CMOS-compatible MBE-grown germanium quantum dots for high-performance photodetectors and solar cells

In this work, we grow and investigate CMOS-compatible Ge quantum dots (Ge QDs) integrated into metal–oxide–semiconductor (MOS) photodetectors, with a focus on their electrical transport and photocurrent response. Crystalline Ge QDs with an average diameter of ≈5.8 nm, hemispherical shape, and a high density (∼5 × 10 12 cm −2 ) are formed by solid-state dewetting of a 1 nm amorphous Ge film grown by molecular beam epitaxy (MBE) on SiO 2 /Si, subsequently capped with a 45 nm SiO 2 layer, and finally converted into MOS Ge-QD photodetectors by depositing transparent AuPd pads. Temperature-dependent current–voltage and capacitance–voltage measurements, complemented by photocurrent analysis, reveal the formation of a Schottky-like MOS photodetector exhibiting a rectification ratio close to 10 2 and a low dark current. Charge transport is governed by thermionic emission assisted by Fowler–Nordheim tunneling, with the embedded Ge QDs acting as efficient charge-relay centers in the oxide, facilitating carrier injection and reducing the threshold voltage without degrading the capacitive behavior of the structure. Under illumination, the Ge-QD–based MOS photodetectors show a pronounced enhancement of photosensitivity, particularly in the visible spectral range, consistent with strong quantum confinement in the QDs. These results demonstrate that MBE-grown Ge QDs obtained by solid-state dewetting provide a promising platform for the realization of CMOS-compatible, low-power, high-performance optoelectronic devices, especially photodetectors and, more broadly, quantum-dot–engineered solar-cell architectures.