Phosphorus and Boron Doping Effects on Nanocrystalline Formation in Hydrogenated Amorphous and Nanocrystalline Mixed-Phase Silicon Thin Films

Abstract

Phosphorus and Boron doping effects on the microstructure of nanocrystallites in hydrogenated amorphous and nanocrystalline mixed-phase silicon films were investigated using Raman spectroscopy, secondary ion mass spectrometry, cross-sectional transmission electron microscopy, atomic force microscopy, and conductive atomic force microscopy. The characterizations revealed the following observations. First, the mixed-phase Si:H films can be heavily doped in ˜10²¹/cm³ by adding PH₃ and BF₃ in the precursor gases. Second, the intrinsic and doped films can be made in a similar crystalline volume fraction by adjusting hydrogen dilution ratio. The hydrogen dilution ratio is much higher for P-doped films than for the intrinsic film with the similar crystallinity. Third, the doping impacts the nanostructures in the films significantly. Nanograins aggregate to form cone-shaped clusters in the intrinsic and B-doped films but isolate and randomly distribute in amorphous tissues in the P-doped films. The cones in the intrinsic and B-doped films are also different. The cone-angle is smaller and the nanograin density is lower in the B-doped films than in the intrinsic films. These P- and B-doping effects on the nanocrystalline formation are interpreted in terms of diffusions of Si-related radicals during the film growth.