Two-dimensional hole gas in organic semiconductors

Abstract

A highly conductive metallic gas that is quantum mechanically confined at a solid-state interface is an ideal platform to explore non-trivial electronic states that are otherwise inaccessible in bulk materials. Although two-dimensional electron gases have been realized in conventional semiconductor interfaces, examples of two-dimensional hole gases, the counterpart to the two-dimensional electron gas, are still limited. Here we report the observation of a two-dimensional hole gas in solution-processed organic semiconductors in conjunction with an electric double layer using ionic liquids. A molecularly flat single crystal of high-mobility organic semiconductors serves as a defect-free interface that facilitates two-dimensional confinement of high-density holes. A remarkably low sheet resistance of 6\u2009kΩ and high hole-gas density of 1014\u2009cm−2 result in a metal–insulator transition at ambient pressure. The measured degenerate holes in the organic semiconductors provide an opportunity to tailor low-dimensional electronic states using molecularly engineered heterointerfaces. A two-dimensional hole gas with high carrier density is confined at the interface between a solution-processed, single-crystalline organic semiconducting film and the electric double layer formed by an ion gel on top of the film.