This project aims to develop a novel sensor concept for near-infrared (NIR) imaging and gamma-ray (x-ray) detection that leads to significant increase in the device performance in terms of sensitivity, accuracy and cost efficiency with respect to current technologies. As a starting point we have recently confirmed superior characteristics in UV radiation detection using specific light trapping nanostructures combined with defect-free junction formation with silicon. Here we study if similar approaches could be applied to germanium substrates, which would considerably widen the usable application range.
The successful implementation of our first idea requires fundamental material research as we plan to apply a specific nanotexturing process to germanium surfaces resulting in a graded efractive-index as well as extension of the optical path length inside the substrate. These eliminate the need for separate antireflection coating and thus provide superior optical properties. The second idea is to apply a highly charged conformal thin metal oxide on top of the nanostructures using atomic layer deposition (ALD). This brings two-fold benefit as compared to state-of-the art. First, it enables high-quality interface between germanium and surface oxide resulting in superior surface passivation properties as compared to conventionally used chemical vapour deposited silicon nitride.
Secondly, due to high fixed charge present in the ALD oxide, it can be used directly for high-quality pn-junction formation via induced junction. Thus, there is no need for ion implantation and subsequent annealing because there is no implantation induced damage in the junction. Since ALD films by nature grow on all exposed surfaces during single deposition, the benefit is expected to be groundbreaking in high-purity 3-dimensional coaxial detectors based on high purity germanium (HPGe) single crystals that are currently relying on complex ion implantation and annealing procedures.
At the end of the project, we should have deep understanding of the underlying physical mechanisms on light matter interactions in germanium nanostructures combined with convincing results on the new sensor concept with external quantum efficiency close or above unity up to 1800 nm wavelengths (NIR). Additionally, we should have demonstrated the potential for high quality HPGe-based x-ray (~ a few keV) and gamma-ray (30 keV-1MeV) sensors with reduced manufacturing costs.
In order to be able to bring the concept to the production within the next decade, we plan to demonstrate the applicability of the new sensor concept in nuclear safety and security applications in collaboration with the top industrial partners in the field. They are able to benchmark the novel ideas against the state of the art technology currently in production. In addition to the selected application areas, the results are likely to attract also other application areas such as medical technology, broadening the societal impact also to e.g. health & wellbeing.