Optical semiconductor device and pumping light source for optical fiber amplifier

Abstract

A semiconductor device of the invention is formed so that n-type InP current blocking layers enter the inside of p-type InP cladding layers, i.e., the n-type current blocking layers ride over the upper part of the p-type InP cladding layers, so that a distance between the n-type InP current block layers composing a current blocking region is narrower than a width of the p-type cladding layers contacting with the n-type InP current blocking layers. Thereby, the semiconductor device whose leak current in the current blocking region may be reduced which permits high-output and high-temperature operations may be readily fabricated.

What is claimed is: 
     
         1 . A method of producing an optical semiconductor device, comprising the steps of:
 preparing a semiconductor substrate, forming a first cladding layer on one flat surface of said semiconductor substrate,   forming an active layer on said first cladding layer,   forming a second cladding layer on said active layer;   forming said first cladding layer, said active layer and said second cladding layer as a mesa-shape structure,   forming first current blocking layers of a first conductive type on said first cladding layer, said active layer and a part of said second cladding layer at both side surfaces of said mesa-shape structure,   forming second current blocking layers of a second conductive type as covering said first current blocking layers;   wherein in the step of forming said first current blocking layers and the step of forming said second current blocking layers, said first current blocking layers and said second current blocking layers are formed by metal-organic vapor phase epitaxy, and   in the step of forming said second current blocking layers, said second current blocking layers are formed so that upper surfaces of said second current blocking layers are same or substantially same as an upper surface of said second cladding layer and said second current blocking layers have a structure wherein end portions of said upper surfaces of said second current blocking layers extend over said first current blocking layer, and ride over said second cladding layer so as to enter the inside of said second cladding layer by the mass-transport phenomenon.   
     
     
         2 . The method of producing an optical semiconductor device according to  claim 1 , wherein said second current blocking layers are formed as films deposited at a deposition temperature T satisfying that the following formula is negative regarding said deposition temperature T of said second current blocking layer
     W 1- W 2(μm)=−0.0092× T+ 6.18,
   where,   W 1  is a distance between said end portions of said second current blocking layers and   W 2  is a width between said first current blocking layers contacting said second cladding layer.   
     
     
         3 . The method of producing an optical semiconductor device according to  claim 2 , wherein in the step of forming said first current blocking layers and the step of forming said second current blocking layers, said first current blocking layers and said second current blocking layers are formed so that the (W 1 -W 2 ) satisfies −0.5 μm≦(W 1 -W 2 )<0 μm. 
     
     
         4 . The method of producing an optical semiconductor device according to  claim 1 , wherein in the step of forming said second current blocking layers, said second current blocking layers are formed so that concentration of said first conductive type impurity of said first current blocking layers is in a range from 0.8×10 18  cm −3  to 1.4×10 18  cm −3 .  
     
     
         5 . The method of producing an optical semiconductor device according to  claim 1 , wherein in the step of preparing said semiconductor substrate, a semiconductor substrate comprising InP is prepared. 12/8003-FDK-US (FRKWP147USA) 
     
     
         6 . The method of producing an optical semiconductor device according to  claim 5 , wherein in the step of forming said active layer, said active layer is formed so as to have a quantum well structure or a strain super-lattice quantum well structure. 
     
     
         7 . The method of producing an optical semiconductor device according to  claim 6 , wherein in the step of forming said active layer, said active layer is formed so that a width of said active layer is selected so as to meet a single-transverse mode operation across a light waveguide direction. 
     
     
         8 . The method of producing an optical semiconductor device according to  claim 1 , further comprising a step of forming films having different reflectivity on the both end surfaces in a resonator direction of said optical semiconductor device. 
     
     
         9 . The method of producing an optical semiconductor device according to  claim 6 , wherein in the step of forming said active layer, said active layer is formed so as to comprise GaInAsP. 
     
     
         10 . The method of producing an optical semiconductor device according to  claim 7 , wherein in the step of forming said active layer, said active layer is formed so as to contain an active layer in which thickness of a well layer is 6 nm or more. 
     
     
         11 . The method of producing an optical semiconductor device according to  claim 6 , wherein in the step of forming said active layer, said active layer is formed so as to comprise AlGaInAs. 12/8003-FDK-US (FRKWP147USA) 
     
     
         12 . The method of producing an optical semiconductor device according to  claim 1 , wherein in the step of forming said first current blocking layers and the step of forming said second current blocking layers, said first current blocking layers and said second current blocking layers are formed so as to establish pn junction or np junction.