High-Resolution Cathodoluminescence Mapping for Doping Quantification across a Wide Range of Silicon Concentrations in GaN Epitaxial Layers.

Abstract

This study demonstrates cathodoluminescence (CL) mapping as a quantitative nanoscale method for analyzing silicon doping in GaN epitaxial layers. By correlating near-band-edge energy shifts and line-width broadening with the doping concentration, local carrier densities from unintentionally doped GaN to 5 × 10¹⁸ cm^-3 are mapped with nanoscale resolution, including in quasi-vertical PN diodes. Drift-diffusion simulations show that carrier diffusion does not limit spatial resolution, with radiative recombination confined within ∼100-150 nm. Calibration against secondary ion mass spectrometry validates the quantitative accuracy of the approach. We show that the peak energy is sensitive to both doping and strain, whereas the line width provides a more robust indicator of doping than the peak energy due to its reduced sensitivity to strain, with increased uncertainty below ∼10¹⁷ cm^-3. This method enables simultaneous mapping of doping and strain, offering a powerful tool for the optimization of GaN-based power devices.