Environmentally-friendly quantum dots
August 15, 2024
The new paper by the project coordinator ICFO focuses on the development of a novel method for synthesizing InSb/InP colloidal quantum dots stable under ambient conditions, an advance towards the expected results of the 2DNV project.
In their report of ACS Nano, they have employed these quantum dots to fabricate a fast and highly sensitive arsenic free shortwave infrared (SWIR) light sensor. The new strategy expands the possibility for the fabrication of optoelectronic devices based on environmentally friendly CQDs, compliant with the current regulations that limit their use in commercial consumer applications.
The SWIR light sensor industry has been dominated for years by the epitaxial technology, mainly based on devices made of indium gallium arsenide (InGaAs). However, several factors such as high production costs, low-scale manufacturability and incompatibility with CMOS has confined the epitaxial technology to niche and military markets.
While this recent CQDs is emerging as a competitor technology for InGaAs based devices, it is important to clarify that current CQDs based SWIR photodetectors use components such as lead (Pb) and mercury (Hg) chalcogenides. Both of these elements are subject to the Restriction of Hazardous Substances (RoHS) European directive, which regulates their usage in commercial consumer applications.
Therefore is a pressing urge for the development of SWIR light sensors based on environmentally friendly, heavy-metal-free CQDs.
In this new study published, they describe a new method to synthesize arsenic free InSb CQDs with access to the SWIR range. Their approach includes the design of an InSb/InP core-shell structure of the synthesized quantum dots that are used to fabricate a fast-response and highly-sensitive SWIR photodetector.
Lucheng Peng, ICFO researcher and first author of the study:
InSb/InP core-shell structure means growing another material (in this case, InP) on the surface of the pristine material (in this case, InSb). In comparison to InSb, InP is a wider bandgap material that can sufficiently passivate the surface traps of InSb that are detrimental in optoelectronic devices. Also, the Sb element is quite sensitive to oxygen, so the core-shell structure can largely improve the air stability of the material.
The team is now working on how to further reduce the dark current and increase the quantum efficiency of the CQDs based photosensors. In order to do so, they mainly need to focus on improving the carrier mobility in the thin films that contain the CQDs. Achieving this will allow them to get a faster response speed for the light sensor, aiming to go beyond the 10 ns response speed so that the technology can be used in i-ToF (indirect-time-of-flight), which is useful in LIDAR and 3D imaging.