Semiconductor laser device and method for fabricating the same

Abstract

In fabricating a semiconductor laser 10 with an oscillation wavelength of 770 to 810 nm, impurities are introduced into an MQW active layer 16 near a light emitting facet of the laser to form a disordered region constituting a window layer 20 . Pumped light is applied to the window layer 20 to generate photo luminescence whose wavelength λ dpl (nm) is measured. A blue shift amount λ bl (nm) is defined as the difference between the wavelength λ apl (nm) of photo luminescence generated by application of pumped light to the active layer 16 on the one hand, and the wavelength λ dpl (nm) of photo luminescence from the window layer 20 under pumped light irradiation on the other hand. The blue shift amount λ bl is referenced during the fabrication process in order to predict COD levels of semiconductor laser products.

What is claimed is:  
     
         1 . A semiconductor laser device with an oscillation wavelength of 770 to 810 nm, comprising: 
 a semiconductor substrate of a first conductivity type;    a first clad layer of the first conductivity type disposed on said semiconductor substrate;    an active layer of a quantum well structure disposed on said first clad layer;    a first second-clad layer of a second conductivity type disposed on said active layer;    a disordered region formed near a laser resonator facet by introducing impurities from a surface of said first second-clad layer into the layers including said active layer on said semiconductor substrate; and    an optical waveguide including a second second-clad layer of the second conductivity type disposed on the surface of said first second-clad layer in a manner opposite to said active layer in said disordered region across said first second-clad layer, said optical waveguide extending in a resonator lengthwise direction;    wherein if λ dpl is assumed to denote in nm the wavelength of photo luminescence generated by application of pumped light to said disordered region and λ apl to represent in nm the wavelength of photo luminescence generated by application of pumped light to said active layer, and if a blue shift amount λ bl in nm is defined as equal to λ apl−λ dpl, then the blue shift amount λ bl meets a condition of   λ bl≧20.   
     
     
         2 . A semiconductor laser device according to  claim 1 , wherein, if Pcod is assumed to denote in mW a COD level of the laser device, then the blue shift amount λ bl in nm further meets a condition of 
       (Pcod−85)/5.6≦λ bl≦(Pcod−135.0)/1.3. 
     
     
         3 . A semiconductor laser device according to  claim 1 , further comprising insulating films disposed on said first second-clad layer and on sides of said optical waveguide but not over a top portion of said optical waveguide.  
     
     
         4 . A semiconductor laser device according to  claim 2 , further comprising insulating films disposed on said first second-clad layer and on sides of said optical waveguide but not over a top portion of said optical waveguide.  
     
     
         5 . A semiconductor laser device according to  claim 1 , further comprising a current blocking layer of the first conductivity type disposed so as to bury said optical waveguide on said first second-clad layer.  
     
     
         6 . A semiconductor laser device according to  claim 2 , further comprising a current blocking layer of the first conductivity type disposed so as to bury said optical waveguide on said first second-clad layer.  
     
     
         7 . A semiconductor laser device fabricating method including the steps of: 
 firstly forming a first clad layer of a first conductivity type, an active layer of a quantum well structure, and a first second-clad layer of a second conductivity type successively on a semiconductor substrate of the first conductivity type;    secondly forming on a surface of the first second-clad layer a mask pattern for impurity implantation having an opening in a region where a resonator facet of a semiconductor laser device is expected to be formed;    thirdly disordering the active layer near the resonator facet by introducing impurities with the mask pattern for introducing impurity used as a mask;    fourthly applying pumped light to the disordered region to generate photo luminescence therefrom, and measuring a wavelength of the photo luminescence as a basis for predicting a level of COD degradation;    fifthly forming a second second-clad layer of the second conductivity type on the surface of said first second-clad layer after removing the mask pattern;    sixthly forming on a surface of the second second-clad layer a stripe-shaped mask pattern in a manner opposed to the disordered active layer across the first and the second second-clad layer, the stripe-shaped mask pattern extending in a resonator lengthwise direction; and    seventhly forming an optical waveguide including the second second-clad layer with the stripe-shaped mask pattern used as a mask.    
     
     
         8 . A semiconductor laser device fabricating method according to  claim 7 , wherein, if the semiconductor laser device has an oscillation wavelength of 770 to 810 nm; if λ dpl is assumed to denote in nm the wavelength of photo luminescence generated by application of pumped light to the disordered region and λ apl to represent in nm the wavelength of photo luminescence generated by application of pumped light to the active layer; and if a blue shift amount λ bl in nm is defined as equal to λ apl−λ dpl, then the blue shift amount λ bl meets a condition of 
       λbl≧20 
       when said fourth step is carried out.  
     
     
         9 . A semiconductor laser device fabricating method according to  claim 8 , wherein, if Pcod is assumed to denote in mW a COD level of the laser device, then the blue shift amount λ bl in nm further meets a condition of 
       (Pcod−85)/5.6≦λ bl≦(Pcod−135.0)/1.3.