Effect of Oxygen Adsorbates on Terahertz Emission Properties of Various Semiconductor Surfaces Covered with Graphene

Abstract

We have studied coherent terahertz (THz) emission from graphene-coated surfaces of three different semiconductors—InP, GaAs, and InAs—to provide insight into the influence of O2 adsorption on charge states and dynamics at the graphene/semiconductor interface. The amplitude of emitted THz radiation from graphene-coated InP was found to change significantly upon desorption of O2 molecules by thermal annealing, while THz emission from bare InP was nearly uninfluenced by O2 desorption. In contrast, the amount of change in the amplitude of emitted THz radiation due to O2 desorption was essentially the same for graphene-coated GaAs and bare GaAs. However, in InAs, neither graphene coating nor O2 adsorption/desorption affected the properties of its THz emission. These results can be explained in terms of the effects of adsorbed O2 molecules on the different THz generation mechanisms in these semiconductors. Furthermore, these observations suggest that THz emission from graphene-coated semiconductors can be used for probing surface chemical reactions (e.g., oxidation) as well as for developing O2 gas sensor devices.