Active doping of B in silicon nanostructures and development of a Si quantum dot solar cell

Abstract

Active doping of B was observed in nanometer silicon layers confined inSiO2 layers by secondary ion mass spectrometry (SIMS) depth profiling analysis and confirmed byHall effect measurements. The uniformly distributed boron atoms in the B-doped silicon layers of[SiO2 (8 nm)/B-dopedSi(10 nm)]5 films turned out to besegregated into the Si/SiO2 interfaces and the Si bulk, forming a distinct bimodal distribution by annealingat high temperature. B atoms in the Si layers were found to preferentiallysubstitute inactive three-fold Si atoms in the grain boundaries and thensubstitute the four-fold Si atoms to achieve electrically active doping. As aresult, active doping of B is initiated at high doping concentrations above1.1 × 1020 atoms cm − 3 and high activedoping of 3 × 1020 atoms cm − 3 could be achieved. The active doping in ultra-thin Si layers was implemented for siliconquantum dots (QDs) to realize a Si QD solar cell. A high energy-conversion efficiencyof 13.4% was realized from a p-type Si QD solar cell with B concentration of4 × 1020 atoms cm − 3.