Electro-modulation and surface photovoltage spectroscopy with semi-transparent graphene electrodes

Abstract

Investigating the fundamental properties of new semiconductor materials and structures requires the use of a wide range of optical spectroscopy techniques. Among them, there are those that exploit the use of electrodes that are semi-transparent to light, a requirement arising from the need to either apply external perturbation to the studied material or sense the effects generated by light excitation. In this work, semi-transparent graphene electrodes were obtained by chemical vapour deposition of the graphene on a copper substrate and transferring these layers to a sapphire substrate. The fabricated electrodes were tested in contactless electroreflectance, soft-contact electroreflectance, and surface photovoltage spectroscopy on III-V epilayers (InP and GaAs) and van der Waals crystals (MoS2 and WSe2), reference industry-standard and emerging semiconductors. The obtained results clearly show that graphene electrodes are suitable for these measurements and have many advantages over the commonly used approaches to ensure transparent conducting layers in optoelectronic devices. On the other hand, compared to indium‑tin oxide, their transparency covers a wide spectral range, including ultraviolet (UV), revealing another important advantage. We also demonstrate that further structuring of the graphene layer enables maximizing the transparency up to the limit imposed by the hosting substrate.