Visible-swir hyper spectral photodetectors with reduced dark current

Abstract

A method includes forming an assembly of layers including an InP cap layer on an InGaAs absorption region layer, wherein the InGaAs layer is on an n-InP layer, and wherein an underlying substrate layer underlies the n-InP layer. The method includes removing a portion of the InP cap and n-InP layer by dry etching.

What is claimed is: 
     
         1 . A method comprising:
 forming an assembly of layers including an InP cap layer on an InGaAs absorption region layer, wherein the InGaAs layer is on an n-InP layer, and wherein an underlying substrate layer underlies the n-InP layer; and   removing a portion of the InP cap layer by dry etching.   
     
     
         2 . The method as recited in  claim 1 , further comprising:
 growing the InP cap layer epitaxially on the InGaAs absorption region layer; and   removing a portion of the InP cap layer by dry etching, leaving on the order of 10s of nm of the InP cap layer, wherein dry etching includes removing only on the order of nanometers of the InP cap layer.   
     
     
         3 . The method as recited in  claim 2 , further comprising forming a dielectric passivation layer on the InP cap layer after removal of the portion of the InP cap layer by dry etching. 
     
     
         4 . The method as recited in  claim 3 , further comprising forming a diffusion area in the InP cap layer and InGaAs absorption region layer to form a photodiode. 
     
     
         5 . The method as recited in  claim 2 , wherein dry etching is performed either a front illuminated detector or a backside illuminated detector. 
     
     
         6 . The method as recited in  claim 1 , wherein dry etching includes inductive coupled plasma (ICP) etching. 
     
     
         7 . The method as recited in  claim 6 , wherein the ICP is a chlorine free process. 
     
     
         8 . The method as recited in  claim 1 , wherein the n-InP layer is a contact layer for a back side illuminated detector, and further comprising:
 removing the substrate layer by chemical/mechanical polishing, selective wet etching of the substrate layer and sacrificial layers; and   dry etching a portion of the n-InP layer away.   
     
     
         9 . The method as recited in  claim 8 , wherein dry etching a portion of the n-InP layer away includes dry etching the n-InP layer down to a final thickness of less than or equal to hundreds of nanometers. 
     
     
         10 . The method as recited in  claim 8 , further comprising forming a multiple layer backside anti-reflective coating on the n-InP layer. 
     
     
         11 . The method as recited in  claim 1 , wherein dry etching includes dry etching the InP cap layer down to a thickness less than hundreds of nanometers that gives the assembly of layers sensitivity down into visible light wavelengths for hyper spectral imaging for front illumination. 
     
     
         12 . A photodiode system comprising:
 an InP cap layer on an InGaAs absorption region layer, wherein the InGaAs layer is on an n-InP layer, for front illumination wherein the InP cap layer is sensitive down into visible light wavelengths, wherein the InP cap layer is less than hundreds of nanometers thick.   
     
     
         13 . The system as recited in  claim 12 , wherein the InP cap layer and InGaAs absorption region layer include a diffusion area. 
     
     
         14 . The system as recited in  claim 13 , wherein the InP cap layer and InGaAs absorption layer have an inherent dark current reduced by dry etching for increasing pixel density due to reduced lateral diffusion. 
     
     
         15 . The system as recited in  claim 12 , and wherein an underlying substrate layer underlies the n-InP layer for front illumination. 
     
     
         16 . The system as recited in  claim 12 , wherein a sacrificial layer an underlying substrate layer underlie the n-InP layer for back illumination detectors are removed by chemical-mechanical lapping and polishing followed by selective wet etching, wherein the sacrificial layer is removed by wet etching, and wherein the n-InP layer is further thinned by dry etching. 
     
     
         17 . The system as recited in  claim 12 , further comprising a dielectric passivation layer on the InP cap layer. 
     
     
         18 . The system as recited in  claim 12 , wherein the n-InP layer has a thickness of less than or equal to hundreds of nanometers. 
     
     
         19 . The system as recited in  claim 12 , further comprising a multiple layer backside anti-reflective coating on the n-InP layer.