Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors
Samuel Berweger, Gang Qiu, Yixiu Wang, Benjamin Pollard, Kristen L. Genter, Thomas M. Wallis, Wenzhuo Wu, Peide Ye, Pavel Kabos
Bipolar transport underpins a wide range of semiconductor homojunction device functionalities such as pn junctions or transistors. The capability to image and understand spatial inhomogeneities un carrier type and the conductivity associated with each carrier type in nanoscale ambipolar field effect transistors (FETs) and other bipolar devices has thus far proven elusive. Here we use microwave near- eld microscopy(SMM) to study ambipolar FETs of the 1D van der Waals material tellurene. We combine for the rst time the capability of SMM to image local variations in conductivity with differential SMM measurements study spatial variations in carrier type. Our measurements reveal strong spatial inhomogeneities in both conductivity and carrier type across individual devices, with signi cant p-doping at the edges and n-doping within the interior. We show that the device carrier equivalence point determined from transport measurements does not arise from uniform carrier neutrality, but rather from the continued coexistence of p- and n-type regions. Lastly, we produce nanometer resolved maps of the carrier equivalence backgate voltage, which directly addresses the need to image and understand spatial variations in carrier type in ambipolar FETs for the next generation of homojunction devices.