Nitride semiconductor laser device and a method for improving its performance

Abstract

The present invention relates to a nitride semiconductor laser device provided with a window layer on a light-emitting end face of the resonator which comprises an active layer of nitride semiconductor between the n-type nitride semiconductor layers and the p-type nitride semiconductor layers, in which at least the radiation-emitting end face of said resonator is covered by said window layer comprising monocrystalline nitride of general formula Al x Ga 1-x-y In y N, where 0≦x+y≦1, 0≦x≦1 and 0≦y<1, having a wider energy gap than that of the active layer and being formed at a low temperature so as not to damage said active layer. Formation of such a window layer improves significantly the performance of the nitride laser device according to the invention

1 . A method for improving the performance of a nitride semiconductor laser device having a resonator including an active layer comprising a nitride semiconductor between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer, comprising the steps of: 
 etching or cleaving a laser device structure and forming a pair of opposite resonator end faces, and    covering the radiation-emitting end face of the resonator by a window layer of monocrystalline nitride of general formula Al x Ga 1-x-y In y N, where 0≦x+y≦1, 0≦x≦1 and 0≦y<1, having a wider energy gap than that of the active layer, at low temperature so as not to damage the active layer.    
   
   
       2 . The method for improving the performance of a nitride semiconductor laser device according to  claim 1 , wherein said step of covering the end face of the resonator is in a supercritical ammonia-containing solution.  
   
   
       3 . The method for improving the performance of a nitride semiconductor laser device according to  claim 2 , wherein said step of covering the end face of the resonator is done after covering at least an upper surface of a resonator p-type contact layer by a mask having at least an equal chemical resistance as that of the material of the window layer in the supercritical ammonia-containing solution.  
   
   
       4 . The method for improving the performance of a nitride semiconductor laser device according to  claim 3 , wherein the mask is selected from the group consisting of SiO 2 , Si 3 N 4 , AlN and Ag.  
   
   
       5 . The method for improving the performance of a nitride semiconductor laser device according to  claim 1 , wherein said step of covering the end face is done by depositing the monocrystalline nitride layer in a supercritical ammonia-containing solution at a temperature of 800° C. or less.  
   
   
       6 . The method for improving the performance of a nitride semiconductor laser device according to  claim 5 , wherein said step of covering the end face includes depositing the monocrystalline nitride at 600° C. or less.  
   
   
       7 . The method for improving the performance of a nitride semiconductor laser device according to  claim 5 , wherein the monocrystalline nitride has a general formula of Al x Ga 1-x N (0≦x≦1).