High-Performance Graphene-on-GaN Hot Electron Transistor

Hot electron transistors (HETs) are promising devices for high-frequency operation and probing the fundamental physics of hot electron transport. In a HET, carrier transport is out of plane due to the injection of hot electrons from an emitter to a collector which is modulated by a base electrode. HETs have been used to probe scattering events, band nonparabolicity, size-quantization effects, and intervalley transfer in different material systems. Monolayer graphene, being the thinnest available conductive membrane in nature, provides us with the opportunity to study the HET transport properties at the ultimate scaling limit.

Previously,wehavedemonstratedgraphene-base HET with GaN/AlN emitter and a graphene/WSe2 van der Waals heterostructure collector base-collector stack that can overcome the performance limitation of the graphene-base HETs with oxide barriers. In this work, we studied the effect of material parameters on the transport properties of the heterojunction diodes (i.e., Emitter-Base and Base-Collector) of HETs, and their impact on the HET performance. Temperature dependent transport measurements identify quantum mechanical tunneling as the major carrier transport mechanism in HETs. We demonstrate a new generation of graphene-base HET with record current density above kA/cm2 by scaling the tunneling barrier thickness and device geometry optimization. Preliminary simulations show that with further optimization graphene-on-GaN HET can outperform the bulk HETs towards ultra-high frequency operation.