Analysis of <i>p</i>-Type Doping in Graphene Induced by Monolayer-Oxidized TMDs

Abstract

Doping is one of the most difficult technological challenges for realizing reliable two-dimensional (2D) material-based semiconductor devices, arising from their ultrathinness. Here, we systematically investigate the impact of different types of nonstoichiometric solid MO_x (M are W or Mo) dopants obtained by oxidizing transition metal dichalcogenides (TMDs: WSe₂ or MoS₂) formed on graphene FETs, which results in <i>p</i>-type doping along with disorders. From the results obtained in this study, we were able to suggest an analytical technique to optimize the optimal UV-ozone (UVO) treatment to achieve high <i>p</i>-type doping concentration in graphene FETs (∼2.5 × 10¹³ cm^-2 in this study) without generating defects, mainly by analyzing the time dependency of <i>D</i> and <i>D</i>' peaks measured by Raman spectroscopy. Furthermore, an analysis of the structure of graphene sheets using TEM indicates that WO_x plays a better protective role in graphene, compared to MoO_x, suggesting that WO_x is more effective for preventing the degradation of graphene during UVO treatment. To enhance the practical application aspect of our work, we have fabricated a graphene photodetector by selectively doping the graphene through oxidized TMDs, creating a <i>p</i>-<i>n</i> junction, which resulted in improved photoresponsivity compared to the intrinsic graphene device. Our results offer a practical guideline for the utilization of surface charge transfer doping of graphene toward CMOS applications.