US Patent 7858166 Phase change recording medium

According to one embodiment, in a phase change optical disk which has a substrate and a multi-layered including an interference film, phase change recording film, interface film, and reflecting film, and in which information is reversibly recorded in or erased from the recording film by using light, an element (e.g., Ge or Te) forming the phase change recording film has segregation or a concentration distribution in the thickness direction of the recording film from a portion in contact with the phase change recording film.