Spatially separated bipolar transport and surface electron accumulation in tungsten diselenide nanostructures

Abstract

We investigated the physical origins of the bipolar transport in nanostructured and bulk WSe₂. A high electron concentration at the surface induced by surface electron accumulation (SEA) is confirmed by angle-resolved photoemission spectroscopy (ARPES) measurements. The n-type surface coexisting with the intrinsically p-doped inner bulk of WSe₂ results in an interesting “spatially separated” bipolar transport in this layered semiconductor. The selenium vacancies at the surface are inferred to be the major cause of SEA, and their formation and passivation are highly dependent on the interaction of ambient molecules. The maximum surface electron concentration, i.e., 10²⁰ cm⁻³, is approximately four orders of magnitude higher than the hole concentration of the inner bulk of WSe₂.