Doping properties of boron-doped microcrystalline silicon from B2H6 and BF3: material properties and solar cell performance

We have studied the doping properties of boron-doped hydrogenated microcrystalline silicon (μc-Si:H) deposited by glow-discharge plasmas of different SiH4/H2/B2H6 and SiH4/H2/BF3 gas mixtures. Regardless of dopant source gas, the solid-phase doping efficiency (hole/boron concentration ratio) increases monotonically as the boron concentration (CB) increases in the film, and it approaches unity at CB>1020 atoms/cm3, generating sufficient hole concentrations for solar cells. This doping behavior suggests that the impurity activation in μc-Si:H is independent of defect–compensation process in contrast to that in hydrogenated amorphous silicon. Although material properties reveal no dependence on the type of dopant source gas, μc-Si:H p–i–n solar cells with p-layers doped from BF3 provide higher conversion efficiencies than those from B2H6 at a lower CB range of <3 × 1019 atoms/cm3. Possible effects of the p-layer thickness on the doping properties are discussed.