Carrier conduction mechanisms of WSe₂/p-type Ge epilayer heterojunction depending on the measurement temperature and applied bias

We have fabricated a WSe₂/p-type Ge epilayer heterojunction and analyzed its electrical and carrier transport characteristics by temperature-dependent current–voltage (I–V) measurements in the range of 125–375 K. The WSe₂/p-type Ge heterojunction showed rectifying I-V characteristics at room temperature. The ideality factor and barrier height of the heterojunction were strongly dependent on temperature, which could be attributed to the inhomogeneous barrier height at the interface. Different current transport mechanisms were observed with the changes in temperature and applied bias. The thermionic emission mechanism governed the carrier transport at temperatures higher than 250 K, while at temperatures below 250 K, the carrier conduction was dominated by tunneling. The I–V curves at low temperatures showed a shift of carrier transport mechanism from direct tunneling at lower voltages to Fowler–Nordheim tunneling at higher voltages. The WSe₂/p-type Ge epilayer heterojunction exhibited a self-driven photo-switching property with a responsivity of 14.2 mAW⁻¹ and photo-current/dark-current ratio of ∼9 at a wavelength of 900 nm. The results show the potential of the two-dimensional transition-metal dichalcogenide/bulk semiconductor heterojunction devices for opto-electronic applications.