Cathodoluminescence mapping of epitaxial lateral overgrowth in gallium nitride

The dislocation arrangements in gallium nitride (GaN) films prepared by lat eral epitaxial overgrowth (LEO) have been studied by cathodoluminescence ma pping and transmission electron microscopy. A very low density of electrica lly active defects (<10(-6) cm(-2)) in the laterally overgrown material is observed. Individual electrically active defects have been observed that pr opagate laterally from the line of stripe coalescence into the overgrown ma terial. Additionally, by mapping wavelength-resolved luminescence in an InG aN quantum well grown on top of the overgrown material, these defects are s hown to be limited to the underlying material and do not propagate normal t o the surface, as in other GaN films. In the seed region, threading disloca tion image widths are seen to be nearly identical in the quantum well and t he underlying GaN, indicating a comparable upper limit (similar to 200 nm) for minority carrier diffusion length in InGaN and GaN. Additionally, it is shown that, through processing variation, these lateral defects can be avo ided in LEO films and that wavelength-resolved cathodoluminescence is an ex cellent large-area method for rapidly and quantitatively observing variatio ns in process development. (C) 1999 American Institute of Physics. [S0003-6 951(99)04813-5].