Study On Silicon-nanocrystal-based Thin Films And Bulk Materials

Owing to size effect, Si nanocrystals (Si NCs) possess a variety of fantastic optical and electrical properties that are different from those of bulk silicon. Si-NC-based thin films hold great promise for applications in electronics, optoelectronics and photovoltaics. Bulk materials produced by using Si NCs also demonstrate potentials as energy materials.The structures and performance of thin films and bulk materials based on Si NCs have been investigated in this study.By the deposition of unintensionally doped Si NCs synthesized by non-thermal plasma with either a solution method or an all-gas-phase method, thin-film transistor s (TFTs) are successfully prepared. The carrier mobilities of the TFTs reach10-3cm2V-1S-1. The performace of the TFTs incidates that Si-NC-based thin films are slightly n-type-doped.Bulk materials are obtained by hot-pressing Si NCs heavily doped with B or P. The densities of the bulk materials are up to98%. They exhibit interesting electrical properties such as very low electrical resistivities (e. g.,0.803m Ω·cm) and very high carrier concentrations (e. g.,2.7x1020cm-3). During the hot pressing of Si NCs, Si NCs are sintered. The sintering is likely controlled by the viscous flow of Si NCs. It is believed that oxide at the NC surface contributes to the viscous flow of Si NCs and facilitates the realignment of Si NCs. Since P-doped Si NCs are more readily oxidized than B-doped Si NCs, P-doped Si NCs are better sintered than B-doped Si NCs. This leads to the fact that bulk materials obtained by using P-doped Si NCs are denser than those obtained by using B-doped Si NCs. It looks that the oxide at the NC surface is damaged during sintering so that the electrical transport of bulk materials is hardly affected by the oxide after sintering. Therefore, the electrical conductivity of bulk materials obtained by using P-doped Si NCs is excellent despite the initial easily formed oxide at the NC surface. The electrical conductivity of bulk materials obtained by using B-doped Si NCs is mainly limited by their porosity.