Comparative secondary ion mass spectroscopy analysis of solar cell structures grown by pulsed laser ablation and ion sputtering

We performed a complex secondary ion mass spectroscopy (SIMS) 3D analysis of solar cell structures based on II-VI semiconductors. The chemical composition analysis, as well as the depth distribution of the main elements and contamination were done for AuCu/CdTe/CdS/conducting glass structures. A structure where the II-VI compounds were grown by pulsed laser ablation (PLA) was compared with another structure grown by ion sputtering deposition (ISD). In both cases contamination due to O, C and H was found at high concentrations, particularly at the boundaries between crystallites. In addition to the SIMS depth profiling, the surface roughness (SR) was analysed by atomic force microscopy (AFM). Poor SIMS depth resolution was correlated to high surface roughness. The root-mean-square of the surface roughness (R-rms) was found to be higher for ISD than for PLA structures. In addition, the lateral distribution of the main components and contamination were observed in the microscope mode with a resolution of about 1 mum. A larger lateral contamination was correlated to a larger R-rms, of the analysed surface. Experimental 'diffusion' tails of Cu and Au from the ohmic contacts on the CdTe layer are also explained by a high R-rms for this layer.