Broad spectral photosensitivity from visible to shortwave infrared enhanced by annealing the heterojunction of germanium nanoparticles embedded in a silicon nitride layer on silicon

The structural, optical, and optoelectronic properties of germanium nanoparticles (Ge-NPs) in a silicon nitride (Si3N4) are studied for applications across the visible to short-wave infrared range (VIS-SWIR). Ge-NPs:Si3N4 films with a 70:30 volume ratio have been fabricated by magnetron sputtering on c-Si substrate and subsequently nanostructured by rapid thermal annealing (RTA) at 700°C, 750°C, and 800°C. A comprehensive characterization using Electron Microscopy, X-ray diffraction, Raman spectroscopy, optical absorption, and optoelectrical measurements revealed a strong dependence of the film properties on annealing temperature. At 700°C, Ge remains largely disordered, contributing to broad spectral sensitivity exceeding 1800nm and yielding the highest photocurrent-to-dark-current ratio, Jphoto/Jdark > 4200 at 100K, controlled by defect-related trap states at the Ge-NPs:Si3N4 interface. With increasing annealing temperature, Ge-NPs crystallize and grow, at 800°C, forming interconnected Ge domains with same crystalline orientation, accompanied by an optical bandgap widening (from 0.78eV to 0.83eV) and a photocurrent cutoff blue-shift (from ~1610nm to ~1370nm). The films annealed at 800°C exhibit a maximum responsivity of 9.2A/W at 100K, due to improved crystallinity and reduced defect density. These results highlight the tunabillity of VIS–SWIR optoelectronic performance in Ge-NPs:Si3N4 nanocomposites via controlled annealing, enabling optimization of light sensing mechanisms through defect engineering and structural tailoring.