The discovery of a semiconductor with performance better than silicon

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Without the semiconductor, there would be no digital (computers, smartphones, game consoles, etc.). Silicon is the most commercially used semiconductor material, due to its natural abundance and economical cost of implementation. However, semiconductor properties are not very good, and in the face of shortages due to the COVID-19 pandemic, many are looking for alternatives. Recently, a group of scientists from MIT showed that a material known as “cubic boron arsenide” fills the gaps in silicon and appears to be perhaps the best semiconductor known today. The next step is to find practical and economical ways to do this.

You should know that a semiconductor is a material that, in its pure state, does not conduct electricity, but becomes so following a certain treatment, doping. This semi-conduction is obtained by introducing impurities, through N doping (for negative, because electrons are added) or P (for positive, because electrons are removed): it increases the conductivity of semiconductors.

This treatment is used in the case of silicon, which is mainly the basis of photovoltaic cells that make up solar panels. The electrical conductivity of a semiconductor is intermediate between metals (good conductors) and insulators. In computers, several semiconductors are placed in a chain, alternating N doping and P doping, which allows the transmission of electrons from one to another. Electrons from the N-doped semiconductor fill the “holes” left by 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 poor. On the one hand, although it allows electrons to easily pass through its structure, it adapts to a smaller number of holes (P doping), making it difficult for electrons to pass through. These two properties are important in some types of chips. In addition, silicon is not very efficient at heating, so overheating issues and expensive cooling systems are common in computers.

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

Results confirm previous research

The current study builds on previous research, including the work of David Broido, co-author of the new paper. The latter predicts that cubic boron arsenide has a high thermal conductivity, almost 10 times greater than that of silicon. In addition, Chen’s team in 2018 also hypothesized that it is given a very high mobility for electrons and holes, ” what makes this material so unique Chen said in a statement. He added: ” This is important, because of course in semiconductors we have equal positive and negative charges. So when you’re building a device you want to have a material through which electrons and holes travel with little resistance “.

The electronic properties of cubic boron arsenide were originally predicted based on quantum mechanical density function calculations, performed by Chen’s group. Then, these predictions were confirmed by experiments carried out at MIT, using optical detection methods (through transient reflectivity microscopy) on samples made by Zhifeng Ren and his colleagues at the University of Houston.

Professor Shin explained: The critical step that made this discovery possible was advances in MIT’s ultrafast laser array system – originally developed by former MIT doctoral student Bai Song. Without this technique, it would not be possible to demonstrate the material’s high mobility for electrons and holes. “.

As mentioned earlier, one of the obstacles of silicon is its overheating and the need to invest in expensive cooling systems. For example, in the electronics of electric cars, silicon is replaced by silicon carbide, which has three times greater thermal conductivity. Simply put, it needs to heat up three times less to achieve the same efficiency as base silicon. However, through their experiments, the authors of the study confirmed 10 times higher thermal conductivity of cubic boron arsenide. Professor Shin points out: Imagine what boron arsenide can achieve, with 10 times greater thermal conductivity and greater mobility than silicon. This 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 small parts of the material that are the same to provide reliable data. Although they show the great potential of this material, ” we don’t know if or where it will be used Chen said.

Silicon is the workhorse of the entire electronics industry. In addition, the European Commission presented, Tuesday, February 8, 2022, a plan of 42 billion euros to promote the production of these electronic components. So more work is needed to determine if cubic boron arsenide can replace the ubiquitous silicon.

And although the thermal and electrical properties have been found to be very good, there are many other properties of this material that have not been tested, such as its long-term stability, explain the authors. Chen pointed out: Now that the desirable properties of boron arsenide are becoming clearer, suggesting that the material is ‘in many ways the best semiconductor’, perhaps more attention will be paid to this material. “.

However, the researchers concluded that, in the near future, the material will find uses where its unique properties can make a significant difference, if the industry provides the necessary funding for such development. -progress.

Source: Science

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