Zincblende GaN is just one of the novel nitrides studied in the Cambridge Centre for Gallium Nitride. This is because the zincblende structure can be used to avoid internal electric fields which arise as a consequence of the low symmetry of wurtzite crystals and degrade the efficiency of wurtzite light emitters. However, the alternative metastable zincblende structure may offer solutions to some of the enduring problems of nitride technology, such as the relatively low efficiency of red, green and amber nitride LEDs. GaN in its stable wurtzite crystal structure has achieved amazing things in both electronics and optoelectronics. We are also interested in developing crystal growth routes which allow improved heat dissipation from nitride devices, and which enable new or enhanced device functionality. Typical nitride transistors have very high densities of defects, and one of our research foci is understanding the impact of these defects on device performance. Whilst the nitrides have superior materials properties, they are a much less mature materials system than Si. However, GaN can endure greater electric fields than silicon, and GaN-based devices can be made with lower resistances. In the control and conversion of electric power, silicon-based devices are no longer able to meet the demands of industry. Nitride transistors are increasingly used in high frequency, high voltage, high temperature and high efficiency applications. However, the high defect density and unusual electrical properties of GaN make realising the device a challenge. Such a device would find broad application in quantum cryptography and quantum computing, particularly as the emission wavelength of the InGaN dots is rather convenient in terms of available detectors. In contrast, we aim to build a single-photon source, based on InGaN quantum dots, that is reliable and easy to operate. Early single-photon sources emitting in the visible spectral region were based on heavy attenuation of a laser such sources are intrinsically unreliable, and may emit multiple photons. However, research on nitride optoelectronics extends far beyond the humble LED, and increasingly encompasses exotic devices such as single photon sources.
Hence, our research on LEDs focusses on the links between the structure of the nitride materials and the performance of the devices, and how the structure – particularly of the active, light emitting region – can be engineered to improve efficiency. Whilst the blue LEDs use in such light bulbs are a tremendously successful technology, nitride LEDs at other wavelengths – from the red to the ultra-violet – suffer from low efficiencies.
The semiconducting nitrides are a key optoelectronic material, which enabled the development of energy efficient light bulbs based on light emitting diodes (LEDs). The broad aim of my work is to achieve improved performance in GaN-based electronic and optoelectronic devices and to develop and implement novel device concepts.Ĭambridge is also the main supplier of nitride epitaxy in the EPSRC National Epitaxy Facility (NEF), and provides nitride materials to academics across the UK ( ). She was interviewed about her experiences by Chemistry World.Īs Director of the Cambridge Centre for Gallium Nitride, Prof Oliver’s research interests focus on the characterization and exploitation of nanoscale structures in GaN-based materials. Prof Rachel Oliver has benefitted from the University's policies on flexible working, in line with the Department's commitments to the Athena Swan Charter.
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