Gallium nitride structure, piezoelectric element, method of manufacturing piezoelectric element, and resonator using piezoelectric element

A gallium nitride structure, comprising:

• a substrate;
• a gallium nitride layer provided so as to be opposed to the substrate and containing gallium nitride as a main component;
• and
• a first electrode that is provided between the gallium nitride layer and the substrate, the first electrode including at least one hafnium layer containing hafnium as a main component thereof the at least one hafnium layer in contact with the gallium nitride layer,
• wherein the at least one hafnium layer includes:
• a first hafnium layer that is in contact with the substrate;
• a second hafnium layer that is in contact with the gallium nitride layer;
• and
• a metal layer having a resistivity lower than hafnium between the first hafnium layer and the second hafnium layer.