In recent years we have witnessed an explosion of interest in two dimensional (2D) materials, due to their unique physical properties. Excitement surrounds the promise of replacing conventional bulk photodetectors with devices based on 2D materials, allowing better integration, flexibility and potentially improving performance. However, the low inherent light absorption of 2D materials is an outstanding issue to be solved. In this chapter we review two independent approaches to tackling this problem, which have the potential to be combined to find a robust solution. The first approach involves patterning the substrate with a rod-type photonic crystal (PhC) cavity structure, which is shown to increase the light absorption into a 2D material flake coupled spatially to the cavity mode. Secondly, we review 2D–compatible solid immersion lenses (SILs) and their ability to increase both the optical magnification of the structures they encapsulate, and the longevity of the material. SILs have been shown to reduce the requirements for complex optics in the implementation of 2D materials in optoelectronic devices, and also in preserving the photodetector’s optical performance over long periods of time. Finally, we show how by combining rod-type PhC cavities with SILs, we can improve the performance of 2D material-based photodetectors.
Part of the book: Two-dimensional Materials for Photodetector
InAs-based nanowires hold a promise to offer transformational technologies for infrared photonic applications. Site-controlled InAs nanowire growth on low-cost Si substrates offers the practical integration advantages that silicon photonics benefits from. This includes the realisation of cheap photonic circuitries, light emitters and detectors that are otherwise expensive to realise with III/V material-based substrates. This chapter details the growth development of advanced faceted multi-quantum well structures within InAs nanowires using molecular beam epitaxy. We review the crystal structure for the faceted quantum wells along with an analysis of their optical emission characteristics which shows quantum confinement and localisation of the carriers on the quantum well nanostructure. This enables tuning of the emission wavelength and enhanced emission intensity up to the technologically important room-temperature operation point.
Part of the book: Nanowires