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Spontaneous miniaturization of self-assembled nc-Si-QDs with preferred 〈220〉 crystallographic orientation and a rapid synthesis of superior quality nc-Si-QD/a-SiC thin films with enhanced crystallinity, maintaining a combination of wide optical gap and simultaneous high electrical conductivity, has been attained from (SiH4 + CH4)-plasma, without any additional H2-dilution in inductively coupled plasma CVD. The optical gap widens due to the Si–C bonds in the amorphous network and the increased quantum confinement effect on the miniaturized Si-QDs. CH4 acts as the dual source of both C and atomic-H. High density of atomic-H available in the planar ICP promotes simultaneously the Si crystallization and its growth along the thermodynamically favored 〈220〉 crystallographic orientation, thereby contributing easier electrical transport, particularly at devices in superstrate configuration. After imminent doping, these could be efficiently utilized as window layers in third generation all-silicon solar cells.

In order to facilitate widening in optical band gaps utilizing quantum size-effects in silicon nano-crystals (Si-ncs) of a few nanometers in dimension, self-assembled Si-ncs embedded in an a-Si matrix were grown within a-Si:H/nc-Si:H superlattice (SL) thin films produced by alternating sub-layers of a-Si:H and nc-Si:H from (SiH4 + H2)-plasma in PE-CVD at 180 °C, without post-deposition annealing. The growth of Si-ncs extending all through the nc-Si:H sub-layer thickness is terminated by the alternate deposition of an a-Si:H barrier layer during each cycle and the average size of the Si-ncs with a narrow size distribution is tuned by controlling each nc-Si:H sub-layer thickness. Significantly high-density tiny Si-ncs are grown even within an ultra-thin (∼3 nm) nc-Si:H sub-layer and that has been made possible via an ingenious approach, by utilizing the underneath of an a-Si:H sub-layer as the virtual incubation layer at a very specifically chosen parametric condition, during each cycle of periodic deposition. On systematic thinning of the nc-S:H active layer within 8–3 nm, a remarkable increase in optical absorption at near-UV photon energies along with simultaneous optical band gap widening within 1.89–2.04 eV demonstrate that the quantum size-effect in Si-ncs plays a key role. Subsequent lowering in the defect states identifies the nc-Si:H/a-Si:H SL-films as a superior material for use in devices, including as i-layers in triple-junction all-silicon solar cells.