Photovoltaic Action With Broadband Photoresponsivity in Germanium-MoS2 Ultrathin Heterojunction

The heterostructures fabricated with a combination of 2-D materials and conventional semiconductors are of great interest owing to their unique optoelectronic properties. Here, we demonstrate the fabrication of a germanium (Ge)/MoS
₂
heterostructure and observation of a photovoltaic action with broadband photoresponsivity. A thin interface was formed in-between the thermally evaporated Ge and chemical vapor deposited MoS
₂
layers, considering the atomically smooth surface of MoS
₂
. The current density-voltage (J-V) measurement showed a diode like characteristic and photoresponsivity under light illumination. The Ge/MoS
₂
heterojunction showed an open circuit voltage (Voc) of 0.185V and short circuit current density (Jsc) of 0.028 mA/cm
₂
under illumination of light (wavelength 350-1100 nm). The transient photoresponse characteristics of the Ge-MoS
₂
heterojunction device showed significant photoresponsivity for ultraviolet, visible, and near-infrared light at different bias voltages. The interfacial charge transfer at the Ge-MoS
₂
heterojunction is the critical aspect to create an effective build in field for the broadband photoresponsive device. The demonstrated ultrathin heterojunction of Ge and MoS
₂
layers can be significant for developing self-powered broadband photodetectors.