Influence of a substrate, structure and annealing procedures on crystalline and optical properties of Si/SiO2 multiple quantum wells

Several parameters affect the quality of nano-crystalline Si formed after annealing of Si/SiO2 multiple quantum wells (MQW). The main parameters influencing the quality are the substrate material, the structure of Si/SiO2, i.e. number of periods, thickness and composition of the layers and applied annealing procedures. This influence was investigated on MQWs fabricated by RPECVD of alternating Si-rich (amorphous Si and SiOX) and SiO2 layers on quartz and/or on sapphire substrates followed by annealing in rapid thermal annealing (RTA) mode and/or in a furnace. Number and thickness of layers were also varied for various samples. Properties of MQWs were investigated using Raman scattering and photoluminescence (PL) spectroscopy. Large stresses preventing full crystallization of nc–Si layers in MQW were reported previously. A value and a sign of the stress in the MQW layers were monitored by the characteristics of the nc–Si related Raman peak, i.e. spectral position and full-width-on-half-maximum of the peak. Our results show that the parameters of the stress could be largely tailored by changing substrate and/or structure of MQW. Obtained results show large possibilities for improvement of crystallinity of Si layers by choosing appropriate combination of MQW parameters (thicknesses and number of Si/SiO2 layers in MQW) and substrate material.