Tunable negative photoconductivity in encapsulated ambipolar tellurene for functional optoelectronic device applications

Two-dimensional tellurium (2D Te) is a promising material for functional optoelectronic applications due to its narrow band gap and high carrier mobility. However, its light−matter interactions typically induce positive photoconductivity (PPC), leading to low photoresponsivity in 2D Te-based photodetectors due to their high dark current and the indirect 2D Te band gap. Here, we report novel tunable negative photoconductivity (NPC) in an Al2O3-encapsulated ambipolar 2D Te device, with excellent photoresponsivity of up to 6.9 × 104 A W−1, outperforming most previously reported 2D single-element chalcogen-based photodetectors. The NPC is attributed to the lower carrier mobility due to phonon scattering induced by the enhanced photothermal effect in the encapsulated Te layer. The threshold voltage can be tuned in the encapsulated 2D Te transistor under high-energy laser irradiation, demonstrating a new strategy for controlled 2D Te doping. Well-controlled gate-tunable negative and positive persistent photocurrents are achieved in the encapsulated 2D Te transistor, thus emulating biological synapse activity. An encapsulated 2D Te device with a flexible substrate also exhibits stable NPC after 1000 bending cycles, highlighting its potential use in wearable optoelectronic devices. The construction of ambipolar 2D Te phototransistors may pave the way for the development of novel functional optoelectronic devices.