PhD thesis supervisor: dr. Audrius Drabavičius (apply for recommendation)
Germanium sulfide thin films for low-voltage photosensors
Photodetectors are a crucial component of biomedical diagnostics, yet suitable solutions for portable devices are still lacking. Traditionally, bulky, high-voltage (>1000 V) photomultiplier tubes (PMTs) are used to register weak chemiluminescence signals (picowatts/nanowatts), while the most developed technology—silicon diodes—fundamentally lacks internal gain. The objective of this doctoral project is to bridge this technological gap by developing Germanium Sulfide (GeS) thin-film phototransistors that achieve PMT-level sensitivity with a low operating voltage suitable for batteries (<5 V). Unlike the samples based on exfoliated crystals most common in the literature, we will use rapid thermal evaporation (RTE) to form large-area coatings. The scientific novelty lies in the transition from passive photoconductors to field-effect transistor (FET) architecture, utilizing boron and phosphorus doping to modify electrical properties. Although doping typically increases conductivity, we will strategically use it to reduce contact resistance, enabling effective channel depletion and noise reduction. This would allow for higher sensitivity without the need for high voltage, paving the way for next-generation portable diagnostic devices.