High quality p-type binary composition films are very important for next generation low power complementary metal-oxide semiconductor thin film electronics such as microprocessors, batteries and digital camera sensors. Storm et al. proposed a new method to make thin films with properties close to bulk material in order to enable the best novel photonic and electronic thin film device properties.

Using copper iodide, a unique transparent p-type semiconductor, the researchers achieved a mobility record for thin films, which was about half of the best mobility reported for bulk material and much better than previous thin film results.

“It was a little surprising that we achieved such improved properties quickly,” said author Philipp Storm. “The paper shows that for CuI thin films, close-to-bulk quality is in reach.”

The researchers used a vacuum-based pulsed laser deposition method that allowed for optimization of growth conditions. Very little work has been done on optimized epitaxy, but it helped improve layer properties.

The researchers intend to combine well-researched n-type thin films transistors with this p-type material in order to develop a complementary technology, in particular inverters with one n-type and one p-type transistor that could result in energy-efficient and flexible thin film electronics.

“Our immediate research focus is on thin film transistors and integrated thin film electronic circuits. However, the light emission of CuI is very strong and so it is possibly an LED material too,” said Storm. Light emitting diodes are used widely in applications ranging from automotive headlamps to medical devices.

Source: “High mobility, highly transparent, smooth, p-type CuI thin films grown by pulsed laser deposition,” by P. Storm, M. S. Bar, G. Benndorf, S. Selle, C. Yang, H. von Wenckstern, M. Grundmann, and M. Lorenz, APL Materials (2020). The article can be accessed at https://doi.org/10.1063/5.0021781.