This special Physics department colloquium is scheduled for Wednesday 7/20/16 at 1:30 PM in the Kenwood Interdisciplinary Research Complex (KIRC) Room KEN 1150. Coffee and cookies will be available in KEN 3118 (third floor kitchenette located next to the elevators) at 3:30 PM. Anyone is welcome.

Spatial Inhomogeneous Barrier Heights at Graphene/Semiconductor Schottky Junctions
Dushyant Tomer, PhD Candidate/UWM Dept. of Physics

Graphene, a semimetal with linear energy dispersion, forms a Schottky junction when interfaced with a semiconductor. This dissertation presents temperature-dependent current-voltage and scanning tunneling microscopy/spectroscopy (STM/S) measurements performed on graphene Schottky junctions, formed with both two- and three-dimensional (2D and 3D) semiconductors.

To fabricate Schottky junctions, we transfer chemical vapor deposited monolayer graphene onto Si- and C-face SiC, Si, GaAs and MoS2 semiconducting substrates using a polymer assisted chemical method. We observe three main types of intrinsic spatial inhomogeneities: graphene ripples, ridges and semiconductor steps in STM imaging that can exist at graphene/semiconductor junctions. Tunneling spectroscopy measurements reveal fluctuations in the graphene Dirac point position, which is directly related to the Schottky barrier height. We find a direct correlation of the Dirac point variation with the topographic undulations of graphene ripples at the graphene/SiC junction. However, no such correlation is established at graphene/Si and Graphene/GaAs junctions and Dirac point variations are attributed to surface states and trapped charges at the interface.

We perform temperature dependent current-voltage measurements to investigate the impact of topographic inhomogeneities on electrical properties of the Schottky junctions. Additionally, we observe bias dependent current and barrier height in reverse bias regime also for all Schottky junctions.