金属钝化多孔硅的制备、光致发光研究及电子结构计算

The properties of the photoluminescence (PL)/electroluminescence (EL) of porous silicon (PS) at room temperature make it possible to realize the full silicon-based photoelectronic integration without changing the traditional silicon planar technology. On the other hand, the peculiarity of its structure and surface morphology of PS, as well as its physical and chemical surface properties exhibited, might help PS find promising applications in the fields such as silicon-based sensors with high-sensitivity, ideal napped surface materials for novel solar cells, and templates for self-assembling of nanomaterials etc. But some essentional physical and technical problems about PS applications, such as the instability of the structure and PL, the strong dependence of its properties on preparation conditions, the mechanisms of the formation and PL, the electrical transportation properties, and the effective electrode developing techniques et al., are expected to be deeply investigated. Against the above problems, following researches on hydrothermally etched metal-passivated PS (MPPS) were carried out:1. Preparation, morphology control technique and formation mechanism. The time evolution properties of the silicon surface in the hydrothermal etching process were systematically investigated. The coexistence of two parallel etching mechanisms in the formation process, chemical etching and electrochemical etching, was proved and the different roles they played in formation process of the typical structure and surface morphology of MPPS were elucidated. Iron-, cobalt-, nickel-, manganese-, and titanium-passivated PS samples with stable PL and plentiful morphologies were fabricated. Through varying the conditions of hydrothermal etching, the control of the shape and size of the surface structural elements, as well as the structural homogeneity in large surface aera was realized. The effect of the electrical resistivity of the initial silicon wafers on the properties and surface morphologies of as-prepared MPPS were systematically studied. The existence of the critical resistivity value of initial silicon wafers in the hydrothermal process was found for the first time. It is disclosed that two different kinds of MPPS films, the physical sustained MPPS film (P-MPPS, the properties of PS film is related with the silicon substrate) and the mechanical sustained MPPS film (M-MPPS, the properties of PS film is independent of the silicon substrate), could be obtained by using silicon wafers whose initial resistivity is smaller or bigger than ~10-1Ωocm.2. Microstructure, PL and PL mechanism. Experimental study disclosed that MPPS is a typical silicon-based nanometer/submicrometer combined system, and at least on the scale of submicrometer, there exists tunable superstructures. Combined investigation on the properties of PL and submicrometer superstructures showed that the samples with homogeneous superstructures could also exhibit PL with good qualities, i.e., the stronger PL intensity and the narrower PL band. According to the quantum confinement theory of PL in PS, this result at least indicates that the qualities of the structures observed in two different scales, the nanometer scale and the submicrometer scale, of this nanomater/submicrometer combined system are strongly correlated, and which will directly affact the PL features. It is also disclosed that the intensity, the shape, and the peak position of both the Raman spectra and PL spetra have a reversible variation with the adopted excitation intensity, caused by the lattice distortion induced by laser irradiation. This phenomenon might explore novel optical applications for MPPS. At last, the calculation and fittings based on the experimental data of PL spectra and PL excitation spectra of MPPS were carried out, and these results are well agree with the pure theoretical results based on ab intial calculations adopted silicon quantum dot model. This agreement between theoretical calculation and experimental data fitting results provided strong support for the quantum confinement

利用本项目组成员发明的多孔硅原位金属钝化水热制备技术合成新型金属钝化多孔硅并研究其光致发光和结构特性；利用目前独有的大量有关铁钝化多孔硅的实验结果，从基于第一性原理的LDF－DVM方法出发，采用集团模型计算金属钝化多孔硅的电子结构以及硅－金属键钝化层对它的影响，建立金属钝化多孔硅发光的理论模型，为材料的应用作理论准备。