Determination of Fermi Level Position at the Graphene/GaN Interface Using Electromodulation Spectroscopy

Graphene together with other 2D nanomaterials, due to their exceptional physiochemical properties, are often considered as excellent building blocks for fabrication of more complex heterostructures. Despite the processing-related issues the question of high importance for engineering of such systems is to fully understand the electronic phenomena at the interfaces. Electromodulation spectroscopy is extensively used in optical studies of semiconductors. Here, it is demonstrated that this nondestructive method may also be used to study the built-in electric fields in a complex graphene-semiconductor heterostructures, making it possible to precisely determine the potential barrier height at the interface and therefore to assess the electrical character of the junction. The study is focused on an especially interesting graphene-semiconductor pair, i.e., graphene/GaN nevertheless it can be applied to a broad diversity of heterostructures, particularly those consisting of van der Waals crystals. The results reveal that after deposition of a graphene the Fermi level is unpinned from native GaN surface states and, instead, located at a graphene/GaN interface characteristic energy.