Controllable nondegenerate p-type doping of tungsten diselenide by octadecyltrichlorosilane

Despite heightened interest in 2D transition-metal dichalcogenide (TMD) doping methods for future layered semiconductor devices, most doping research is currently limited to molybdenum disulfide (MoS₂), which is generally used for n-channel 2D transistors. In addition, previously reported TMD doping techniques result in only high-level doping concentrations (degenerate) in which TMD materials behave as near-metallic layers. Here, we demonstrate a controllable nondegenerate p-type doping (p-doping) technique on tungsten diselenide (WSe₂) for p-channel 2D transistors by adjusting the concentration of octadecyltrichlorosilane (OTS). This p-doping phenomenon originates from the methyl (-CH₃) functional groups in OTS, which exhibit a positive pole and consequently reduce the electron carrier density in WSe₂. The controlled p-doping levels are between 2.1 × 10¹¹ and 5.2 × 10¹¹ cm^-2 in the nondegenerate regime, where the performance parameters of WSe₂-based electronic and optoelectronic devices can be properly designed or optimized (threshold voltage→, on-/off-currents→, field-effect mobility→, photoresponsivity, and detectivity as the doping level increases). The p-doping effect provided by OTS is sustained in ambient air for a long time showing small changes in the device performance (18-34% loss of ΔV_THinitially achieved by OTS doping for 60 h). Furthermore, performance degradation is almost completely recovered by additional thermal annealing at 120 °C. Through Raman spectroscopy and electrical/optical measurements, we have also confirmed that the OTS doping phenomenon is independent of the thickness of the WSe₂films. We expect that our controllable p-doping method will make it possible to successfully integrate future layered semiconductor devices.