Thin-Film Photodetectors for Infrared Multispectral Imaging

In recent years, there is a significant increase in the integration of infrared image sensors in many everyday use devices such as smartphones and laptops, driven by the need for biometric sensors such as face recognition and fingerprint scanners. At the same time, a variety of new applications such as self-driving cars augmented reality (AR), virtual reality (VR) can take advantage of developments in infrared imaging technology. Specifically, a growing demand exists for sensing technologies in the short-wave-infrared (SWIR), which relates to wavelengths in the range of 1-2 µm. Nowadays, the available technologies for IR sensors are rather limited. Silicon can only detect in the near-infrared range (NIR) with a strong cut-off after 900 nm and the III-V semiconductors that are used for the SWIR spectrum are having constraints in terms of throughput, resolution, and high cost.

Colloidal quantum dots (QDs) offer an alternative approach in detecting infrared light. Taking advantage of the quantum confinement, QDs can be tuned to detect different spectra from visible up to the NIR and SWIR. Furthermore, they can be deposited from solution over large areas with low-cost techniques such as spin coating. Integration of colloidal QDs on CMOS chips has been successfully demonstrated and commercial products are already available on the market, competing with traditional III-V semiconductor-based products. The present solutions are based on a thin-film photodiode with QDs as its absorber. Such a sensor captures signals in a broadband region of the IR spectrum, defined by the size of QDs deployed in the photodiode structure. The goal of this project is to exploit features of colloidal QDs such as solution-processability and size-dependent absorption to develop more complex device structures, capable of capturing signals at different bands of the IR spectrum. Having a low-cost image sensor that can operate in multiple IR bands would be attractive for many industrial applications.

The student will focus on the investigation of novel architectures for multispectral IR photosensors and their fabrication in wet chemical labs. Training on the relevant processing and characterization tools will be given and after a short introduction to the facilities, an independent investigation is expected with the focus on short-term research goals.