Abstract
We report the effects of P incorporation on the nanometer-scale structural and electrical properties of amorphous and nanocrystalline mixed-phase Si:H films. In the intrinsic and weakly P-doped (3 × 1018 at/cm3) films, the nanocrystallites aggregate to cone-shaped structures. Conductive atomic force microscopy images showed high current flows through the nanocrystalline cones and a distinct two-phase structure in the micrometer range. Adding PH3 into the processing gas moved the amorphous/nanocrystalline transition to a higher hydrogen dilution ratio required for achieving a similar Raman crystallinity. In a heavily P-doped (2 × 1021 at/cm3) film, the nanocrystalline aggregation disappeared, where isolated grains of nanometer sizes were distributed throughout the amorphous matrix. The heavily doped mixed-phase film with 5-10% crystal volume fraction showed a dramatic increase in conductivity. We offer an explanation for the nanocrystalline cone formation based on atomic hydrogen enhanced surface diffusion model, and propose that the coverage of P-related radicals on the existing nanocrystalline surface during film growth and the P segregation in grain boundaries are responsible for preventing new nucleation on the surface of the existing nanocrystallites, resulting in nanocrystallites dispersed throughout the amorphous matrix. Crown
Original language | American English |
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Pages (from-to) | 2276-2281 |
Number of pages | 6 |
Journal | Journal of Non-Crystalline Solids |
Volume | 354 |
Issue number | 19-25 |
DOIs | |
State | Published - 2008 |
NREL Publication Number
- NREL/JA-520-41991
Keywords
- Amorphous silicon
- Atomic force microscopy
- Nanocrystalline materials
- Thin films