Epitaxial Growth of 2D Ternary Copper–Indium–Selenide Nanoflakes for High‐Performance Near‐Infrared Photodetectors

Abstract 2D semiconductors are promising for future photodetectors because of their dangling‐bond‐free surface, atomic thickness, tunable bandgap, high mobility, and flexible nature. However, the low light absorption is one of the main limits for the practical applications of 2D materials. Lots of efforts have been taken to optimize the light absorption, for example, constructing heterojunctions and exploring more photo‐sensitive 2D materials. Here, the epitaxial growth of layered copper–indium–selenide (CIS) nanoflakes is realized by chemical vapor deposition. The CIS nanoflakes are identified as β‐CuIn₅Se₈ with size of tens of micrometers and thickness in the range of 3.8 to 45 nm. The CIS nanoflakes show n‐type behavior with field effect mobility of up to 30.4 cm² V⁻¹ s⁻¹ and an on/off ratio of 10⁹. In addition, the CIS nanoflakes are ultra‐sensitive in the visible and near‐infrared region (450–1240 nm). They exhibit high photoresponsivity (1.6 × 10³ A W⁻¹), high external quantum efficiency (2.2 × 10⁵%), and high specific detectivity (5.3 × 10¹² Jones) irradiated by a 900‐nm laser. These performances are competitive among the current 2D materials, suggesting that this type of CIS shows potential for future near‐infrared photodetector applications.