Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

F. M. Hsiao, M. Schnedler, V. Portz, Y. C. Huang, B. C. Huang, M. C. Shih, C. W. Chang, L. W. Tu, H. Eisele, R. E. Dunin-Borkowski, Ph Ebert, Y. P. Chiu

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Abstract

We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

Original languageEnglish
Article number015701
JournalJournal of Applied Physics
Volume121
Issue number1
DOIs
Publication statusPublished - 2017 Jan 7

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ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Hsiao, F. M., Schnedler, M., Portz, V., Huang, Y. C., Huang, B. C., Shih, M. C., Chang, C. W., Tu, L. W., Eisele, H., Dunin-Borkowski, R. E., Ebert, P., & Chiu, Y. P. (2017). Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy. Journal of Applied Physics, 121(1), [015701]. https://doi.org/10.1063/1.4972563