Fig. 1. Fabrication process of the device

Fig. 2. Test principle of the device

Fig. 3. Influence of dielectric layer thickness on device performance. (a) Dark current curve of the device; (b) spectral response curve of the device

Fig. 4. Raman spectra of graphene with different layers

Fig. 5. Influence of the number of graphene layers on the device performance. (a) Spectral response of the graphene under zero bias; (b) dark current of the graphene

Fig. 6. I-V curves of the device under different wavelengths of light

Fig. 7. Spectral response curves of Ge heterojunction and pure N-type Ge

Fig. 8. Responsivity of the device at different wavelengths

Fig. 9. Variation curves of device photocurrent and dark current with voltage

Fig. 10. Responsiveness of the device under different bias voltages

Fig. 11. Influence of excitation wavelength and bias voltage on device on/off ratio. (a) Influence of excitation wavelength on switching ratio; (b) influence of bias voltage on switching ratio

Fig. 12. NPDR of the device at different wavelengths

Fig. 13. Response time of the device

Fig. 14. Band diagram of the device without oxide layer between graphene and Ge

Fig. 15. Photoelectric response mechanism of the device. (a) Tunneling; (b) interface coupling