"The materials of the protective film 303 may include oxides such as silicon oxide (SiOx), silicon nitride (SixNiy), titanium oxide (TiOx) and zirconium oxide (ZrOx), nitrides, or multi-layer film thereof, as well as metals having a melting point higher than 1200??? C. These materials can stand at high temperatures ranging between 600??? C. and 1100??? C. at which nitride semiconductors can be grow" . . . .