DLTS analysis of interface and near-interface bulk defects induced by TCO-plasma deposition in carrier-selective contact solar cells

We investigate the electrical characteristics of defects at the SiO2/Si interface, within the adjacent Si crystal, and through the depth profile of the bulk defect using three-dimensional deep-level transient spectroscopy (3D-DLTS). These defects are introduced by the reactive plasma deposition technique employed for depositing transparent conductive oxides in the fabrication of carrier-selective contact-type solar cells. To control the surface potential near the Si surface, we apply a varying voltage to obtain DLTS signals as functions of both temperature and Fermi level at the SiO2/Si interface. Using machine learning for 3D-DLTS spectral analysis, we estimate the capture cross sections, energy levels, densities, and depth profiles of these process-induced defects. The experimental results indicate the existence of three types of electron traps within the bulk defects, ranging from the interface to a depth of ∼70 nm. The electrical properties of these bulk defects suggest the presence of oxygen-related defects within Si. On the other hand, regarding the properties of interface defects, the capture cross sections and the defect densities are estimated as a function of their energy levels. They suggest that the defects at the SiO2/Si interface are likely oxygen-related PL centers.