Nitride semiconductor device

Abstract

A nitride semiconductor device used chiefly as an LD and an LED element. In order to improve the output and to decrease Vf, the device is given either a three-layer structure in which a nitride semiconductor layer doped with n-type impurities serving as an n-type contact layer where an n-electrode is formed is sandwiched between undoped nitride semiconductor layers; or a superlattice structure of nitride. The n-type contact layer has a carrier concentration exceeding 3×10 10 cm 3 , and the resistivity can be lowered below 8×10 −3 Ωcm.

What is claimed: 
     
         1 . A nitride semiconductor light emitting device comprising:
 at least a substrate;   a buffer layer formed on said substrate;   an n-type contact layer doped with an n-type impurity for forming an n-electrode;   an active layer where electrons and holes are recombined; and   a p-type contact layer for forming a p-electrode, each layer being made of nitride semiconductor,   wherein said n-type contact layer has a first surface on which a first undoped nitride semiconductor layer is formed and a second surface on which a second undoped nitride semiconductor layer is formed to make a three-layer laminated structure, said three-layer laminated structure being situated between said buffer layer and said active layer.   
     
     
         2 . A nitride semiconductor light emitting device according to  claim 1 , wherein the second undoped nitride semiconductor layer has a thickness of more than 10 nm. 
     
     
         3 . A nitride semiconductor light emitting device according to  claim 1 , wherein said n-type contact layer is formed of GaN doped with Si as an n-type impurity, and said first undoped nitride semiconductor layer joined to the first surface of said n-type contact layer is formed of GaN or AlGaN while said second undoped nitride semiconductor layer joined to the second surface of said n-type contact layer is formed of one of GaN, AlGaN and InGaN. 
     
     
         4 . A nitride semiconductor light emitting device according to  claim 3 , wherein said n-type contact layer has a carrier density of more than 3×10 18 /cm 3 . 
     
     
         5 . A nitride semiconductor light emitting device according to  claim 3 , wherein said n-type contact layer has a resistivity of less than 8×10 −3  ohm cm. 
     
     
         6 . A nitride semiconductor light emitting device according to  claim 4 , wherein said n-type contact layer has a resistivity of less than 8×10 −3  ohm cm. 
     
     
         7 . A nitride semiconductor light emitting device according to  claim 1 , wherein said n-type contact layer has a super-lattice structure with a laminate of at least a nitride semiconductor layer (B layer) doped with an n-type impurity and an undoped nitride semiconductor layer(A layer). 
     
     
         8 . A nitride semiconductor light emitting device according to  claim 7 , wherein said n-type contact layer has a super-lattice structure of a laminate formed of a combination of nitride semiconductor layers selected from the group consisting of GaN/GaN, InGaN/GaN, AlGaN/GaN and InGaN/AlGaN and either one of which is doped with Si as an n-impurity. 
     
     
         9 . A nitride semiconductor light emitting device according to  claim 8 , wherein said n-type contact layer has a carrier density of more than 3×10 18 /cm 3 . 
     
     
         10 . A nitride semiconductor light emitting device according to  claim 8 , wherein said n-type contact layer has a resistivity of less than 8×10 −3  ohm cm. 
     
     
         11 . A nitride semiconductor light emitting device according to  claim 9 , wherein said n-type contact layer has a resistivity of less than 8×10 −3  ohm cm.