A group of scientists led by professors Jürg Leuthold of the Institute for Electromagnetic Fields and Lukas Novotny of the Institute for Photonics, together with colleagues at the National Institute for Material Science in Tsukuba (Japan), have developed an extremely fast and sensitive light detector based on the interplay between novel two-dimensional materials and nano-photonic optical waveguides. Their results were recently published in the scientific journal Nature Nanotechnology.
"In our detector we wanted to exploit the advantages of different materials whilst overcoming their individual constraints," explains Nikolaus Flöry, a Ph.D. student in Novotny's group. "The best way of doing so is to fabricate a kind of artificial crystal—also known as heterostructure—from different layers that are each only a few atoms thick. Moreover, we were interested to know whether all the buzz about such two-dimensional materials for practical applications is actually justified."
In two-dimensional materials, such as graphene, electrons only move in a plane rather than three spatial dimensions. This profoundly alters their transport properties, for instance when an electrical voltage is applied. While graphene is not the ideal choice for optics applications, compounds of transition metals such as molybdenum or tungsten and chalcogenes such as sulfur or tellurium (abbreviated as TMDC) are highly photosensitive and, on top of that, can be easily combined with silicon optical waveguides.
The expertise for the waveguides and high-speed optoelectronics came from the research group of Jürg Leuthold. Ping Ma, the group's Senior Scientist, stresses that it was the interplay between the two approaches that made the new detector possible: "Understanding both the two-dimensional materials and the waveguides through which light is fed into the detector was of fundamental importance to our success. Together, we realized that two-dimensional materials are particularly suited to being combined with silicon waveguides. Our groups' specializations complemented each other perfectly."
[...] The ETH researchers are convinced that with this combination of waveguides and heterostructures they can make not just light detectors, but also other optical elements such as light modulators, LEDs and lasers. "The possibilities are almost limitless," Flöry and Ma enthuse about their discovery. "We just picked out the photodetector as an example of what can be done with this technology."
In the near future, the scientists want to use their findings and investigate other two-dimensional materials. About a hundred of them are known to date, which gives countless possible combinations for novel heterostructures. Moreover, they want to exploit other physical effects, such as plasmons, in order to improve the performance of their device even further.
More information: Nikolaus Flöry et al. Waveguide-integrated van der Waals heterostructure photodetector at telecom wavelengths with high speed and high responsivity, Nature Nanotechnology (2020). DOI: 10.1038/s41565-019-0602-z
