A technique that uses hydrogen to improve transistor performance on real-world graphene devices has been demonstrated on the wafer-scale by researchers in Penn State’s Electro-Optics Center (EOC). The researchers demonstrated a 3 times improvement in electron mobility of epitaxial graphene grown on the silicon face of a 100 mm silicon carbide wafer, as well as a similar improvement in radio-frequency transistor performance. Hydrogenation and device scaling gets us much closer to true high frequency performance.
We directly demonstrate the importance of buffer elimination at the graphene/SiC(0001) interface for high frequency applications. Upon successful buffer elimination, carrier mobility increases from an average of 800 cm2/(V s) to over 2000 cm2/(V s). Additionally, graphene transistor current saturation increases from 750 to over 1300 mA/mm, and transconductance improves from 175 mS/mm to over 400 mS. Finally, we report a 10× improvement in the extrinsic current gain response of graphene transistors with optimal extrinsic current–gain cutoff frequencies of 24 GHz.
We explore the effect of high-κ dielectric seed layer and overlayer on carrier transport in epitaxial graphene. We introduce a novel seeding technique for depositing dielectrics by atomic layer deposition that utilizes direct deposition of high-κ seed layers and can lead to an increase in Hall mobility up to 70% from as-grown. Additionally, high-κ seeded dielectrics are shown to produce superior transistor performance relative to low-κ seeded dielectrics and the presence of heterogeneous seed/overlayer structures is found to be detrimental to transistor performance, reducing effective mobility by 30–40%. The direct deposition of high-purity oxide seed represents the first robust method for the deposition of uniform atomic layer deposited dielectrics on epitaxial graphene that improves carrier transport.