Hole Conduction of Tungsten Diselenide Crystalline Transistors by Niobium Dopant

Abstract

In spite of its ambipolar character, tungsten diselenide (WSe2) is known as one of a few p-type materials among transition metal dichalcogenides and is currently being used as a fundamental building block of homo- and hetero-junctions to meet the essential requirement of electronic devices. Many studies have solved the hole transport of WSe2 by contact engineering; however, another route is shown by an effective p-doping strategy for achieving reliable p-type transistor. Diverse characterization methods confirm the transition of the Fermi level from near midgap in intrinsic WSe2 to lower half bandgap with niobium substitutional doping, leading to a nondegenerate doping level exceeding a 10(17)-10(13) cm(-3) hole concentration. As a consequence, current on/off ratio and swing parameter have improved correspondingly as expected. The WSe2 transistors (with and without doping) are examined by the Zerbst-type method to conduct the transient data analysis enabling the systemic characterization of the generation lifetime and surface generation velocity of WSe2. It is demonstrated that the lifetime for WSe2 is commonly in the 0.5-0.1 mu gs range. The generation velocity is approximate to 10 000-fold slower than that of the typical crystalline silicon, which is attributed to the ultrathin body nature of the materials.