Investigation of Defect States in Polycrystalline GaN Grown on Si(111) Using Sub-Bandgap Laser-Excited Scanning Tunneling Spectroscopy
F.-M. Hsiao1,2,3*, M. Schnedler2, V. Portz2, Y.-C. Huang4, B.-C. Huang5, M.-C. Shih1, C.-W. Chang1, L.-W. Tu1, H. Eisele6, R. E. Dunin-Borkowski2, Ph. Ebert2, Y.-P. Chiu1,3,5
1Department of Physics, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
2Peter Grünberg Institut, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
3Department of Physics, National Taiwan University, Taipei, 10617, Taiwan
4Department of Physics, National Cheng Kung University, Tainan, 70101, Taiwan
5Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
6Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany
* presenting author:FEI-MAN HSIAO,
The photo-induced charge carriers in GaN films were shown to strongly depend on the defect states. In this work, sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy demonstrate the great potential to obtain photo-induced electronic properties at defect-rich GaN films under the illumination condition. A dramatic increase in the tunneling current at positive sample voltages is observed in the defect-rich GaN layers under light illumination, resulting from the excitation of charge carriers at defect states. Sub-bandgap laser-excited scanning tunneling spectroscopy enables us to directly characterize the excitation of charge carriers at defect states and demonstrate photo-induced carrier behavior in conduction band in GaN films.

Keywords: X-STM, LM-STM, GaN