Semiconductor laser diode and optical module

Abstract

The present invention provides a highly reliable ridge-waveguide semiconductor laser diode and an optical module. The p-side electrode of the ridge-waveguide laser diode has a first conductor layer region and a second conductor layer region formed on the first conductor layer region. At least one of facets of the second conductor layer region is recessed inward from a reflection facet. Thus, the ridge-waveguide semiconductor laser diode has a structure in which strain which is caused by the electrode stress to be applied on the diode facet is reduced and the saturable absorption does not occur. The ridge-waveguide semiconductor laser diode thus obtained is highly reliable, and the optical module using the same is remarkably high in reliability.

What is claimed is:  
     
         1 . A semiconductor laser diode comprising: 
 a semiconductor substrate;    a semiconductor layered body which is formed on the semiconductor substrate and has at least an active region;    a first electrode provided on the semiconductor substrate at a side opposite to a side on which the semiconductor layered body is formed; and    a second electrode provided at the side of the semiconductor layered body;    wherein: 
 the semiconductor layered body has a semiconductor layered portion on an upper region with respect to the active region thereof, the semiconductor layered portion being in the shape of a projection having its length in a light-propagating direction;  
 the second electrode on the semiconductor layered body side contacts an upper face of the projected semiconductor layered portion; and  
 the second electrode on the semiconductor layered body side includes a plurality of conductor layers, at least one of the conductor layers or a partial region which has a thickness larger than that of an edge of the conductor layer having a facet position of the conductor layer or an end position of the partial region which is thicker than the edge of the conductor layer at a position inside at least one of reflection facets constituting a cavity of the semiconductor laser.  
   
     
     
         2 . The semiconductor laser diode according to  claim 1 , wherein at least one of the plurality of conductor layers has both of its facets at positions recessed inward from both of the reflection facets constituting the cavity of the semiconductor laser.  
     
     
         3 . The semiconductor laser diode according to  claim 1 , wherein the semiconductor layered body comprises a first conduction type first cladding layer, the active region, a second conduction type second cladding layer and a contact layer which are deposited in this order, and the projected semiconductor layered portion is a semiconductor layered portion region including the second cladding layer and the contact layer.  
     
     
         4 . The semiconductor laser diode according to  claim 3 , comprising a semiconductor layer for carrier confinement in at least one of regions between the first conduction type first cladding layer and the active region and between the active region and the second conduction type second cladding layer.  
     
     
         5 . The semiconductor laser diode according to  claim 1 , wherein 
 the plurality of conductor layers constituting the second electrode on the semiconductor layered body side include a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region;    an insulator film is formed on side faces of the projected semiconductor layered portion, which are in parallel with the length of the projected semiconductor layered portion, and upper faces of the semiconductor layered body extending outwardly from the side faces;    the first conductor layer region and the second conductor layer region cover the upper face of the projected semiconductor layered portion and at least a part of the insulator film;    an edge of the first conductor layer region at the side of at least one of the reflection facets of the laser cavity is located at a position identical with that of the reflection facet; and    an edge of the second conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the edge position of the first conductor layer region.    
     
     
         6 . The semiconductor laser diode according to  claim 1 , wherein 
 edges of the first conductor layer region respectively at the sides of both of the reflection facets of the laser cavity are located at positions identical with those of the reflection facets; and    edges of the second conductor layer region respectively at the sides of both of the reflection facets are recessed inward from the edge positions of the first conductor layer region.    
     
     
         7 . The semiconductor laser diode according to  claim 1 , wherein 
 the plurality of conductor layers constituting the electrode on the semiconductor layered body side include a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region;    the second conductor layer region has a portion having a thickness thinner than that of a central portion thereof in the vicinity of a reflection facet of the laser cavity;    an edge of the thinner portion at the reflection facet side is located at a position identical with that of an edge of the first conductor layer region; and    an edge of the thicker portion at the reflection facet side is recessed inward from the edge position of the first conductor layer region.    
     
