Discovery of a semiconductor with performance far superior to silicon

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Without a semiconductor, there is simply no digital (computers, smartphones, game consoles, etc.). Silicon is the most commercially used semiconductor material due to its natural abundance and economical implementation costs. However, its semiconductor properties are far from ideal, and in light of shortages due to the COVID-19 pandemic, many are looking for alternatives. Recently, a team of researchers from MIT showed that a material known as “cubic boron arsenide” fills the gaps in silicon and appears to be the best semiconductor known today. The next step is to find practical and economical ways to do it.

You must know that a semiconductor is a material which in its pure state does not conduct electricity, but becomes so after a certain treatment, doping. This semiconductor is achieved by introducing impurities, by N-doping (too negative, because electrons are added) or P (too positive, because electrons are removed): this increases the conductivity of the semiconductors.

This treatment is used in the case of silicon, which is especially the basis for the solar cells that make up the solar panels. The electrical conductivity of a semiconductor lies between that of metals (good conductors) and that of insulators. In computers, several semiconductors are arranged in a chain, alternating N-doping and P-doping, allowing the passage of electrons from one to the other. Electrons from the N-doped semiconductor fill the “holes” after the P-doping of the other semiconductor.

Illustration of (A) doping of two semiconductors and (B) principle of operation of chain semiconductors with passage of electrons between N and P. © Henry Laurie for Trust My Science

However, although silicon is widely used, its properties are not ideal. On the one hand, although it allows electrons to pass easily through its structure, it adapts much less to holes (P-doping), the passage of electrons is difficult. These two properties are nevertheless important in certain types of chips. In addition, silicon is not very efficient at conducting heat, which is why overheating problems and expensive cooling systems are common in computers.

Recently, a team of researchers from MIT, the University of Houston, and other institutions showed that cubic boron arsenide overcomes both of these limitations. It provides high mobility for electrons and holes and has excellent thermal conductivity. The work is published, through two simultaneous articles, in the journal Science.

Results that confirm previous research

The current study builds on previous research, including the work of David Broido, co-author of the new paper. The latter had theoretically predicted that cubic borarsenide would have a high thermal conductivity, nearly 10 times that of silicon. In addition, in 2018, Chen’s team also hypothesized that it was endowed with very high mobility of electrons and holes,” what makes this material truly unique Chen said in a statement. He adds: ” This is important because of course in semiconductors we have equivalent positive and negative charges. So if you’re building a device, you want a material where electrons and holes travel with less resistance “.

The electronic properties of cubic borarsenide were originally predicted based on quantum mechanical density functional calculations performed by Chen’s group. Then these predictions were validated by experiments conducted at MIT using optical detection methods (by transient reflectivity microscopy) on samples made by Zhifeng Ren and his colleagues at the University of Houston.

Professor Shin explains: The critical step that makes this discovery possible is advances in ultrafast laser array systems at MIT—originally developed by former MIT doctoral student Bai Song. Without this technique, it would not have been possible to demonstrate the material’s high mobility for electrons and holes. “.

As previously mentioned, one of the obstacles for silicon is its overheating and the need to invest in expensive cooling systems. For example, silicon in electric vehicle electronics is replaced by silicon carbide, which has three times the thermal conductivity. In short, it needs to be heated three times less to achieve the same efficiency as base silicon. However, through their experiments, the authors of the study confirmed the 10 times higher thermal conductivity of cubic borarsenide. Professor Shin points out: Imagine what boron arsenides can achieve with 10 times greater thermal conductivity and far greater mobility than silicon. It could be a game changer “.

A new material with untapped potential

The challenge now is to find practical ways to produce this material in usable quantities. Current manufacturing methods produce material that is not uniform, so the team had to find ways to test only small areas of the material that were uniform enough to provide reliable data. Although they showed the great potential of this material, ” we don’t know if or where it will actually be used Chen says.

Silicon is the workhorse of the entire electronics industry. Furthermore, on Tuesday, February 8, 2022, the European Commission presents a 42 billion euro plan to boost the production of these electronic components. Further work will therefore be needed to determine whether cubic boron arsenide can replace the ubiquitous silicon.

And while the thermal and electrical properties proved to be excellent, there are many other properties of this material that have yet to be tested, such as its long-term stability, the authors explain. Chen points out: Now that the desirable properties of boron arsenide have become clearer, suggesting that the material is ‘in many ways the best semiconductor’, perhaps more attention will be paid to this material “.

Still, the researchers conclude that the material may find applications in the near future where its unique properties would make a significant difference if the industry provides the necessary funding for such development.

Source: Science

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