Controllable Growth Orientation of SnS₂ Flakes for Low‐Noise, High‐Photoswitching Ratio, and Ultrafast Phototransistors

The planar semiconductor device fabrication techniques promote us to control the growth orientation of layered metal dichalcogenide materials. Herein, an efficient approach to control the growth orientation of tin disulfide flake (F‐SnS₂) and the applications in phototransistors is demonstrated. The in‐plane and vertical growth of F‐SnS₂ can be mediated by adopting different substrates. In‐plane, F‐SnS₂ is successfully grown on 2D substrates (mica, graphene, etc.) due to the van der Waals epitaxial growth. The vertical F‐SnS₂ grown on 3D substrates is attributed to the impeding effect of dangling bonds. The secondary growth control experiments are carried out and the growth results further verify our explanations. The in‐plane F‐SnS₂ is further applied in back‐gated phototransistors. The field‐effect mobility and current on/off ratio of back‐gated field‐effect transistors (BG‐FETs) reach 4 cm² V^‐1 s^‐1 and 10⁵. The as‐grown F‐SnS₂ phototransistors show small photoswitching ratio (≈1.3), large dark current (≈μA), and slow response time (≈second order). The sluggish response is ascribed to long‐lived traps which may be induced by sulfur vacancy defects (V _S). The as‐grown samples are further annealed in saturated sulfur atmosphere. The treatment can greatly suppress the deteriorating effect of long‐lived traps. The corresponding photoswitching ratio, dark current, and photoresponse time are improved to ≈40, pA order and millisecond order, respectively. The controllable orientation growth and efficient treatment technique are expected to be widely applied in other 2D metal dichalcogenide materials for high‐performance optoelectronic devices.