| A novel mid-IR waveguide structure is used in sensing applications. (Image: Goran Mashanovich) |
A new research project led by a group at the University of Southampton's Optoelectronics Research Centre (Southampton, England) is aiming to establish whether germanium (Ge), a group IV semiconductor, can be used as the material of choice in mid-infrared (mid-IR) photonics circuits and sensors.
Mid-IR group IV photonics are used in chemical and biological sensing, environmental and hazardous substance monitoring, medicine, telecommunications, astronomy, and defense and security. So far, research in mid-IR group IV photonics has focused on silicon (Si)-based devices for shorter wavelengths due to its availability, low cost, maturity of fabrication processes, possibility for photonics-electronics integration, and good transparency.
Germanium's advantages
However, the transparency of Si only extends up to 8 μm and is therefore not very suitable as a core material for the mid-IR fingerprint band (8-14 μm). The Mid-Infrared GeRmAnium phoTonIcs fOr sensing (MIGRATION) project will investigate Ge as an alternative platform to Si with the aim to future-proof emerging technologies in this field. Compared to Si, Ge offers a number of other advantages in terms of device development, such as higher nonlinear coefficients, better carrier mobility, and the potential to produce active devices based on Ge-based alloys.
ORC Principal investigator Goran Mashanovich notes that the Southampton facilities include a £120 million cleanroom complex and 94 photonics laboratories. Mashanovich says the program will be closely connected with other very recently awarded research projects he is involved in that investigate near-IR and mid-IR silicon photonics circuits, including Si for telecommunication (such as "Silicon Photonics for Future Systems," an Engineering and Physical Sciences Research Council, or EPSRC, program grant) and sensing applications (such as"Mid-IR silicon photonics sources, detectors and sensors," funded by the Royal Society).
Developing high-quality Ge substrates
One of the main outcomes of the project will be to identify high-quality Ge substrates that rival the performance of the well-established Si-on-insulator wafers. This framework will then be used to demonstrate a library of devices such as waveguides, couplers, filters, amplifiers, and modulators that will form the building blocks of integrated on-chip circuits, systems, and sensors that operate over an wide wavelength span.
The project is funded by the EPSRC and will be led by Mashanovich and colleagues from ORC and elsewhere in the University of Southampton. The main project adviser will be Richard Soref from the University of Massachusetts (Amherst, MA), who pioneered silicon photonics and mid-IR group IV photonics, and other partners including several universities, the UK's Defence Science and Technology Laboratory, and IQE Silicon Compounds Ltd. (Cardiff, Wales).