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)/MoS2 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 MoS2 layers, considering the atomically smooth surface of MoS2. The current density-voltage (J-V) measurement showed a diode like characteristic and photoresponsivity under light illumination. The Ge/MoS2 heterojunction showed an open circuit voltage( V-oc)of 0.185 V and short circuit current density (J(sc)) of 0.028 mA/cm(2) under illumination of light (wavelength 350-1100 nm). The transient photoresponse characteristics of the Ge-MoS2 heterojunction device showed significant photoresponsivity for ultraviolet, visible, and near-infrared light at different bias voltages. The interfacial charge transfer at the Ge-MoS2 heterojunction is the critical aspect to create an effective build in field for the broadband photoresponsive device. The demonstrated ultrathin heterojunction of Ge and MoS2 layers can be significant for developing self-powered broadband photodetectors.