     
         8 . The semiconductor laser diode according to claim  7 , wherein 
 the thinner portion of the second conductor layer region is provided at each of the reflection facets of the laser cavity, and the edge of the thinner portion of the second conductor layer region at the reflection facet side is recessed inward from the edge position of the first conductor layer region.    
     
     
         9 . The semiconductor laser diode according to  claim 1 , wherein 
 the plurality of conductor layers constituting the first electrode on the semiconductor layered body side include a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region;    an insulator film is formed on side faces of the projected semiconductor layered portion, which are in parallel with the length of the projected semiconductor layered portion, and upper faces of the semiconductor layered body extending outwardly from the side faces;    the first conductor layer region and the second conductor layer region cover the upper face of the projected semiconductor layered portion and at least a part of the insulator film;    an edge of the first conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the reflection facet of the laser cavity; and    an edge of the second conductor layer region at the side of at least one of the reflection facets of the laser cavity is located at a position identical with that of the edge position of the first conductor layer region.    
     
     
         10 . The semiconductor laser diode according to  claim 9 , wherein edges of the first conductor layer region and the second conductor layer region are recessed inward from the reflection facets of the laser cavity at both sides of the reflection facets of the laser cavity.  
     
     
         11 . The semiconductor laser diode according to  claim 1 , wherein 
 the plurality of conductor layers constituting the electrode on the semiconductor layered body side include a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region;    an insulator film is formed on side faces of the projected semiconductor layered portion, which are in parallel with the length of the projected semiconductor layered portion, and upper faces of the semiconductor layered body extending outwardly from the side faces;    the first conductor layer region covers the upper face of the projected semiconductor layered portion and at least a part of the insulator film;    an edge of the first conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the reflection facet of the laser cavity; and    an edge of the second conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the edge position of the first conductor layer region.    
     
     
         12 . The semiconductor laser diode according to  claim 11 , wherein 
 edges of the first conductor layer region at the sides of both of the reflection facets of the laser cavity are recessed inward from the reflection facets of the laser cavity; and    edges of the second conductor layer region at the sides of both of the reflection facets of the laser cavity are recessed inward from the edge positions of the first conductor layer region.    
     
     
         13 . A semiconductor laser diode comprising: 
 a semiconductor substrate;    a semiconductor layered body which is formed on the semiconductor substrate and has at least an active region;    a first electrode provided on the semiconductor substrate at a side opposite to a side on which the semiconductor layered body is formed; and    a second electrode provided at the side of the semiconductor layered body;    wherein: 
 the semiconductor layered body has a semiconductor layered portion on an upper region with respect to the active region thereof, the semiconductor layered portion being in the shape of a projection having its length in a light-propagating direction;  
 the second electrode on the semiconductor layered body side contacts at least an upper face of the projected semiconductor layered portion;  
 the second electrode on the semiconductor layered body side includes a plurality of conductor layers, the plurality of conductor layers comprising a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region;  
 an insulator film is formed on a portion of at least one of the reflection facets of the laser cavity on the upper face of the projected semiconductor layered portion, side faces of the projected semiconductor layered portion, which are in parallel with the length of the projected semiconductor layered portion, and upper faces of the semiconductor layered body extending outwardly from the side faces;  
 the first conductor layer region covers the upper face of the projected semiconductor layered portion and at least a part of the insulator film;  
 an edge of the first conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the reflection facet of the laser cavity;  
 an edge of the second conductor layer region at the side of at least one of the reflection facets of the laser cavity is located at a position identical with the edge position of the first conductor layer region;  
 one facet of the insulator film formed on a part of the upper face of the projected semiconductor layered portion is located at a position identical with that of the reflection facet of the laser cavity; and  
 other facet of the insulator film formed on a part of the upper face of the projected semiconductor layered portion is located at a position identical with or recessed inward from the edge position of the first conductor layer region.  
   
