Large-Area Tellurium/Germanium Heterojunction Grown by Molecular Beam Epitaxy for High-Performance Self-Powered Photodetector

As an attractive elemental semiconductor material, p-type tellurium (Te) with a narrow bandgap provides high carrier mobility, strong light–matter interactions in a wide spectral range, and good chemical stability, which enlightens the potential in optoelectronic devices. However, the applications are impeded by weak carrier separation and vague potential in scaling-up. In this work, the integration of Te and conventional semiconductor germanium (Ge) is designed. Through molecular beam epitaxy (MBE) method, large-area and uniform Te films with high crystallinity are directly deposited on the Ge substrates. The difference in work function between Te and Ge layer leads to a built-in electric field, which can effectively enhance the carrier separation. As a result, a self-powered splendid photovoltaic performance is observed in the MBE grown Te/Ge vertical heterojunction with current on/off ratio over 10³, responsivity (R) 523 mA W⁻¹, and specific detectivity (D*) 9.50 × 10¹⁰ cm Hz^1/2 W⁻¹ when illuminated by near-infrared light (980 nm, 2.15 µW cm⁻²). Furthermore, excellent stability and high response speed of the ultrathin heterostructure offer a significant application value for multipurpose photoelectric devices.