Tunnel Epitaxy of III-V on Silicon for Ultralow Power Silicon Photonic Waveguide based Modulation Devices

High speed data communication underpins many important facets of modern life. High speed internet, online learning, high-definition video streaming, cloud computing, video conferencing, online gaming, artificial intelligence and the inner works of computers themselves all rely on the ability to transfer vast quantities of data at high speed. With the continuous introduction of increasing advanced and data hungry applications, the demand for bandwidth has grown relentlessly and is set to continue into the future. As data transmission rates increase so does power consumption and in some cases can dominate the power usage of the entire computing system. The growth of power use in the ICT industry is a major global concern with predictions showing that it could account for 20% of electricity usage worldwide and emit up to 5.5% of the world's carbon emissions by 2025. To support the growth in data demands it is of paramount importance that data communication technology is able to keep pace whilst minimising power use. Communication links are continuously being converted from working in the electrical domain to the optical domain since much more data can be transmitted optically with lower power consumption. The conversion is moving to progressively shorter links as the available technology becomes more cost effective and electrical bandiwdth limits are reached. Silicon photonic technology has been a key enabler of the conversion particularly in the data centre application space since the technology allows production of integrated photonics transceiver chips in a reliable, low-cost CMOS (Complementary metal-oxide-semiconductor) manner. Within the optical transmission link the process of converting electrical data into an optical format typically dominates power consumption. It is performed either by using an external optical modulator or by directly modulating the laser and for shorter optical links to be viable, their power usage must be reduced. For example, after almost two decades of research the performance of the silicon based optical modulator has manged to reach 100Gbaud with 1 pj/bit power consumption (including drive and tuning power), but power requirements for off chip and on chip links are ~100fJ/bit and 10fJ/bit respectively. For silicon photonic data transmission technology to meet these stringent energy and bandwidth requirements the hybrid integration of materials with stronger electro-optic effects onto silicon is essential as this will allow vast reductions in power consumption. In this proposal, we apply an advanced geometrically defined crystal growth process, tunnel epitaxy, to grow III-V semiconductors onto silicon photonic chips for use in a new-generation of optical modulation technology. The approach offers unique advantages in terms of footprint, yield, material quality and the ability to laterally grade doping levels during the growth process allowing precise optimisation of the trade-off between device bandwidth and optical loss. Combining the strength of the silicon photonics expertise at Southampton and the III-V on Si manufacturing at Cardiff, we will design and fabricate both external optical modulators and directly modulated light sources with state-of-the-art performance, targeting both short and ultra-short data reach applications. We will produce devices with 100Gbaud transmission with order of magnitude improvement in drive power which will enable the next generation of ultra short links to be viable. The developed technology will positively impact a large range of applications providing wide reaching societal and economic benefits.