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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.

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