Cathodoluminescence mapping of epitaxial lateral overgrowth in gallium nitride

Abstract

The dislocation arrangements in gallium nitride (GaN) films prepared by lateral epitaxial overgrowth (LEO) have been studied by cathodoluminescence mapping and transmission electron microscopy. A very low density of electrically active defects ${\text{(<10}}^{\text{−6}} {\mathrm{cm}}^{\mathrm{-2}})$ in the laterally overgrown material is observed. Individual electrically active defects have been observed that propagate laterally from the line of stripe coalescence into the overgrown material. Additionally, by mapping wavelength-resolved luminescence in an InGaN quantum well grown on top of the overgrown material, these defects are shown to be limited to the underlying material and do not propagate normal to the surface, as in other GaN films. In the seed region, threading dislocation image widths are seen to be nearly identical in the quantum well and the underlying GaN, indicating a comparable upper limit (∼200 nm) for minority carrier diffusion length in InGaN and GaN. Additionally, it is shown that, through processing variation, these lateral defects can be avoided in LEO films and that wavelength-resolved cathodoluminescence is an excellent large-area method for rapidly and quantitatively observing variations in process development.