The burgeoning need for extensive data processing has sparked enthusiasm for the development of a novel optical logic gate platform. In this study, junction field‐effect phototransistors based on molybdenum disulfide/Germanium (MoS₂/Ge) heterojunctions are constructed as optical logic units. This device demonstrates a positive photoresponse that is attributed to the photoconductivity effect occurring upon irradiation with visible (Vis) light. Under the illumination of near‐infrared (NIR) optics with wavelengths within the communication band, the device shows a negative photoresponse, which is associated with the interlayer Coulomb interactions. The current state of the device can be effectively modulated as different logical states by precisely tuning the wavelength and power density of the optical. Within a 3 × 3 MoS₂/Ge phototransistor array, five essentially all‐optical logic gates (“AND,” “OR,” “NAND,” “NOT,” and “NOR”) can be achieved in every signal unit. Furthermore, three complex all‐optical logical operations are demonstrated by integrating two MoS₂/Ge phototransistors in series. Compared to electronic designs, these all‐optical logic devices offer a significant reduction in transistor number, with savings of 50–94% when implementing the above‐mentioned functions. These results present opportunities for the development of photonic chips with low power consumption, high fidelity, and large volumes.

A sub-wavelength plasmonic Au–Ge grating was used to enhance the responsivity of Ge-based metal–semiconductor–metal photodetectors at infrared communication wavelengths. Furthermore, a finite-difference time-domain simulation was performed to optimize absorption of light by the detectors. Characterizations of the photoelectronic properties of the optimized device revealed high-performance photodetection with a responsivity of 0.38 A/W and an external quantum efficiency of 30% for 1.55 μm wavelength incident light. Moreover, an enhancement peak across three infrared telecommunication bands (C-band, L-band, and U-band) was achieved in the plasmon-enhanced photodetector. According to the simulation results of the optical absorption spectra, the distributions of electric field, and absorbed power, the enhancements of responsivity and quantum efficiency could be ascribed to the surface plasmons at the Au/Ge interface. These plasmons boosted inter-band transition and internal photoemission effect simultaneously, enabling high efficient photodetection around the C-band. The results of the fabricated devices demonstrated the potential of this approach for achieving high-performance Ge-based photodetectors.

Ge $_{{1}-{x}}$ Sn _x alloy films with Sn contents of 3% and 10% were grown on Si wafers by low-temperature nonequilibrium molecular beam epitaxy. The thermostabilities of the GeSn films and photodetectors containing them were studied. No Sn segregation was observed in Ge _0.97 Sn _0.03 films annealed below 750 °C. Conversely, Sn segregation occurred and Sn nanoparticles formed within the Ge _0.90 Sn _0.10 films annealed above 400 °C. Upon increasing the annealing temperature to 750 °C, Sn particles were thermally driven and segregated on the surface of both Ge _0.97 Sn _0.03 and Ge _0.90 Sn _0.10 films. Photodetectors were fabricated based on the as-grown and annealed Ge _0.90 Sn _0.10 films. Because of the decreased defect content of the Ge _0.90 Sn _0.10 film after annealing, the dark current of the GeSn photodetectors decreased obviously and the responsivity of the devices increased. These results are fundamentally important for the applications of high-performance photodetectors and lasers based on GeSn alloys.