Recent advances in two-dimensional p-type metal chalcogenides: synthesis, doping strategies and applications

Two-dimensional (2D) metal chalcogenides (MCs) showed great potential in meeting the requirements of high-performance (opto) electronic devices. In addition to the usual n-type MCs, developing p-type MCs is urgently demanded in preparing p-n junctions, bipolar junction transistors, field-effect transistors, etc. To this end, specified synthesis routes and engineering strategies for their key properties in (opto) electronics, including doping states, contact barriers and resistances, are critical to improving their performance. In the review, we summarize the recent advances in 2D p-type MCs by focusing on their direct synthesis routes, e.g. mechanical exfoliation, liquid exfoliation, chemical vapor deposition, and the p-type doping strategies, including substitutional doping, charge transfer doping and electrostatic doping. The corresponding applications in electronics and optoelectronics are also involved. Finally, the challenges and prospects of 2D p-type MCs are presented to provide a reference in this field.