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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 cost. However, its semiconductor properties are far from ideal, and in the face of shortages caused by the COVID-19 pandemic, many are looking for alternatives. Recently, a team of scientists from MIT showed that a material known as “cubic boron arsenide” fills the gaps in silicon and appears to be probably the best semiconductor known today. The next step is to find practical and economical ways to make it.
You should know that a semiconductor is a material which, in its pure state, does not conduct electricity, but becomes so following a specific treatment, doping. This semi-conduction is obtained by introducing impurities, by N doping (for negative, because electrons are added) or P (for positive, because electrons are removed): this increases the conductivity of the semiconductors.
This treatment is used in the case of silicon, which is in particular the basis of the photovoltaic cells which constitute the solar panels. The electrical conductivity of a semiconductor is intermediate between that of metals (good conductors) and that of insulators. In computers, several semiconductors are placed 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 in the “holes” left by the P-doping of the other semiconductor.
However, even though 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. Additionally, silicon is not very efficient at conducting heat, which is why overheating issues and expensive cooling systems are common in computers.
Recently, a team of researchers from MIT, the University of Houston, and other institutions demonstrated that cubic boron arsenide overcomes both of these limitations. It offers high mobility to 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 boron arsenide would have a high thermal conductivity, nearly 10 times greater than that of silicon. Additionally, Chen’s team in 2018 also hypothesized that it was endowed with very high mobility for electrons and holes, ” what makes this material truly unique says Chen in a statement. He adds : ” This is important, because of course in semiconductors we have equivalent positive and negative charges. So if you are building a device you want to have a material where electrons and holes travel with less 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 validated by experiments carried out 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 high mobility of the material 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 vehicles, 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 the 10 times higher thermal conductivity of cubic boron arsenide. Professor Shin points out: Imagine what boron arsenides can achieve, with 10 times greater thermal conductivity and far greater mobility than silicon. It can be a game changer “.
A new material with untapped potential
The challenge now is to find practical ways to manufacture 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 demonstrated the great potential of this material, ” we don’t know if or where it will actually be used said Chen.
Silicon is the workhorse of the entire electronics industry. Moreover, the European Commission presents, Tuesday, February 8, 2022, a plan of 42 billion euros to give a boost to the production of these electronic components. Further work will therefore be needed to determine if cubic boron arsenide can replace the ubiquitous silicon.
And although the thermal and electrical properties were found to be excellent, there are many other properties of this material that have not yet been tested, such as its long-term stability, explain the authors. 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, in the near future, the material could find uses where its unique properties would make a significant difference, if industry provides the necessary funding for such development.