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Lay Summaries

Short descriptions of research carried out within the Cambridge Centre for Gallium Nitride intended for a general audience

A summary of my research for a general audience

Rachel Oliver 20/10/17


Light emitting diodes

Light emitting diodes (LEDs) based on gallium nitride (GaN) form the heart of modern energy efficient LED light bulbs.  However, the nitride crystals they exploit are full of imperfections, which might be expected to cause the LEDs to fail. My research caused the international community to rethink its understanding of why nitride LEDs work at all, which completely changes how device performance should be improved.  In particular, LEDs become less efficient as the amount of electrical current running through them increases, a problem known as "LED droop".  My work challenges conventional ideas about why this occurs, and suggests new ways forward.


Single photon sources

Whilst LED bulbs are increasingly common in the world around us, single photon sources (SPSs) are a future technology, which may revolutionise how we send information securely. This relies on the ability to emit exactly one fundamental particle of light (a photon). I invented the first SPS to exploit a material called indium gallium nitride (InGaN).  Many SPSs only operate at very low temperatures but my InGaN devices can operate at temperatures which could be attained inside a computer processor or a mobile phone. They can also emit photons on demand and at very high speeds in response to an external trigger.  Data must be encoded onto the properties of the photons, to create a stream of ones and zeroes.  For the photons emitted from my SPS, a specific property, termed polarisation, is unusually well controlled, which will make real communication systems more efficient.  My devices are the only SPSs in the world to combine all these useful attributes.


Nanoscale characterisation of nitrides

All of the above research is underpinned by my development of techniques to examine the structure and properties of nitride materials at very small scales - on the order of nanometres, where a nanometre is a millionth of a millimetre. I develop methods of using microscopes and X-rays to reveal information about nitrides and other materials which was previously inaccessible, and to link this information to the performance of a wide range of devices, not just the optoelectronic devices described above, but also electronic devices for use in data processing, power adapters and sensors.    


All of this work is intrinsically interdisciplinary, involving collaboration between materials scientists, engineers and physicists, sometimes within large consortia.