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Description
In search of a replacement for the expensive and scarce indium in indium-tin oxide (ITO), which is mostly used in transparent electrodes nowadays, zinc-tin oxide (ZTO) has proven to be a promising candidate.
In this study we present the effect of aging and oxygen content of the PtO$_\mathrm{x}$ contact on the efficiency of ZTO diodes. It is found that a high oxygen content in the sputter gas (>70%) is needed to produce functional devices with an on/off ratio of 10$^2$. It was also found that this further improves over time by a factor of 100 after 30 days. This is due to a strong reduction of current flow in backward direction, whereas the forward characteristics of the diodes stay the same. This indicates that the bulk of the ZTO remains unchanged and effects take place at the interface between PtO$_\mathrm{x}$ and ZTO, which reduce the leaking current.
It was found by depth resolved x-ray photoelectron spectroscopy measurements that at the interface a reduction of the PtO$_\mathrm{x}$ to Pt takes place. This effect was found to be more pronounced after aging of 30 days. This results suggest that the oxygen from the PtO$_\mathrm{x}$ contact diffuses into the ZTO and leads to a reduction of oxygen vacancies. This is assumed to yield a lower doping concentration in the vicinity of the interface and with this results in a spatially extended depletion region at the Schottky-contact compared to contacts with lower amounts of oxygen during deposition. This yields a reduction in tunneling current, which is responsible for the conducting behavior in backward direction for Pt contacts deposited without additional oxygen.
