Silicon/germanium particle inks, doped particles, printing and processes for semiconductor applications

Abstract

Highly uniform silicon/germanium nanoparticles can be formed into stable dispersions with a desirable small secondary particle size. The silicon/germanium particles can be surface modified to form the dispersions. The silicon/germanium nanoparticles can be doped to change the particle properties. The dispersions can be printed as an ink for appropriate applications. The dispersions can be used to form selectively doped deposits of semiconductor materials such as for the formation of photovoltaic cells or for the formation of printed electronic circuits.

What is claimed is: 
     
         1 . A dispersion of silicon/germanium nanoparticles comprising a liquid and at least 0.1 weight percent silicon/germanium nanoparticles, wherein the silicon/germanium nanoparticles have an average primary particle diameter of no more than about 100 nm, a volume average secondary particle size of no more than about 250 nm and a surface modification moiety chemically bonded to the surface of the nanoparticles, wherein the dispersion has no settling without mixing after one week. 
     
     
         2 . The dispersion of  claim 1  wherein the surface modification moiety is bonded through a silane group. 
     
     
         3 . The dispersion of  claim 1  wherein the surface modification moiety is bonded to the silicon/germanium nanoparticles through a silicon atom, a carbon atom, a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a tellurium atom or a phosphorous atom. 
     
     
         4 . The dispersion of  claim 1  wherein the silicon/germanium particles have a distribution of primary particle sizes such that at least about 95 percent of the particles have a particle size greater than about 40 percent of the average diameter and less than about 250 percent of the average diameter. 
     
     
         5 . The dispersion of  claim 1  wherein the silicon/germanium nanoparticles comprise a dopant. 
     
     
         6 . The dispersion of  claim 5  wherein the dopant is selected from the group consisting of B, Al, Ga, P, As, and Sb. 
     
     
         7 . The dispersion of  claim 5  wherein the dopant concentration is at least about 1.0×10 −7  atomic percent relative to the silicon/germanium. 
     
     
         8 . The dispersion of  claim 1  comprising from about 0.1 weight percent to about 30 weight percent silicon/germanium nanoparticles. 
     
     
         9 . A method for surface modifying silicon/germanium nanoparticles, the method comprising blending the surface modifying composition into an initial stable dispersion of the silicon/germanium nanoparticles in a dispersing liquid wherein the silicon/germanium nanoparticles have a volume-average secondary particle size of no more than about 250 nm, wherein the silicon/germanium nanoparticles have an average primary particle size of no more than about 100 nm and wherein the surface modifying composition chemically bonds with the silicon/germanium particle surfaces to form surface modified nanoparticles with a surface modification moiety chemically bonded to the nanoparticle surfaces. 
     
     
         10 . The method of  claim 9  wherein the initial stable dispersion of silicon/germanium nanoparticles would exhibit no settling without mixing after one week. 
     
     
         11 . The method of  claim 9  wherein the surface modifying composition comprises an alkoxysilane. 
     
     
         12 . The method of  claim 11  wherein the alkoxysilane comprises a methoxy group or an ethoxy group. 
     
     
         13 . The method of  claim 9  wherein the surface modifying composition comprises a polydialkoxysiloxy silane. 
     
     
         14 . The method of  claim 9  wherein the dispersing liquid comprises alcohol or a blend of alcohol and water. 
     
     
         15 . The method of  claim 9  wherein the initial stable dispersion has at least 0.05 weight percent silicon/germanium nanoparticles. 
     
     
         16 . The method of  claim 9  wherein the silicon/germanium nanoparticles comprise a dopant. 
     
     
         17 . The method of  claim 16  wherein the dopant is selected from the group consisting of B, Al, Ga, P, As, and Sb. 
     
     
         18 . A printed substrate comprising a substrate surface having a selected pattern covering no more than about 90 percent of the surface area, the pattern comprising silicon/germanium nanoparticles in a coating layer having an average thickness from about 50 nm to about 5 microns, the nanoparticles having an average primary particle size of no more than about 100 nm, wherein the silicon/germanium nanoparticles have a distribution of secondary particle sizes such that at least about 95 percent of the secondary particles have a particle size greater than about 40 percent of the average particle size and less than about 250 percent of the average particle size. 
     
     
         19 . The printed substrate of  claim 18  wherein the silicon/germanium particles have a surface modification moiety chemically bonded to the surface of the nanoparticles. 
     
     
         20 . The printed substrate of  claim 19  wherein the surface modification moiety is bonded through a silane group. 
     
     
         21 . The printed substrate of  claim 18  wherein the silicon/germanium particles have a distribution of primary particle sizes such that at least about 95 percent of the particles have a particle size greater than about 40 percent of the average diameter and less than about 250 percent of the average diameter. 
     
     
         22 . The printed substrate of  claim 18  wherein silicon/germanium nanoparticles comprise a dopant. 
     
     
         23 . The printed substrate of  claim 22  wherein the dopant is selected from the group consisting of B, Al, G, P, As and Sb. 
     
     
         24 . The printed substrate of  claim 18  further comprising heating the substrate to sinter silicon/germanium nanoparticles.