The Synthesis, Simulations And Luminescence Properties Of Silicon Nanomaterials

Silicon is one of the most important materials in the area of microelectronic.However, the indirect band-gap structure restricts its further application inoptoelectronics. The transition from indirect to direct band-gap could open a way for theachievement of all-silicon optical communication, greatly facilitate the development ofsolar cell and solid-state luminescence devices, and also be available in the band-gapengineering in solid state physics.Silicon nanostructure is one of the possible candidates to realize the band-gaptransition. Systematical investigation on the band-gap structure of oxygen-passivatedsilicon nanonets (SiNNs) with different parameters were carried out. It was foundthat high porosity was favorable for the direct band-gap and the Si－O－Si bondcould effectively modify the band edge characteristic. Different funcionalgroups, such as－H,－O and－NH, were employed to terminate the danglingbonds of the SiNNs and silicon nanowires (SiNWs). It was found thatpassivation with－O functional groups could not only lead to the indirect todirect band-gap transition, but also enhance the transition efficiency andimprove the luminescene properites by increasing the electron states on the bandedge. State distribution effect were proposed to explain this phenomenon. Thestudy on the two dimensional silicon quantum films indicated that when the thicknessreached1.05nm and1.14nm for (100) and (110) quantum films, respectively, thedirect band-gap was also securable, which was attributed to the competition of quantumconfinement and surface electron states.In order to validate the models of SiNNs, metal-assisted chemical etching wasemployed to obtain the nanoscale and controllable porous structure on the nanowiressynthesized on the highly doped silicon wafer. A red luminescence band and anear-infrared one were detected in the photoluminescene (PL) measurement, whichwere attributed to interface recombination in the oxide layer and localized excitation inthe H-terminated porous structure, respectively. Selenization treatment was carried outon the porous SiNWs. An enhancement of30times of the luminescence intensity andwonderful stability were obtained. Time-resolved luminescence spetra proved that therecombination rate was three magnitudes faster after Seleniazation treatment. The lifetime of0.49ns and2.68ns were attributed to the recombination in the Si porousstructure passivated with Si－Se and Si－Se－O bonds, respectively. The fastrecombination rates indicated that surface modification induced by selenizationtreatment could lead to the direct radiative recombination in this Se-treated Siporous structure.The diameter of the SiNWs is crucial for its future application in optoelectronics.Ag-assisted chemical etching with polystyrene (PS) sphere as template was employed toprepare the SiNW arrays and the diameter could be controlled via high-temperatureoxidiation and etching. The core-shell nanowire arrays with silicon core diameter lessthan10nm was successfully synthesized due to the self-terminating effect. It isexpected that the structure parameter could be optimized in the future.