Photonics at Interface: Heterogeneous Integrations for Generation, Detection, Conversion and Modulation

We will develop novel photonic devices by bonding two different semiconductor substrates with different spacing between atoms. It was very difficult to ensure an excellent quality at the interface, because the atoms cannot connect perfectly, if the lattice spacing is different. We will overcome this problem by making nano-scale tiny trenches to allow atoms to expand for releasing the strain accumulated at the interface. The quality of the interface is very important to make sure to reduce defects in the atomic scale. We will use the interface for making a highly sensitive detector to identify even just single photon (quantum of light), which is impossible to realise with defects due to the noise from additional carriers created by defects. This detector will be useful for future quantum technologies to enable secure communications and powerful commutations. We will also develop a novel laser and high speed optical switches by using this interface. Our project is summarised as follows: 1. Novel Manufacturing Technologies for Enabling Heterogeneous Integrations: We will develop new wafer-scale bonding process technologies to allow excellent interface qualities without defects. Our challenges to overcome the difference of lattice constants and thermal expansion constants for bonded materials. We will accumulate comprehensive knowledge for new bonding techniques. 2. Si/Ge Avalanche-Photo-Diodes and Si/Ge Lasers: The strain engineered interface will enable us to reduce dark currents of Si/Ge Avalanche-Photo-Diodes (APDs) to the level useful for detecting single photons at room temperature. Si/Ge APDs are also useful for LiDAR (Laser Imaging Detection and Ranging). The improved interface quality also enables to achieve lasing of Ge on a Si substrate towards monolithic integrations. 3. Si/LiNbO3 Hybrid Optical Modulator and Second-Harmonic-Generators: We will also bond LiNbO3 on a Si substrate, which allows us to utilise the electro-optic and nonlinear effects of LiNbO3, while keeping the advantages of nanoscale patterning of Si. The hybrid optical modulator with a slot waveguide will be operated at attojoule power consumption by removing the 50 Ohm-termination. The hybrid Second-Harmonic-Generators (SHGs) will convert various wavelengths to generate green and UV lights for much denser data-writing on DVDs. We think our approach will establish a new way of making heterogeneous interface with improved quality. Wafer-scale bonding of a patterned substrate is certainly well-known, but the nano-scale patterning to form perfect bonding in atomic-scale has not yet been achieved, yet. We will accumulate comprehensive knowledge on the developed interface, in terms of various physical parameters such as strains, voids, adhesions, and defects for researchers in nanoelectronics and photonics.