Wide spectrum semiconductor light source from GaAs-bismide alloys.

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This project will explore the use of gallium arsenide-bismide alloys in infrared wavelength light emitting diodes. GaAs alloyed with bismuth, the heaviest group V element, is a narrow bandgap semiconductor alloy with interesting physical properties and a number of promising applications. In this project we explore the application of this material in one of these applications, namely as a light source for optical coherence tomography (OCT), a non-invasive medical imaging modality. The bismide alloys are attractive for this application for several reasons. Due to the unique electronic structure associated with Bi-alloying, the light emission spectrum from the material is much broader than for other III-V semiconductor alloys (~100nm). The width of the emission spectrum controls the resolution in OCT and is therefore an important figure of merit for an OCT light source. The reason for this anomalous behaviour is that Bi behaves in some respects as an impurity rather than as an alloying element. In addition when deposited on GaAs substrates the bismide alloys can cover the entire 850-1600 nm wavelength range of interest for OCT. Being compatible with the well established GaAs/AlGaAs laser technology they are amenable to high power operation and a mature manufacturing technology is available. The light source application is only one of a number of promising applications for the bismide alloys. The work in this proposal will advance the state of knowledge of growth