Chinese, South Korean scientists advance amorphous semiconductors

Scientists in China and South Korea say they have made a breakthrough in the development of amorphous semiconductors, with a new method that could lead the way to a new generation of semiconductor chip technology.

Complementary metal-oxide semiconductor (CMOS) technology, which is widely used to make memory chips and computer processors, helps to produce reliable integrated circuits that require low inputs of power.

Traditional CMOS technology integrates polycrystalline semiconductors, which are made up of many crystallised silicon grains that all have their own structure.

Amorphous semiconductors, which lack this order and have randomly distributed atoms, are more cost-effective, simple and uniformly manufactured, according to the team of researchers.

However the traditional amorphous hydrogenated silicon used in such applications “falls short in electrical properties, necessitating the exploration of new materials”, they wrote in a paper published as an accelerated preview in the peer-reviewed journal Nature on Wednesday.

The paper has undergone peer review but requires further proofing.

Creating amorphous semiconductors with high electron mobility – the speed at which an electron can move through a semiconductor – “holds the promise of enhancing scalable CMOS technology and facilitating the integration of multifunctional electronics,” the paper says.

However, challenges to developing suitable amorphous semiconductors have held back the development of new generation devices.

The team from Chengdu’s University of Electronic Science and Technology of China and the Pohang University of Science and Technology in South Korea say they have devised a “pioneering design strategy for amorphous p-type semiconductors,” that could make this possible.

The development of “thin-film transistors”, the technology that led to liquid crystal screen displays, has been propelled forward by the creation of high-mobility amorphous n-type semiconductors, the team said.

N-type semiconductors have an excess of electrons and fewer “holes”, which are when electrons in an atom move from the valence shell – where they normally reside – into the conduction band, where they can easily escape from an atom, creating a vacancy.

P-type semiconductors, on the other hand, have an excess of holes due to introduced impurities – which modifies their electrical properties.

Developing p-type semiconductors for CMOS has proved to be a major challenge, as the compounds used can only perform optimally in crystalline forms, the researchers said.

Crystalline forms have “low stability, complex synthesis processes, large-area non-uniformity, and a lack of industrial compatibility”, compared to amorphous forms, according to their paper.

However, the team found a strategy to use thermal evaporation to create a tellurium-based composite that could allow a commercially viable amorphous p-type semiconductor to become a reality. Tellurium is an emerging semiconductor material.

Their proposed strategy “exhibits superiority over reported emerging amorphous p-type semiconductors, exhibiting outstanding electrical performance, cost-effectiveness, high-stability, scalability” and processing potential, their paper says.

“This study represents a crucial stride towards establishing commercially viable” amorphous p-type semiconductors in a “low-cost and industry-compatible manner”, the team wrote. South China Morning Post