoluminescence emission wavelength with simulation of transition energy based on synchrotron radiation microbeam X-ray diffraction (SR-XRD) data and estimated Stokes shift. We observe that the substrate misorientation influences also the InGaN waveguide and AlGaN cladding composition. Still, we showed through simulation of the optical confinement factor of a full laser diode structure that good light guiding properties should be preserved in the whole misorientation range studied here. This proves the usefulness of misorientation modification in applications like broadband superluminescent diodes or multicolor laser arrays.