DOI: 10.1002/adma. 201600032 demonstrated the inverter circuit operation with complementary FETs fabricated on the same WSe 2 flake, where different contacts were formed (Pt/Au/Pd for p-FET and Au for n-FET). Another WSe 2 n-FET was achieved by Yu et al. through the low-work-function metal (Ag) contact and tetracyanoquinodimethane (F4tcnq) n-doping technique.[17] However, all researches currently remain at the level to accomplish simultaneously the different types of devices on one kind of TMDs. In particular, the performance of type-converted FET devices has not been clearly investigated in terms of optoelectronic devices.

Here, we report a high performance TMD photodetector with both a fast temporal photoresponse and a high responsivity that are in trade-off. This performance is achieved in a WSe 2-based FET fabricated on a hexagonal boron nitride (h-BN) layer by: i) converting the device type from a p-to n-channel and ii) precisely controlling the doping concentration of the WSe 2 layer through a triphenylphosphine (PPh 3)-based n-doping technique that is newly developed in this work. The phosphorus atoms in the PPh 3 molecules form lone pairs of electrons that enable the donation of electrons to the WSe 2 layer at level of 10 11 cm− 2. First, we discuss the controllability of PPh 3 n-doping on WSe 2 with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The effects of PPh 3 n-doping are then investigated on WSe 2-based FETs with different metal contacts (Ti and Pt) in terms of the performance of electronic (threshold voltage, oncurrent level, carrier concentration, and field-effect mobility) and optoelectronic (photoresponsivity and temporal photoresponse) devices. Finally, we further improve the photoresponsivity and temporal photoresponse performance of the PPh 3-doped WSe 2 photodetector by inserting the h-BN layer underneath the channel area and consequently suppressing the scattering phenomenon at the WSe 2/SiO 2 interface. First, we prepared three different PPh 3 concentration solutions (2.5, 5.0, and 7.5 wt%) and WSe 2 samples, which were mechanically exfoliated onto a SiO 2/Si substrate by scotch-tape in order to investigate the effects of PPh 3 doping on the WSe 2 by Raman spectroscopy and XPS analyses. As shown in Figure 1a, two conventional Raman peaks (E 1 2g and A 1g) were observed near 250 and 260 cm− 1 in the undoped WSe 2 sample (gray line), where the peaks indicate the in-and out-of-plane vibrations for bulk WSe 2, respectively.[18] The positions of the E 1 2g and A 1g Raman peaks were slightly blueshifted (dotted color lines) after performing the PPh 3 n-doping process on the WSe 2 films. We then extracted the peak shift values in each Raman peak before and after PPh 3 n-doping, and the values were plotted as a function of the PPh 3 concentrations in Figure 1 b. For each