Dual-band plasmon-enhanced and bias-dependent responsivity in a flask-shaped Ge nanowire photodetector with Au grating

Special flask-shaped Au grating-Ge nanowire arrays are used to improve the performance of a Ge photodetector in the infrared optical communication band. The responsivity of the device with alternate Au grating-Ge nanowire arrays reaches as high as 0.75 and 0.62 A/W at 1310 and 1550 nm, respectively, indicating a nearly 100% increment compared to a device without a grating structure. This enhancement is attributed to the excitation of the surface plasmon polaritons, which simultaneously enhance the inter-band transition absorption and the internal photoemission of carriers. Moreover, the photoresponsivity of the dual-band plasmon-enhanced device is remarkably asymmetrical with regard to the voltage polarity, and the asymmetric ratios are about 4:1 and 3:1 at 1310 and 1550 nm, respectively. Band energy theory indicates that this bias-dependent responsivity originates from the asymmetrical distribution of hot electrons between the two electrodes and the mobility difference between electrons and holes in Ge. These results provide a valuable guideline for achieving a high performance dual-band near infrared photodetector, and the results demonstrate the potential of this approach for developing next-generation optoelectronic devices.