Tin oxide films: conductivity breakthrough could boost semiconductors

A thin, transparent, tin oxide film with record-breaking conductivity has been created for use in semiconductor applications such as next-generation LED lights, solar panels, and touch sensitive displays.
Shoichiro Nakao, a researcher at the University of Tokyo who worked on the material said: “We demonstrated the highest mobility in a thin film of tin oxide every achieved. Improved mobility not only enhances the conductivity but also the transparency of the material.”
Tin oxide films allow visible light and near infra-red light to pass through. Improved transparency would have a number of benefits, including, for example, improving the power conversion efficiency of photovoltaic solar panels.
“Generally, transparency and conductivity cannot coexist in a material. Typical transparent materials such as glass or plastic are insulating, whereas conducting materials like metals are opaque. Few materials exhibit transparent conductivity – it’s very interesting!” said Nakao.
The Tokyo team who developed the film explained their production methods were key to creating the unusual material. Nakao said: “We used a highly focused laser to evaporate pellets of pure tin dioxide and deposit or grow material exactly how we wanted it.”
The team replaced (doped) less than 1% of the tin in the evaporated tin dioxide with tantalum. The resulting tin-tantalum oxide (TTO) film was thinly deposited on a titanium dioxide surface using a laser. Including this small amount of tantalum improved the mobility of the film by 30%.
Tin-based oxide films are among the most used and studied metal oxide thin film materials for semiconductor applications due to their excellent optical and electronic properties. However, creating a thin tin oxide film with ultra-high mobility had previously eluded scientists due to difficulties growing a film with the right micro-structure.

Using their new production technique, the Tokyo team have successfully advanced mobility performance. The resulting material could further boost the use of tin in the many emerging light-sensitive, semiconductor applications.