A high-frequency silicon-graphene-germanium barristor

Realising ubiquitous environmental monitoring and smart sensing devices compatible with Internet of Things (IoT) and 6 G networks requires transistors with terahertz (THz) cutoff frequencies (f_T) for efficient signal processing. However, the carrier transit time intrinsically limits conventional devices. Vertical two-dimensional (2D) base transistors offer a way to exceed this limit, yet interface losses typically suppress current gain, degrade high-frequency performance, and hinder THz operation. Here, we report a silicon-graphene-germanium barristor that overcomes these obstacles. Wafer-scale single-crystal graphene was epitaxially grown on germanium and integrated with silicon membranes, forming asymmetric Schottky barriers at the graphene-silicon and graphene-germanium interfaces. Using graphene's quantum capacitance, the asymmetric barriers enable distinct hot-carrier emission at both terminals and greatly increase the current gain, while graphene's atomic thickness minimises the perpendicular transit time. As a result, the device achieves a current gain up to 1.8 × 10⁷ and an intrinsic f_T up to 132 GHz, with modelling and simulation indicating scalability into the THz regime. These findings establish a promising high-frequency transistor paradigm for IoT sensors and systems.