     
     
         14 . The semiconductor laser diode according to  claim 13 , wherein 
 edges of the first conductor layer region and the second conductor layer region are recessed inward from the reflection facets of the laser cavity at both sides of the reflection facets of the laser cavity; and    the insulator film is formed on a portion of each of the reflection facets of the laser cavity on the upper face of the projected semiconductor layered body.    
     
     
         15 . The semiconductor laser diode according to  claim 13 , wherein 
 the plurality of conductor layers include a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region;    an insulator film is formed on a portion of at least one of the reflection facets of the laser cavity formed on the upper face of the projected semiconductor layered portion, side faces of the projected semiconductor layered portion, which are in parallel with the length of the projected semiconductor layered portion, and upper faces of the semiconductor layered body extending outwardly from the side faces;    the first conductor layer region covers the upper face of the projected semiconductor layered portion and at least a part of the insulator film;    an edge of the first conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the reflection facet of the laser cavity;    an edge of the second conductor layer region at the side of at least one of the reflection facets of the laser cavity is recessed inward from the edge position of the first conductor layer region;    one facet of the insulator film formed on the upper face of the projected semiconductor layered body is located at a position identical with that of the reflection facet of the laser cavity; and    other facet of the insulator film formed on the upper face of the projected semiconductor layered body is located at a position identical with or recessed inward from the edge position of the first conductor layer region.    
     
     
         16 . The semiconductor laser diode according to  claim 15 , wherein 
 edges of the first conductor layer region at the sides of both of the reflection facets of the laser cavity are recessed inward from the reflection facets of the laser cavity;    edges of the second conductor layer region at the sides of both of the reflection facets of the laser cavity are recessed inward from the edge positions of the first conductor layer region; and    the insulator film is formed on a portion of each of the reflection facets of the laser cavity on the upper face of the projected semiconductor layered portion.    
     
     
         17 . The semiconductor laser diode according to  claim 1 , wherein 
 the plurality of conductor layers constituting the electrode on the semiconductor layered body side include a first conductor layer region and a second conductor layer region which is formed on the first conductor layer region, the first conductor layer region having a plurality of layers of a titanium layer and a platinum layer or a plurality of layers of a titanium layer and a nickel layer and the second conductor layer region being a gold layer.    
     
     
         18 . The semiconductor laser diode according to  claim 1 , wherein 
 the second electrode on the semiconductor layered body side includes a tungsten silicide layer.    
     
     
         19 . The semiconductor laser diode according to  claim 1 , wherein 
 the plurality of conductor layers constituting the electrode on the semiconductor layered body side include a first conductor layer region which is close to the semiconductor layered body and a second conductor layer region which is formed on the first conductor layer region; and    the product of a distance from the edge of the first conductor layer region at the side of the reflection facet of the laser cavity to the edge of the second conductor layer region at the side of the reflection facet of the laser cavity and a sheet resistance of the first conductor layer region is 2 Ω·mm or less.    
     
     
         20 . An optical module comprising: 
 a substrate;    a semiconductor laser diode mounted on the substrate; and    a package having in its interior the substrate on which at least the semiconductor laser diode is mounted;    wherein: 
 the semiconductor laser diode comprises 
 a semiconductor substrate;  
 a semiconductor layered body which is formed on the semiconductor substrate and has at least an active region;  
 a first electrode provided on the semiconductor substrate at a side opposite to a side on which the semiconductor layered body is formed; and  
 a second electrode provided at the side of the semiconductor layered body;  
 the semiconductor layered body having a semiconductor layered portion on an upper region with respect to the active region thereof, the semiconductor layered portion being in the shape of a projection having its length in a light-propagating direction;  
 the second electrode on the semiconductor layered body side contacting an upper face of the projected semiconductor layered portion; and  
 the second electrode on the semiconductor layered body side including a plurality of conductor layers, at least one of the conductor layers or a partial region which has a thickness larger than that of an edge of the conductor layer having a facet position of the conductor layer or an end position of the partial region which is thicker than the edge of the conductor layer at a position inside at least one of reflection facets constituting a cavity of the semiconductor laser.