Studying Ambipolar Tellurene Field Effect Transistors using Microwave Near-Field Microscopy

The successful development of nanoscale semiconducting devices requires precise control over adjoining regions of n- and p-type transport. Key challenges remain the development of new materials with bipolar transport as desired for homojunction devices as well as techniques capable of studying local variations in carrier type and associated conductivity with nanometer spatial resolution. Here we image local electronic variations in ambipolar field effect transistors made from 2D films (tellurene) of the 1D van der Waals material tellurium using near-field scanning microwave microscopy (SMM). We perform SMM imaging together with differential measurements to study spatial variations in both carrier type and the associated conductivity as a function of the applied global backgate voltage. We produce nanometer resolved maps of the local carrier equivalence backgate voltage and show that the apparent device conductivity minimum determined from transport measurements in fact arises from the local coexistence of p- and n-type regions.