06-04-2021 | | By Robin Mitchell
Recently, researchers from NIMS and the Tokyo Institute of Technology have discovered a new compound that demonstrates semi-conductive properties with a direct bandgap that is non-toxic. Why are many semiconductor materials toxic, what has the joint research teams discovered, and how could it benefit the electronics industry?
Toxic compounds in products have always been a problem in human society. From lead pipes used by the Romans to asbestos insulation in houses, humans have tended to use toxic compounds in everyday objects. Of course, we cannot be blamed for using so many of these materials to start with as these materials generally exhibit great properties. For example, lead pipes are very easy to manipulate and use while asbestos has fantastic fireproofing capabilities.
However, when alternative materials are discovered that can perform the same function with non-toxic properties, it is our moral duty to replace those toxic materials with new non-toxic materials. This moral principle also applies to electronics, and the removal of toxic compounds not only benefits the users of electronics but also the environment once those components are disposed of and buried in a landfill.
Unlike resistors, capacitors, and inductors, semiconductors are not so easy to make non-toxic. This is due to the need for elemental compounds such as Boron, Cadmium, Lead, and Arsenic to change the properties of semiconductor materials. IC packing and leads are generally made from non-harmful compounds which help to reduce their overall toxicity, but the underlying semiconductor chip will typically contain environmentally harmful compounds.
Recently, a joint research effort by NIMS and the Tokyo Institute of Technology have discovered a new semiconductor material that has non-toxic properties. The new material is made from the compound Ca3SiO (Calcium Silicon Oxygen), which exhibits an inverse perovskite structure and has a narrow direct bandgap of around 0.9eV.
The direct narrow bandgap theoretically allows for the new material to be used in near-infrared optical applications, and non-toxic infrared semiconductors currently on the market cannot emit infrared photons. Furthermore, the research group is looking to develop high-intensity LEDs using the material as well as sensitive detectors by forming single crystals of the new compound.
The Discovery of the material was done using an uncommon approach; the team looked for crystalline structures using non-toxic elements whereby the silicon atoms behave as tetravalent anions instead of tetravalent cations. The exact reason why the research team looked for silicon cations instead of anions in a semiconductor structure was not explained, but it may be related to the position of Calcium and Oxygen on the periodic table (which would provide bandgap properties being on either end).
The small bandgap of the newly discovered semiconductor may not be suitable for generic semiconductor devices such as processors and memory modules, but its optical properties could be beneficial for the creation of near-infrared semiconductors. According to the researchers, the new compounds could be used in optic fibre and night vision applications due to their near-infrared properties.
Furthermore, the researchers also stated that the new semiconductor could be used in photovoltaics. One of the biggest challenges faced by solar panels is that they mostly absorb visible light and only around 50% of the infrared spectrum. As such, developing solar panels that can directly convert infrared to electricity would not only increase their efficiency but would also reduce the heating effect of the sun. This in turn will further help to improve efficiency as solar panels work best when cool.