Fig. 1: Device architecture and material thicknesses.

a 3D schematic of the WSe2 phototransistor with middle (MG) and side gates (SG). The transparent blue layer is hBN on top of metal back gates on SiO2/Si and underneath WSe2 (channel material). The top layer in the green (‘Se’ atom) and black (‘W’ atom) ball-stick structure represents WSe2. b Optical microscope image of the device with MG and SGs defined at the bottom and S/D contacts on the top. c AFM scans indicate that the WSe2 channel is 7 nm thick and the hBN gate dielectric is 15 nm thick.