Unveiling the origin of n -type doping of natural MoS 2 : carbon

MoS 2 has attracted intense interest in many applications. Natural MoS 2 and field-effect transistors made of it generally exhibit n -type characteristics, but its origin is unknown. Herein, we show that C is the origin of the universal n -type doping of natural MoS 2 . Photoemission spectroscopies reveal that while many MoS 2 samples with C detected are n -type, some without C exhibit p -type characteristics. The C-free, p -type MoS 2 changes to n -type over time with the concurrent appearance of C that is out-diffused from bulk, indicating that C induces the n -type doping. The C-origin is verified by C-deposition and supported by theoretical calculations. This carbon appears as nanometer-scale defects frequently observed in scanning tunneling microscopy. In addition, we propose, based on the calculations, that S vacancies are responsible for the p -type characteristics, which contrasts with the widespread belief. This work provides new perspectives on MoS 2 doping and presents a new direction for fabricating reliable MoS 2 devices.