Functional materials and thermal conductivity research

Abstract

Harada’s research is focused on semiconductor crystals, in particular silicon carbide (SiC) and titanium oxides (TinO2n-1). Crystalline materials contain atoms that are arranged in a regular ordered pattern that is repeated throughout the material. Crystal semiconductors are useful because they sit somewhere between insulators and conductors in their ability to transfer electrical power and can be engineered to only conduct under certain conditions or in one direction only. These materials are ubiquitous today in integrated circuits, transistors, memory chips and processors and have made it possible to miniaturise these electronic components and continually improve power density and reliability. Silicon is still the most commonly-used semiconductor and forms the wafer substrate for integrated circuits in almost all electronic devices, from mobile phones to laptops and microwaves. The properties of the wafer can be manipulated through a process called doping, in which minute impurities are introduced to the silicon. Semiconductors are also used as thermoelectric devices that can convert waste heat energy into electricity. The applications for efficient devices of this nature are boundless since all energy use results in some wastage and often the waste energy exceeds the usable percentage. At present, these materials are not efficient enough to be widely applied except in cases where there is no alternative. Harada’s focus on SiC and TinO2n-1 is aimed at perfecting materials for both these applications for use in power devices and for the reclamation of heat energy as electrical power. In addition, he believes: ‘Future energy harvesting and production methods will also require us to manipulate heat energy.’ For all these applications, the material properties are dependent upon the presence or otherwise of atomic-scale defects. SiC is being studied as a next generation semiconductor material after silicon. Harada says: ‘Silicon carbide performs beyond the theoretical limits of silicon. It can cope with much higher temperatures, displays fewer voltages losses and conducts much higher voltages without affecting its properties.’ SiC is also a very versatile material and can be made to act either as a high-performance material for power devices or as an efficient thermoelectric material. These applications are the subject of two of Harada’s current research streams.