Carbon-Free Solution-Based Doping for Silicon

Molecular doping is a method to dope semiconductors based on the use of liquid solutions as precursors of the dopant. The molecules are deposited on the material, forming a self-ordered monolayer that conforms to the surfaces, whether they are planar or structured. So far, molecular doping has been used with precursors of organic molecules, which also release the carbon in the semiconductor. The carbon atoms, acting as traps for charge carriers, deteriorate the doping efficiency. For rapid and extensive industrial exploitation, the need for a method that removes carbon has therefore been raised. In this paper, we use phosphoric acid as a precursor of the dopant. It does not contain carbon and has a smaller steric footprint than the molecules used in the literature, thus allowing a much higher predetermined surface density. We demonstrate doses of electrical carriers as high as 3 1015 #/cm2, with peaks of 1 1020 #/cm3, and high repeatability of the process, indicating an outstanding yield compared to traditional MD methods.