Effects of deposition pressure on the microstructural and optoelectrical properties of B-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films grown by hot-wire chemical vapor deposition

摘要

We report on the effects of deposition pressure P_d on the growth and properties of the B-doped nanocrystalline silicon (nc-Si:H) thin films grown by hot-wire chemical vapor deposition (HWCVD) at very high hydrogen dilution of 98.8%. We found that the crystallinity of nc-Si:H or μc-Si:H films is not only determined by hydrogen dilution but also the concentration ratio of atomic H to SiH_3 ([H]/[SiH_3]) on the growing surface which is varied with deposition pressure P_d. Furthermore, there is a threshold of [H]/[SiH_3] ratio which we name as overfull hydrogen (OH). When the [H]/[SiH_3] ratio is lower than the threshold OH ([H]/[SiH_3] < OH), the crystallinity of the nc-Si:H or μc-Si:H films increases with increasing [H]/[SiH_3] ratio. But when the [H]/[SiH_3] ratio is higher than the threshold OH ([H]/[SiH_3] > OH), the crystallinity decreases with increasing [H]/[SiH_3] ratio. Finally, the high conductivity of 4.22 S cm"' of the B-doped nc-Si:H thin film deposited at 15 Pa is obtained.