A research team composed of scientists in Japan and the UK has discovered a chemical compound that could be used to produce non-toxic infrared (IR) semiconductors. It would also be cheaper than the compounds currently used to produce such semiconductors.

The compound is composed of calcium, oxygen and silicon and its formula is Ca3SiO. It has been shown to be a ‘direct transition semiconductor’, which means it is capable of emitting IR radiation. Current non-toxic semiconductors are not capable of emitting IR radiation. 

Direct transition semiconductors are important because IR wavelengths have many uses, including in photovoltaic power generation, optical fibre communications and night vision devices. But current semiconductors of this type employ toxic chemical compounds, such as gallium arsenide and mercury cadmium telluride. 

“To discover infrared semiconductors free of toxic elements, this research group took an unconventional approach: they focused on crystalline structures in which silicon atoms behave as tetravalent anions rather than their normal tetravalent cation state,” stated the research group in its press release. “The group ultimately chose oxysilicides (eg Ca3SiO) and oxygermanides with an inverse perovskite crystalline structure, synthesised them, evaluated their physical properties and conducted theoretical calculations.”

(An atom which does not have a balanced number of protons and electrons, and so is electrically charged, is called a ion; anions have more electrons than protons and so are negatively charged while cations have more protons than electrons and thus are positively charged. Tetravalent means that the silicon atom can combine with four other atoms. In this context a perovskite is a synthetic compound that has a crystalline structure similar or identical to that of the naturally occurring mineral of the same name; in inverse perovskite structures, the position in the structure of anions and cations is reversed in comparison to standard perovskite structures.)

The research team now intends to develop high-intensity IR light-emitting diodes (which are basically semiconductors which emit radiation, usually visible wavelength light, when electrical currents are passed through them) by synthesising the compounds it has discovered. They will be synthesised as large single-crystals, by means of thin film growth processes resulting in their transformation into solid solutions. During these processes, their physical properties would be controlled by doping.

The research was undertaken by scientists at Japan’s National Institute for Materials Science, the Tokyo Institute of Technology and the University College London. Their results were published in the online edition of the American Chemical Society journal “Inorganic Chemistry”.