Banner image: Nitride LEDs being tested
Semiconducting materials underpin many of the modern technologies that we increasingly take for granted, such as tablets and mobile phones, and are also ubiquitous in data processing, systems control and power conversion in a vast range of less obvious contexts such as the automotive industry.
Much of the department's semiconductor research focused on gallium nitride and related materials, a fascinating family of semiconductors whose light-emitting properties have allowed the development of energy-saving LED light bulbs. We are also exploring nitride materials for a range of other applications, including power converters, radio frequency communications and sensors. Many of these devices exploit quantum structures: materials with at least one dimension so small that quantum effects control their properties. Some of our devices even directly use the quantum properties of single nanostructures. For example, we are developing single-photon sources for secure data communication and quantum computing applications based on single quantum dots, tiny semiconductor crystals only a few atoms in each dimension.
We also work on amorphous chalcogenides, exploited in storage-class memory. The memory is non-volatile (retained without applied bias) and is particularly suitable for low-powered portable devices. The data writing/erasing exploits the large change in resistance accompanying fast (0.1 to 100 ns) reversible amorphous-to-crystalline phase transitions. The mechanisms of these transitions are analysed, and the kinetics are measured for example using ultrafast calorimetry with achievable heating rates of 104 K/s.
Image below: Amorphous chalcogenides are also used in nano-ionic memory. On applying a voltage, dopant silver ions migrate and conducting filaments (the image shows a lateral geometry) grow, switching the memory to the ON state, a fast process that is easily reversed.