Abstract
A semiconductor structure includes a first III-V compound layer. A second III-V compound layer is disposed on the first III-V compound layer and is different from the first III-V compound layer in composition. A source feature and a drain feature are disposed on the second III-V compound layer. A gate electrode is disposed over the second III-V compound layer between the source feature and the drain feature. A fluorine region is embedded in the second III-V compound layer under the gate electrode. A gate dielectric layer is disposed over the second III-V compound layer. The gate dielectric layer has a fluorine segment on the fluorine region and under at least a portion of the gate electrode.