CHARACTERIZATION OF HYDROGEN IN C-SI AND A-SI:H FROM AB-INITIO MOLECULAR DYNAMICS: STRUCTURE, OPTICS AND VIBRATIONS

摘要

Hydrogen (H), introduced into crystalline silicon (c-Si) or amorphous silicon (a-Si), is important for modifying Si properties required for solar cell (SC) photovoltaics. To establish a correlation of microscopic H bonding and distribution with the macroscopic properties of Si materials, and to assist in the theoretical interpretation of experimental spectra (from, e.g., non-destructive infrared or optical techniques) we carried out numeric experiments in the form of extensive finite temperature ab-initio molecular dynamics (AIMD) simulations, for both c-Si and a-Si:H. Starting with H implanted into c-Si and a-Si:H, we simulated the H dynamics, stability, and dissociation product evolution at various temperatures. For a-Si:H, realistic numerical samples are prepared by melting and subsequent annealing at different rates. The vibrational frequencies of hydrogen complexes such as bond-centered Hydrogen (BCH), H2* and H2** dimers are in good agreement with available experimental data. The complexes observed in AIMD are associated with characteristic features in the electronic and optical spectra of the host Si material.