Gallium nitride vertical PIN diode and preparation method thereof

The invention provides a gallium nitride vertical PIN diode, and the diode comprises a substrate which is oppositely provided with a first surface and a second surface; a gallium nitride buffer layer epitaxially grown on the first surface of the substrate; a PIN junction which comprises an N + gallium nitride epitaxial layer, an intrinsic gallium nitride epitaxial layer and a P + gallium nitride epitaxial layer which are vertically grown on the gallium nitride buffer layer in sequence; an anode electrode arranged on the first surface, far away from the substrate, of the P + gallium nitride epitaxial layer; and a cathode electrode which comprises an ohmic contact electrode metal layer and a cathode metal layer, wherein the second surface of the substrate is provided with an etching groove, the etching groove at least extends to expose the N + gallium nitride epitaxial layer, the ohmic contact electrode metal layer is arranged in the etching groove and forms ohmic contact with the N + gallium nitride epitaxial