Photoluminescence investigation of thin film a-Si:H-based structures passivated in cyanide solution

Abstract

We demonstrate the modification of photoluminescence (PL) spectra of Si-based thin film structures caused by the passivation process. The investigated samples consist of thin a-Si:H/ SiC:H layers deposited on clean crystalline Si(100) substrate. The structures were passivated by means of three types of chemical procedures based on aqueous and/or methanol solution of KCN. PL signals consist of a few partially overlapped Gaussian peaks. The shape of the PL spectrum is modified depending on the applied passivation method. This can be interpreted as a result of the diverse influence of the passivation on individual energy peaks. In our opinion, this confirms the assumption that the excited states that are contributing to the intensity of these peaks are localized in different zones of the sample, namely at different depths. We demonstrate the effect of substrate on the layers' structural parameters. Surface roughness was determined using the atomic force microscopy (AFM) method. X-ray diffraction at grazing incidence (XRDG) measurements confirm the non-homogeneity of deposited films that result in zones. The process of passivation modifies the densities of states that generate PL peaks differently in accordance with their localization. The diffusion of cyanide anions CN− in the amorphous matrix of the a-Si:H layer is the mechanism that controls this effect.