Nitrides at the Nanoscale
Working in the Cambridge GaN centre, my research focuses on the characterization and exploitation of nanoscale structures in GaN-based materials. The broad aim of my work is to achieve improved performance in GaN-based optoelectronic devices and to develop and implement novel device concepts.
Nanoscale structure in nitride light emitting diodes and laser diodes
Nitride optoelectronic devices such as light emitting diodes (LEDs) and laser diodes (LDs) are in common use in a range of applications from bike lights to DVD players. However, particularly in the context of efficient home and workplace lighting, further improvements are required to maximise the potential of this technology in reducing the energy costs (and associated greenhouse gas emissions) of general illumination. By engineering the nanoscale structure of such devices, we can achieve not only improved efficiency, but also new functionality, such as polarised light emission (which is relevant for LED application in backlighting displays). My work in this area focusses on the characterisation and engineering of the structure of the light emitting active region of the devices and understanding how the nanoscale structure can profoundly influence macroscopic device performance.
Novel microscopy techniques for nitride semiconductors
To improve the performance of GaN-based devices we need to understand their structure and electronic properties on a micro- to nano-metre scale. New techniques are being developed to meet the demands of this unusual semiconductor. One of my current goals is to combine multiple microscopy techniques all focussed on the same defect or nanostructure in a nitride device. The microscopes applied range from techniques commonly used on metals (such as atom-probe tomography) to techniques which focus exclusively on semiconductors (such as scanning capacitance microscopy). My work requires the development of new approaches to the application of these techniques, to allow the same nanoscale regions of material to be assessed in multiple microscopes, so that the structure and composition of a specific nanostructure may be linked directly and unambiguously to its electrical and optical properties. Overall, the aim is to provide a more complete picture of nitride materials science than has previously been achieved, and to apply this new understanding to engineering improved materials for nitride optoelectronic devices.
GaN-based single photon sources
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. In contrast, we aim to build a single-photon source, based on InGaN quantum dots, that is reliable and easy to operate. 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. However, the high defect density and unusual electrical properties of GaN make realising the device a challenge.
For more information on Rachel's career and her role in the GaN centre read her researcher profile.