Photodetection and Spectrometry at the Nanoscale
Over the past fifteen years, one- and two-dimensional nanostructures have drawn intense attention across a range of scientific fields. For optoelectronic device applications these nanomaterials are particularly attractive due to their fundamental physical properties, such as dramatic environmental or photo-sensitivity, and effects arising from their sub-wavelength dimensions. Furthermore, their physical size alone presents an opportunity for their use as nanoscale components within miniaturised or flexible systems. In this thesis, optoelectronic device platforms based around two such nanomaterial systems – compositionally-engineered nanowires and layered black phosphorus – are developed and studied. An ultra-miniaturised microspectrometer device platform is demonstrated, based on individual compositionally-engineered nanowires. Representing the most compact microspectrometer design to date, by over two orders of magnitude, this strategy is independent of the complex optical components, cavities or CCDs that constrain further miniaturisation of current systems. It is demonstrated that incident spectra can be computationally reconstructed from the different spectral response functions and measured photocurrents along these nanowires. This platform is highly versatile; operation can straightforwardly be expanded across the infrared to ultraviolet range. Despite their simplicity, these devices are capable of accurate monochromatic and broadband light reconstruction, as well as spectral imaging from centimetre-scale image planes down to lensless, single-cell-scale in-situ mapping. This could open new opportunities for almost any miniaturised spectroscopic application, including lab-on-a-chip systems, smartphones, drones, implants, and wearable devices. Further to this, the first scalable strategy for depositing solution-processed black phosphorus films with viable device performance and stability is demonstrated. High concentration black phosphorus dispersions are produced by liquid-phase-exfoliation. Optimisation of a solvent-exchange method facilitates conversion of these dispersions into inks, which can be reliably inkjet printed to produce highly uniform black phosphorus films without significant flake degradation. Parylene-C encapsulation of these films ensures their long-term stability (>30 days) when incorporated into photodetectors and lasers, operating under intense irradiation without any observed drop in performance over time.