Silicon Nanodot Layers for Photovoltaic Application: Size/Density Control and Electrical Properties

Abstract

Abstract Fabrication of Si nanodot single layers under ultrahigh vacuum (UHV) conditions is achieved by decomposition and self-organized growth from thermally deposited non-stoichiometric SiO x (x < 2) precursor layers provided with an ultrathin SiO2 capping layer due to phase separation upon appropriate in situ annealing. The kinetics of the thermal decomposition of the constituting Si suboxides (Si n+, n = 0…4) into Si nanodots and the surrounding SiO2 matrix is analyzed in situ by X-ray photoelectron spectroscopy (XPS) as a function of the annealing temperature. The maximum size and the density of the nanodots are varied by adjusting the stoichiometric coefficient x and the layer thickness. Thus, the electronic nanodot properties and the interlayer transport properties can be controlled. For initial compositions (x ranging from 0.9 to 1.4) and layer thicknesses (3 to 10 nm), phase separation was completed at 850 ℃. The phase separation revealed by XPS is directly correlated with electrical properties as derived from atomic force microscopy measurements detecting surface potentials (KFM) and local conductivity (CS-AFM) across individual nanodots.