Photodiodes with pn-junction on both front and back sides

Abstract

The present invention is directed toward a dual junction photodiode semiconductor device. The photodiode has a semiconductor substrate of a first conductivity type, a first impurity region of a second conductivity type shallowly diffused on the front side of the semiconductor substrate, a second impurity region of the second conductivity type shallowly diffused on the back side of the semiconductor substrate, a first PN junction formed between the first impurity region and the semiconductor substrate, and a second PN junction formed between the second impurity region and the semiconductor substrate. Since light beams of a shorter wavelength are absorbed near the surface of a semiconductor, while light beams of a longer wavelength reach deeper sections, the two PN junctions at front and back sides of the photodiode allow the device to be used as an adjustable low pass or high pass wavelength filter detector.

1 . A dual junction photodiode semiconductor device comprising:
 a. a semiconductor substrate of a first conductivity type;   b. a first impurity region of a second conductivity type shallowly diffused on a first side of said semiconductor substrate, wherein the first impurity region has a first thickness and a first resistivity;   c. a second impurity region of the second conductivity type shallowly diffused on a second side of said semiconductor substrate, said second side being opposite to said first side, wherein the second impurity region has a second thickness and a second resistivity, wherein said first thickness is different than the second thickness, and wherein said second resistivity is different than the second resistivity;   d. a first PN junction formed between said semiconductor substrate and first impurity region; and   e. a second PN junction formed between said semiconductor substrate and said second impurity region.   
     
     
         2 . The dual junction photodiode semiconductor device of  claim 1 , wherein said first and second PN junctions are formed at a first depth and a second depth from a top surface of said semiconductor substrate, wherein the second depth is deeper than the first depth. 
     
     
         3 . The dual junction photodiode semiconductor device of  claim 1 , wherein said semiconductor substrate has a resistivity in a range of 4000 ohm-cm and a thickness of in a range of 400 microns. 
     
     
         4 . The dual junction photodiode semiconductor device of  claim 1 , further comprising:
 a. a first output electrode connected to said first impurity region;   b. a second output electrode connected to said second impurity region; and   c. a third output electrode connected to said semiconductor substrate, wherein said first and third output electrodes are output electrodes of the first PN junction, and said second and third output electrodes are output electrodes of the second PN junction.   
     
     
         5 . The dual junction photodiode semiconductor device of  claim 1 , wherein said first conductivity type is p+. 
     
     
         6 . The dual junction photodiode semiconductor device of  claim 5 , wherein said second conductivity type is n+. 
     
     
         7 . The dual junction photodiode semiconductor device of  claim 1 , wherein said first conductivity type is n+. 
     
     
         8 . The dual junction photodiode semiconductor device of  claim 7 , wherein said second conductivity type is p+. 
     
     
         9 . The dual junction photodiode semiconductor device of  claim 1 , further comprising an anti-reflective layer on said first side. 
     
     
         10 . The dual junction photodiode semiconductor device of  claim 9 , wherein the anti-reflective layer is about 1000 Angstroms thick. 
     
     
         11 . A multi junction photodiode semiconductor device comprising:
 a. a semiconductor substrate of a first conductivity type;   b. a low pass filter wherein said low pass filter comprises a first impurity region of a second conductivity type shallowly diffused on a first side of said semiconductor substrate, wherein an interface between said first impurity region and said first side of the semiconductor substrate forms a first PN junction;   c. a high pass filter wherein said high pass filter comprises a second impurity region of the second conductivity type shallowly diffused on a second side of said semiconductor substrate, said second side being opposite to said first side, wherein an interface between said second impurity region and said second side of the semiconductor substrate forms a first PN junction; and   d. wherein the low pass filter has a first thickness and a first resistivity, wherein the high pass filter has a second thickness and a second resistivity, wherein the first thickness is different than the second thickness and wherein the first resistivity is different than the second resistivity.   
     
     
         12 . The multi junction photodiode semiconductor device of  claim 11 , wherein said first and second PN junctions are formed at a first depth and a second depth from a top surface of said semiconductor substrate, wherein the second depth is deeper than the first depth. 
     
     
         13 . The multi junction photodiode semiconductor device of  claim 11 , wherein said semiconductor substrate has a resistivity in a range of 4000 ohm-cm and a thickness of in a range of 400 microns. 
     
     
         14 . The multi junction photodiode semiconductor device of  claim 11 , further comprising:
 a. a first output electrode connected to said first impurity region;   b. a second output electrode connected to said second impurity region; and   c. a third output electrode connected to said semiconductor substrate, wherein said first and third output electrodes are output electrodes of the first PN junction, and said second and third output electrodes are output electrodes of the second PN junction.   
     
     
         15 . The multi junction photodiode semiconductor device of  claim 11 , wherein said first conductivity type is p+. 
     
     
         16 . The multi junction photodiode semiconductor device of  claim 15 , wherein said second conductivity type is n+. 
     
     
         17 . The multi junction photodiode semiconductor device of  claim 11 , wherein said first conductivity type is n+. 
     
     
         18 . The multi junction photodiode semiconductor device of  claim 17 , wherein said second conductivity type is p+. 
     
     
         19 . The multi junction photodiode semiconductor device of  claim 11 , further comprising an anti-reflective layer on said first side. 
     
     
         20 . The multi junction photodiode semiconductor device of  claim 19 , wherein the anti-reflective layer is about 1000 Angstroms thick.