The present invention provides an epitaxial structure of N-face group III nitride, its active device, and the method for fabricating the same. By using a fluorine-ion structure in device design, a 2DEG in the epitaxial structure of N-face group III nitride below the fluorine-ion structure will be depleted. Then the 2DEG is located at a junction between a i-GaN channel layer and a i-AlyGaN layer, and thus fabricating GaN enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs), hybrid Schottky barrier diodes (SBDs), or hybrid devices. After the fabrication step for polarity inversion, namely, generating stress in a passivation dielectric layer, the 2DEG will be raised from the junction between the i-GaN channel layer and the i-AlyGaN layer to the junction between the i-GaN channel layer and the i-AlxGaN layer.