The researchers produced defective cuprous iodide films

According to foreign media reports, a fault-free film of cuprous iodide composed of a crystal has been created by physicists at RIKEN. Atomic planar samples are the driving force behind better semiconductors. Semiconductors are at the heart of many optoelectronic devices, including lasers and light-emitting diodes (leds). Engineers hope to use cuprous iodide in semiconductors because it is an excellent conductor that remains stable above room temperature.
The problem is that it is difficult to make a film of cuprous iodide that is truly free of impurities. The usual method is to precipitate the film from solution. “But this solution cannot produce high-quality films with cuprous iodide,” notes Masao Nakamura of the Centre for Emerging Matter Science in RIKEN.
Instead, Nakamaru and his colleagues used an alternative technique called molecular beam epitaxy, in which the film grows gradually on the substrate under high temperatures and a vacuum. Molecular beam epitaxy technology has been widely used in semiconductor production. But cuprous iodide is difficult to work with because the material is highly volatile — meaning it evaporates easily during processing without settling into a film. To overcome this, the team began by growing the film at a lower temperature and then raising it. “The two-step process that we developed is very effective,” Nakamura said.
The team had another way to improve the quality of the film. They chose indium arsenide as the substrate because its lattice spacing is very similar to that of cuprous iodide. “If the lattice spacing is not well matched, many defects will form in the material,” Nakamura noted.
Nakamura and his colleagues then tested the purity of the samples using a technique called photoluminescence spectroscopy, which involves emitting photons, or light particles, on the surface of the material. These photons are absorbed by the material, which excites its electrons to a higher energy state and causes them to emit new photons. Monitoring the emitted light allowed the team to determine that they had created a single crystal film without defects. “We want to use our approach to improve quality,” Nakamura says. But the results exceeded our expectations.”
Nakamaru and his team now plan to clamp together semiconductors made from different halides and study the resulting new properties. “We will explore new features and physics of the halogen interface,” he said.

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