Imaging conducting holes in field-effect transistors

Holes and electrons are indispensable charge carriers in various electronic and optoelectronic devices. However, holes are quasiparticles described as the absence of electrons, and their signals are often buried under strong electron-derived signals, making observation challenging. In this study, we propose a highly sensitive imaging method based on photoemission electron microscopy with a photon-energy-tunable laser source to visualize hole accumulation at the organic semiconductor–insulator interface in an organic field-effect transistor. By tuning the photon energy of the excitation source to the energy level corresponding to the top of the highest occupied molecular orbital, hole accumulation in an organic semiconductor could be detected as a decrease in photoemission intensity under an applied gate voltage. The proposed method has the potential to unveil the carrier transport mechanism in a wide range of semiconductor-based devices with real-time imaging of hole transport and accumulation. It thus paves the way for the development of state-of-the-art electronic devices.