An epitaxial wafer, a method of manufacturing the epitaxial wafer, a diode, and a current rectifier are provided. The epitaxial wafer comprises a Si substrate layer; an insulating layer formed on the Si substrate layer; and a nitride semiconductor layer formed on a surface of the insulating layer facing away from the Si substrate layer; wherein the insulating layer has a thickness configured such that under a forward bias voltage, the insulating layer may allow electrons and holes to pass from one side to the other side of the insulating layer via quantum tunneling so as to allow a forward current flow.