IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Electronics Tuesday Sessions
       Session EL-TuP

Paper EL-TuP10
Effects of Surface Band Bending on Electrical Properties of AlGaN/GaN HFET Observed by I-V and XPS Measurements

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Electronic Materials Poster Session
Presenter: K.J. Choi, Pohang University of Science and Technology (POSTECH), Korea
Authors: J.-L. Lee, Pohang University of Science and Technology (POSTECH), Korea
K.J. Choi, Pohang University of Science and Technology (POSTECH), Korea
C.M. Jeon, Pohang University of Science and Technology (POSTECH), Korea
J.H. Lee, Kyungpook National University, Korea
Correspondent: Click to Email
Surface states of compound semiconductors are closely related to the undesirable characteristics of FETs such as transconductance dispersion, low breakdown voltage behavior, and low frequency noise. Recently, it was reported that the PL intensity was sharply increased by dipping GaAs wafer under intense light (photowashing treatment), which was explained by the reduction of surface states and the unpinning of surface Fermi-level. No works, however, were conducted on the effects of photowashing treatment on electrical properties of FET, especially AlGaN/GaN HFETs. In this work, we applied photowashing treatment on the ungated surface region between gate and source/drain electrodes of AlGaN/GaN HFETs and observed its effects on electrical characteristics using I-V and XPS. The AlGaN/GaN HFETs with a gate length of 1.0-micron were fabricated. The devices were photowashed by dipping them into deionized water under yellow room light. Photowashing time was varied from 1 to 30 minutes. The surface exposed under the same condition of photowashing treatment was characterized using XPS. In XPS measurement, it was found that the oxide was primarily composed of Al and Ga oxides. In I-V measurements, the drain current at gate biases corresponding to open channel and gate-to-drain reverse leakage current were simultaneously decreased. The decrease of drain current was explained by the increase of depletion width under the ungated surface region between gate and source/drain electrodes. This was evidenced by the decrease of binding energies of Ga 3d and N 1s photoemission spectra, namely, the movement of surface Fermi-level towards the valence band. On the other hand, the decrease of gate-to-drain leakage current was explained by the increase of negatively-charged surface states. From the changes of (Ga+Al) to N ratio at the surface of AlGaN by the treatment, the most probable point defect responsible for the movement of surface Fermi-level was discussed.