Thin Copper Iodide Film Will Improve Optoelectronic Devices

Semiconductors underlie many optoelectronic devices, including lasers and LEDs. Engineers

have long wanted to use copper iodide (examplehalide compound) in the creation of semiconductors. This compound is an excellent conductor of signals and is stable at temperatures above room temperature. The problem is that it is difficult to make a truly thin film of copper iodide without impurities. The usual method involves applying a film from a solution. “But the dissolution process is not suitable for creating high-quality copper iodide thin films,” explains Masao Nakamura from the RIKEN Center for New Materials Research.

Instead, Nakamura and his staffused an alternative method, molecular beam epitaxy, in which a film is gradually grown over a substrate at an elevated temperature and in a vacuum. Molecular beam epitaxy is already widely used in semiconductor manufacturing. However, this method is difficult to use for copper iodide. The fact is that this material is very volatile and easily evaporates during the process, and does not settle in the form of a film. To solve the problem, scientists tried growing the film at a lower temperature and then increasing it. It was this two-stage process that proved to be the most effective, the author of the study notes.

To improve the quality of the film, scientistsused as a substrate indium arsenide. Its structure is similar to that of copper iodide. This is important, because if the lattice spacing is not matched, many defects are formed in the material.

The authors of the development checked the purity of theirsample using photoluminescence spectroscopy. This method involves shooting photons (or particles of light) at the surface of a material. They are absorbed by the material, exciting its electrons to a higher energy state and causing them to emit new photons.

Monitoring the light emitted allowed the team to determine that they had created a defect-free monocrystalline film.

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