Momentum-Direct\nInfrared Interlayer Exciton and Photodetection\nin Multilayer van der Waals Heterostructures

Interlayer\nexcitons (IX), spatially separated electron–hole\npair quasiparticles, can form in type-II van der Waals heterostructures\n(vdWH). To date, the most widely studied IX in hetero- and homobilayer\ntransition metal dichalcogenides feature momentum-indirect and visible\ninterlayer recombinations. However, momentum-direct IX emissions and\ninterlayer absorptions, especially in the infrared, are crucial for\nexcitonic devices but remain underexplored. In this work, we propose\nand construct a multilayer WSe<sub>2</sub>/InSe vdWH that hosts momentum-direct\nIX and manifests near-infrared interlayer absorptions at room temperature,\nverified by first-principles density functional theory calculations.\nWe conduct power- and temperature-dependent photoluminescence spectroscopies\nand extract the IX binding energy to be 43 ± 5 meV. Furthermore,\nwe manipulate the IX emission electrically via the Stark effect and\ntune its energy by 180 meV. Taking advantage of the direct interlayer\nabsorption, we fabricate a near-infrared vdWH photodetector modulated\nby strong photogating effect, and achieve the optimal photoresponsivity,\nspecific detectivity, and response time of 33 A W<sup>–1</sup>, 1.8 × 10<sup>10</sup> Jones, and 3.7 μs at 1150 nm.\nIn addition, we test the imaging capability of the photodetector by\nintegrating it into a single-pixel imaging system. Our work showcases\nthe possibility for constructing infrared-responsive vdWH that hosts\nmomentum-direct IX for future excitonic devices of optoelectronic\napplications.