# Determination of the carrier diffusion length in GaN from cathodoluminescence maps around threading dislocations: fallacies and opportunities

## TL;DR

This study combines theoretical and experimental approaches to analyze exciton behavior around threading dislocations in GaN, revealing that cathodoluminescence energy contrast, not intensity, can be used to determine exciton diffusion length.

## Contribution

It demonstrates that cathodoluminescence intensity contrast is not suitable for measuring diffusion length, but energy contrast provides a reliable method for its determination in GaN.

## Key findings

- Cathodoluminescence intensity contrast is weakly affected by exciton diffusion.
- Energy contrast in cathodoluminescence maps depends on exciton diffusion length.
- Dark spot size around dislocations does not indicate exciton diffusion length.

## Abstract

We investigate, both theoretically and experimentally, the drift, diffusion, and recombination of excitons in the strain field of an edge threading dislocation intersecting the GaN{0001} surface. We calculate and measure hyperspectral cathodoluminescence maps around the dislocation outcrop for temperatures between 10 to 200 K. Contrary to common belief, the cathodoluminescence intensity contrast is only weakly affected by exciton diffusion, but is caused primarily by exciton dissociation in the piezoelectric field at the dislocation outcrop. Hence, the extension of the dark spots around dislocations in the luminescence maps cannot be used to determine the exciton diffusion length. However, the cathodoluminescence energy contrast, reflecting the local bandgap variation in the dislocation strain field, does sensitively depend on the exciton diffusion length and hence enables its experimental determination.