Metal Oxide Semiconductor / Graphene Heterojunction Based Sensors

Graphene, a two-dimensional material with very high carrier mobility, has drawn much attention for sensing chemical species. It is atomically thin hexagonal arrangement of carbon where each atom is attached to 3 neighboring carbon atoms. The presence of π* and π bonds can be attributed for it many remarkable properties. Some of these properties are high mobility, modulation of carrier concentration and Fermi level by electrical, optical, and chemical means, low 1/f and thermal noise, and very high surface to volume ratio to name a few making graphene a potential candidate for sensing material. However, to utilize these amazing properties for practical applications a reliable synthesis of high quality, large area graphene is needed. Chemical Vapor Deposition (CVD) based synthesis offers reliable, scalable, and inexpensive method to make low defect, continuous, large area, and thinner graphene with the ability to transfer graphene on any desirable substrate. In this work, high quality single layer graphene has been synthesized by CVD for sensing applications. The growth process was optimized to produce good quality monolayer graphene as characterized by Raman spectroscopy. CH4 has been used as precursor gas for the growth at 1035°C. Since graphene work function can be varied electrically or chemically, the Schottky Barrier Height (SBH) at Graphene/Semiconductor interface also varies accordingly affecting the carrier transport across the barrier. In this work, we used transition metal oxide (e.g. WO3, In2O3, and ZnO) along with graphene to study the behavior of graphene/metal oxide heterojunction in sensing NO2 and NH3 because both of these metal oxides and graphene are individually very sensitive to NO2 and NH3. Our motivation was to see if the sensitivity and response time improves in case we use them together