Backside nanoscale texturing to improve ir response of silicon solar cells and photodetectors

Abstract

The absorption coefficient of silicon for infrared light is very low and most solar cells absorb very little of the infrared light energy in sunlight. Very thick cells of crystalline silicon can be used to increase the absorption of infrared light energy but the cost of thick crystalline cells is prohibitive. The present invention relates to the use of less expensive microcrystalline silicon solar cells and the use of backside texturing with diffusive scattering to give a very large increase in the absorption of infrared light. Backside texturing with diffusive scattering and with a smooth front surface of the solar cell results in multiple internal reflections, light trapping, and a large enhancement of the absorption of infrared solar energy.

What is claimed is: 
     
         1 . A semiconductor imager capable of absorbing infrared light, comprising:
 a plurality of photodetectors each comprising:
 a semiconductor substrate having a substantially planar first surface available to receive incident radiation and a second surface opposite the first surface; and 
 a light diffusing region optically coupled to the second surface wherein the light diffusing region is configured to scatter light in a substantially Lambertian scattering pattern. 
   
     
     
         2 . The semiconductor imager of  claim 1 , further comprising a reflecting layer coupled to the light diffusing region. 
     
     
         3 . The semiconductor imager of  claim 1 , wherein the reflecting layer is comprised of a material selected from the group consisting of: oxide, silicon oxide, transparent conductive oxide, metals, and any combinations thereof. 
     
     
         4 . The semiconductor imager of  claim 1 , wherein the semiconductor substrate is comprised of silicon. 
     
     
         5 . The semiconductor imager of  claim 1 , wherein the semiconductor substrate has a thickness in the range of about 1 micrometers to about 10 micrometers. 
     
     
         6 . The semiconductor imager of  claim 1 , wherein the light diffusing region includes features being formed on or within the light diffusing region. 
     
     
         7 . The semiconductor imager of  claim 6 , wherein the features of the light diffusing region are selected from the group consisting of: cones, pyramids, pillars, protrusions, and combinations thereof. 
     
     
         8 . The semiconductor imager of  claim 1 , further comprising an anti-reflective layer disposed at the first surface of the semiconductor substrate and being transparent to infrared electromagnetic radiation. 
     
     
         9 . The semiconductor imager of  claim 8 , wherein the anti-reflective layer include features selected from the group consisting of cones, pyramids, pillars, protrusions, and combinations thereof. 
     
     
         10 . The semiconductor imager of  claim 9 , wherein the features of the anti-reflective layer are randomly distributed on or within the anti-reflective layer. 
     
     
         11 . The semiconductor imager of  claim 6 , wherein the features are formed by a process selected from the group consisting of: chemical etchants, plasma etching, porous silicon etchants, lasing, anisotropic etches, isotropic etches, masking techniques, nanoimprinting and combinations thereof. 
     
     
         12 . The semiconductor imager of  claim 1 , further comprising an oxide material coupled to the second surface of the substrate.