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M. Reiner, J. Schellander, G. Denifl, M. Stadtmueller, M. Schmid, T. Frischmuth, U. Schmid, R. Pietschnig, C. Ostermaier:
"Physical-chemical stability of fluorinated III-N surfaces: Towards the understanding of the (0001) Al_xGa_1-xN surface donor modification by fluorination";
Journal of Applied Physics, 121 (2017), S. 2257041 - 2257046.

Gallium nitride based high electron mobility transistors are widely known for their operational
instabilities regarding interface defects to the dielectric. In this paper, we discuss a III-N surface
treatment that results in an electrically more defined interface and hence a narrower distribution of
electrically present interface states compared to the original, untreated interface. This surface modification
is caused by a remote plasma fluorination of the III-N surface. We show that it is a very distinctive
surface processing which cannot be reproduced by other plasma techniques or ion
implantation. Applying physical and chemical analyses, the fluorination is found to have a remarkable
stability towards temperatures up to 700 C and is also stable in air for up to 180 h. However,
an aqueous clean allows the surface to return to its original state. Even though the exact physical
origin of the responsible surface donor cannot be inferred, we suggest that fluorine itself might not
directly represent the new surface donor but that it rather activates the III-N surface prior to the
dielectric deposition or even substitutes and hence reduces the concentration of surface hydroxides.