Hydrogenated amorphous silicon for nano-photonic devices from visible to mid-infrared

Silicon photonics has become the dominant technology for integrated photonic devices. It supports low power consumption, dense integration with CMOS electronics, low cost and is, therefore, promising for high-performance... [ view full abstract ]

Silicon photonics has become the dominant technology for integrated photonic devices. It supports low power consumption, dense integration with CMOS electronics, low cost and is, therefore, promising for high-performance communication and computing. Crystalline silicon (c-Si) has been the main platform; however, high-quality c-Si is impossible to grow on a foreign substrate, implying that it cannot be used for advanced multilayer photonic integration. Hydrogenated amorphous silicon (a-Si:H) is emerging as an alternative in this perspective. A distinct advantage of a-Si:H comes from the fact that it can be deposited easily at low temperature on almost any substrates, facilitating back-end integration of a-Si:H photonic components on top of pre-processed CMOS electronic chips without any damage to the underlying metal wires. Despite of the recent progress in fabricating high quality devices, however there have been few studies of a-Si:H for 3-dimensional integrated photonic chips.In this work we have developed high quality hydrogenated amorphous silicon (a-Si:H) for various nano-photonic applications, and successfully demonstrated a vertically-stacked, amorphous silicon micro-ring resonators on c-Si photonic nanowire using SU-8 polymer interlayer. In addition the developed a-Si:H has comparable refractive index (~3.6 at 1550 nm), and wider transmission window from 700 nm up to 10 microns compared to c-Si. This leads to the demonstration of various nano-photonic devices in wide spectral range, including (1) angle tolerant colour filters, and a-Si:H metasurface for subtractive colouring; (2) ultrafast all-optical switch using two photon absorption of nano-resonators, micro-lens array in near-infrared (IR) band utilising conformal deposition of a-Si:H films, and an integration platform for 2D materials, for instance MoSe₂ for enhanced second-harmonic generation; (3) a-Si:H meta-lens at mid-infrared, and chemical sensors for proteins.