Strain mapping of GaN substrates and epitaxial layers used for power electronic devices by synchrotron X-ray rocking curve topography

Strain and tilt maps of gallium nitride (GaN) materials including substrates, ion-implanted and annealed epilayers, and etched and regrown epilayers by different etching methods have been generated from synchrotron X-ray rocking curve topography. The strain map of the ammonothermal grown GaN substrate shows uniform low strain values, while that of the patterned hydride vapor phase epitaxy (HVPE) grown substrate shows high strain centers as well as uniformly distributed low strain between them. Strain variations within the as-implanted wafers and the annealed wafers are similar, while the tilt levels are significantly decreased for the annealed wafers. The inductively coupled plasma (ICP) etched and then regrown sample gives rise to the significant variations in strain values within the imaged region, while using tertiary butyl chloride (TBCl) to etch the sample does not affect the strain distribution compared to the continuously grown sample without etching and can remove some damage from a preceding ICP etching process.