Tuning the Doping of Epitaxial Graphene on a Conventional Semiconductor via Substrate Surface Reconstruction

Abstract

Combining scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we demonstrate how to tune the doping of epitaxial graphene from p to n by exploiting the structural changes that occur spontaneously on the Ge surface upon thermal annealing. Furthermore, using first principle calculations we build a model that successfully reproduces the experimental observations. Since the ability to modify graphene electronic properties is of fundamental importance when it comes to applications, our results provide an important contribution towards the integration of graphene with conventional semiconductors.

Tracking Interfacial Changes of Graphene/Ge(110) During In-Vacuum Annealing

“…The formation of the bubbles, confirming our previous report in Ref. [28], is concurrent with the appearance of the (6x2) reconstruction (β phase) on the Ge(110) surface. Indeed, the enlarged view reported in Fig.…”

“…Between 100 °C and 650 °C, this component is centered at 284.3 −0.03 +0.01 eV, while it shifts to 284.5 eV at 800 °C. The upshift could be possibly related to the decreased distance between graphene and Germanium in the γ phase after high-temperature annealing as well as to the n-doping of graphene observed in this phase [28].…”

“…Recent investigations have revealed a rich and complex scenario for the interface structure of graphene/Ge(110) [24][25][26][27][28]. As-grown CVD samples feature a hydrogen-passivated Ge surface (α phase) which is stabilized under the H2-rich growth conditions [11].…”

“…Above 350 °C, the Ge(110) surface starts to reconstruct forming a large (6x2) surface cell (β phase) [29], while, above 700 °C, a different reconstruction is formed which shares structural motifs of the (1x1) Ge termination (γ phase) [26,28]. The three phases may coexist on the Ge(110) surface under graphene at intermediate temperatures.…”

“…The phase transitions imply relevant changes in surface termination and an extensive rearrangement of Ge surface atoms; this is expected to affect the graphene layer above. For instance, it has been shown that the electronic properties of graphene are influenced by these structural changes occurring on the Ge(110) surface [28]. To date, however, little is known about if and how these structural modifications of the graphene/Ge(110) interface influence the quality of the graphene adlayer.…”