EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Information and communication technology has become ubiquitous in everyday life. Emerging distributed computing paradigms such as the Internet of Things are demanding the implementation of novel electronic device functionalities that go beyond the capabilities of conventional field effect transistors. In this context, nanometer scale Ge departs from its bulk counterpart and delivers unique electronic transport mechanisms that can be exploited at the device level. Thereto, a highly interesting transport mechanism is the transferred electron effect, enabling negative differential resistance (NDR). This effect is triggered by the application of high electric fields forcing a scattering of electrons from the energetically favorable conduction band valley, characterized by a low effective mass, to a heavy mass valley nearby. Despite a vast body of pioneering work, the practical use of NDR is still restricted to expensive GaAs and GaN semiconductors.
Here, we exploit the nanometer scale properties of Ge nanowires with unique monocrystalline Al contacts to deliver a strong and reproducible NDR effect at room temperature. Our monolithic Al-Ge-Al nanowire heterostructures embedded into field-effect transistor architectures are capable of combining doping-free Ge based electronics with an electrostatically tunable NDR. In this regard, we support our results with a detailed study of the key parameters of NDR. Most notably, we demonstrate a highly efficient and low-footprint platform paving the way for potential applications such as fast switching multi-valued logic devices, static memory cells, and high-frequency oscillators all implemented in one fully CMOS compatible Al-Ge based device platform. We believe that our investigations provide a significant step towards a beyond CMOS approach enabling functional diversification and alternative computing for the post-Si era by exploiting the unique band structure of nanometer scale Ge.