Spray Pyrolysis of ZnO:In: Characterization of Growth Mechanism and Interface Analysis on p-Type GaAs and n-Type Si Semiconductor Materials

Sprayed transparent conductive oxides (TCOs) are an interesting alternative to sputtered TCOs for many applications due to the possible high throughput and a simple, atmospheric pressure process of spray deposition. In this work, the growth mechanism of sprayed ZnO:In was analyzed by transmission Kikuchi diffraction (TKD) analysis of the thin film's crystal orientation, which shows a preferred orientation of the growing grains and thus proves that the deposition occurs from the gas phase. It was observed that with increasing thickness of the layer, the average grain size increases and the measured resistivity significantly reduces to ≈5-6 × 10-3 Ω cm for layers of >500 nm thickness. Since many applications also require good electrical contact formation, the contact resistivity and the interface between sprayed IZO and n-type poly-Si and p-type GaAs, two materials that are commonly used in III-V/silicon tandem solar cells, were investigated by electrical measurements and high-resolution transmission electron microscopy (TEM) analyses. The interlayers observed in TEM were investigated by energy-dispersive X-ray spectroscopy (EDS) line scans. The results suggest that oxidic interlayers at the substrate/IZO interface are responsible for the observed higher contact resistivity compared to the contact resistivity of sputtered indium tin oxide (ITO) references. The results presented in this work lead to a better understanding of the deposition process occurring in spray pyrolysis and thus allow a more targeted optimization of process parameters depending on the future requirements of the application.