Structural characterization of silicon thin film superlattice grown at low temperature

Abstract

The growth of nc-Si:H from the SiH4 plasma inherently proceeds through a defective and amorphous incubation layer, originating due to the lattice mismatch between the substrate and Si material. In the current investigation, a-Si:H/nc-Si:H thin film super-lattice structures have been fabricated at very low temperature (∼180 °C), using single step conventional plasma processing. In this intriguing technique the a-Si:H barrier sub-layer itself operates as an effective incubation layer which facilitates growing the nc-Si:H active sub-layer possessing adequate crystallinity inside a very low thickness (tnc) of even ≥3 nm, and the sudden discontinuity in growth of the active layer confines the size of Si-ncs within the dimension of this active sub-layer thickness. The superlattice structure of the ultimate network has been evidenced from small angle XRD (SAX) measurements, whereas the nature of crystallinity has been studied by ellipsometry, Raman spectroscopy and electron microscopy. This simple yet compelling technique seems to have enormous technological implications taking the advantage of the quantum confinement effect in low dimensional silicon nano-crystallites within very thin superlattice structures.