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Deep-UV photoemission electron microscopy for imaging nanoscale heterogeneity and defects in gallium nitride



Andrew Winchester, Michael Mastro, Travis Anderson, Jennifer Hite, Andrei Kolmakov, Sujitra Pookpanratana


Gallium nitride (GaN) is a promising wide-bandgap material for high-power electronics, where GaN-on-GaN homoepitaxy is being developed for fabrication of compact high-voltage vertical devices. However, GaN substrate quality is variable and strongly influences the properties of epitaxial layers grown on top which in turn affects device performance and reliability. Hence, better knowledge of the surface electronic properties is needed, in particular after wafer processing steps, which can introduce surface contamination and oxide layers. Photoemission-based techniques provide chemical and electronic information but are surface-sensitive; therefore, the formation of native oxides or contamination from ambient conditions can affect findings. Here, we present the initial results of various surface preparation methods on the electronic properties of p-type GaN epitaxial layers grown via metal-organic chemical vapor deposition (MOCVD) in preparation for photoemission electron spectroscopy and microscopy characterization. We use X-ray photoelectron spectroscopy (XPS) to evaluate changes in residual contamination after treatment. We find that piranha-based cleaning methods have large reductions in surface carbon contamination, while NH4OH and HCl-based treatments remove surface oxide. The elemental core levels and valence band correspondingly exhibit rigid binding energy shifts with the different treatment methods, indicating reduced surface band-bending. Both XPS and initial photoemission electron microscopy results of the photoelectron yield corroborate with the deeper valence band with respect to Fermi energy measured for the plasma-cleaned sample. These results demonstrate that combined ex-situ treatments for carbon and oxygen removal are more effective, yet further in-situ cleaning is necessary for more complete contamination removal.
Proceedings Title
SPIE Proceedings Volume 12421, Gallium Nitride Materials and Devices XVIII
Conference Dates
January 28-February 2, 2023
Conference Location
San Francisco, CA, US
Conference Title
SPIE Photonics West


gallium nitride, GaN on GaN, pn GaN, surface cleaning, photoelectron spectroscopy, photoemission electron microscopy


Winchester, A. , Mastro, M. , Anderson, T. , Hite, J. , Kolmakov, A. and Pookpanratana, S. (2023), Deep-UV photoemission electron microscopy for imaging nanoscale heterogeneity and defects in gallium nitride, SPIE Proceedings Volume 12421, Gallium Nitride Materials and Devices XVIII, San Francisco, CA, US, [online],, (Accessed June 22, 2024)


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Created March 15, 2023, Updated March 27, 2023