Size-dependent phosphorus doping effect in nanocrystalline-Si-based multilayers

Abstract

Doping in Si nanocrystalline (Si NCs) is currently an interesting issue since it can modulate electronic structures of Si NCs and consequently affect the electric and optical properties. However, it has been reported that doping in Si NCs is quite difficult due to the self-purification effect and the locations of dopants such as phosphorus (P) and boron (B), as well as the influences of dopants on physical properties is still unclear. In the present work, the P-doped Si NCs/SiO2 multilayers with various dot sizes (2–20 nm) were fabricated. It is found that the electronic properties are enhanced significantly after doping. However, for P-doped samples, the conductivity is size-dependent and reduces with decreasing the dot size, which can be attributed to the reduction of activated carrier concentration in the film with small dot size. Moreover, we find P dopants can induce deep-level for sample with small size of 2 nm, and a sub-band near infrared light emission near 1250 nm is detected. The possible mechanism are discussed briefly.