Abstract
The influence of hydrogen flow rate on the microstructure and optical properties of phosphorous doped hydrogenated amorphous silicon (a-Si:H(n)) films is studied through spectroscopic ellipsometry (SE). A series of a-Si:H(n) films were deposited using radio frequency plasma enhanced chemical vapour deposition (RFPECVD) technique by varying the hydrogen flow rate (HFR) in the range of 30–80 SCCM. The SE measurements showed a shift in peak position of pseudo dielectric function of these films from 3.6 eV (for pure a-Si:H) to 4.1 eV with a shoulder peak at 3.4 eV (nanocrystallites embedded a-Si:H) as the hydrogen flow rate was increased. A systematic increase in crystalline fraction along with a decrease in void fraction was observed as HFR was increased up to 70 SCCM during deposition. The results confirm that hydrogen dilution helps in improving the microstructure of films and favours the formation of strong Si–H bonds. Beyond 70 SCCM of HFR, a large flux of hydrogen resulted in an increase in void fraction and disorder in the films.
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