Patent ID: 11901378
Assignee: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Field: Semiconductors (Electrical engineering)
Classification: CPC H  G | IPC H

Claim 7:
8. A photodetector comprising:
two or more photodiodes each including a light absorption layer that contains germanium or a germanium compound, all cathodes or all anodes being interconnected;
a resistor connected in series with the cathodes or the anodes; and
a capacitor connected to a connection point between the resistor and the cathodes or the anodes, another connection point of the resistor being connected to a bias power supply, wherein
the resistor has a value between resistance values RAM and RM, both inclusive, determined by, [
  
   Math
   .
      
   3
  
  ]
 

 
  RAM
  =
  
   
    (
    
     El
     -
     
      Pbreak
      
       
        
         ∑
          
        
        
         n
         =
         1
        
        n
       
       ⁢
       
        M
        n
       
       ⁢
          
       PphotoAM_n
      
     
    
    )
   
   ⁢
   
    (
    
     1
     
      
       
        ∑
         
       
       
        n
        =
        1
       
       n
      
      ⁢
      
       M
       n
      
      ⁢
         
      PphotoAM_n
     
    
    )
   
  
 

 
  [
  
   Math
   .
      
   4
  
  ]
 

 
  RM
  =
  
   
    (
    
     El
     -
     V_M
    
    )
   
   ⁢
   
    (
    
     1
     
      
       
        ∑
         
       
       
        n
        =
        1
       
       n
      
      ⁢
      
       M
       n
      
      ⁢
         
      PphotoM_n
     
    
    )
   
  
 

where R is a resistance value of the resistor, E is an electric field applied to a depletion layer of each of the photodiodes, l is a depletion layer thickness of each of the photodiodes, Pbreak is breakdown power of each of the photodiodes, V_M is a value of voltage applied to each of the photodiodes when maximum operating optical input power is input to the photodiodes, M1 is sensitivity of a first of the photodiodes, M2 is sensitivity of a second of the photodiodes, as many sensitivities Mn as the number n of photodiodes being defined, PphotoAM_1 is maximum rated optical input power to the first photodiode and PphotoAM_2 is maximum rated optical input power to the second photodiode, as many maximum rated optical input powers PphotoAM_n as the number n of photodiodes being defined, and PphotoM_1 is maximum operating optical input power to the first photodiode and PphotoM_2 is maximum operating optical input power to the second photodiode, as many maximum operating optical input powers PphotoAM_n as the number n of photodiodes being defined, and
the electric field E×the depletion layer thickness l has a value between 7 V and 12 V.