Visible Phototransistors Based on Vertical Nanolayered Heterostructures of SnS/SnS₂ p–n and SnSe₂/SnS₂ n–n Nanoflakes

Two-dimensional (2D) nanomaterials have been attracting intensive interest due to their unique physical and optoelectronic properties. Van der Waals nanolayered heterostructures based on different 2D nanomaterials provide a state-of-the-art platform for investigating the physical phenomena and have extended the applications of 2D nanomaterials, leading to an era of next-generation high-performance electronic and optoelectronic technology. Herein, vertical 2D SnS/SnS2 p–n and SnSe2/SnS2 n–n nanolayered heterostructures are constructed by exfoliating individual materials and stacking them artificially. The two types of back-gate field-effect phototransistors show clear rectifying behaviors with the existence of band offset and excellent optoelectronic performances. The SnS/SnS2 p–n nanolayered heterostructure shows an ambipolar behavior with a hole mobility of 6.96 cm2·V–1·s–1 and electron mobility of 0.68 cm2·V–1·s–1, while the SnSe2/SnS2 n–n nanolayered heterostructure shows an intense n-type behavior with electron mobility of 3.78 cm2·V–1·s–1 and a high on/off ratio of over 105. Interestingly, due to the band alignments and built-in potentials in the two types of nanolayered heterostructures, the phototransistors exhibit enhanced responsive performances to illuminations of three-primary-color lasers (λ = 405, 532, and 650 nm) compared to the individual components. The SnS/SnS2 phototransistor shows a high photoresponsivity of 3567 A W–1, a high detectivity of 3.64 × 1013 Jones, and a fast response time of 0.8 ms. The SnSe2/SnS2 phototransistor also exhibits a high photoresponsivity of 1793 A W–1 and a fast response time of 15.4 ms.