US 2002149026 A1 abstract a nitride semiconductor device having high electrode contact properties is disclosed the nitride semiconductor device includes a semiconductor layer made of a group iii nitride semiconductor and a metal electrode for supplying the semiconductor layer with a carrier the device has a first contact layer made of a group iii nitride semiconductor 1 u2212 y in y n laminated between the semiconductor layer and the metal electrode and a group ii element added thereto and a second contact layer made of a group iii nitride semiconductor al x u2032 ga 1 u2212 x u2032 n and laminated between the first contact and the metal electrode application_number US 10563302 A description in the following a device according to the present invention will be described in connection with embodiments with reference to the accompanying drawings 0030 fig1 illustrates a semiconductor light emitting device having a multi quantum well structure mqw according to the present invention the device comprises a multi layer structure having a plurality of nitride semiconductor crystal films represented by al x ga 1 u2212 x 1 u2212 y in y n 0 u2266 x u2266 1 0 u2266 y u2266 1 epitaxially grown in sequence on a substrate 1 made of sapphire on the substrate 1 made of sapphire a low temperature buffer layer 2 made of aln gan and the like and an n type gan underlying layer 3 doped with si or the like.