Photoelectric Measurements of the Modern Graphene-Insulator-Semiconductor (GIS) Test Structures

The fundamental property of any semiconductor device is its energy band diagram, which allows prediction of parameters and limitations of the device. The commonly used and most effective methods of band diagram determination are based on photoelectric measurements of specially prepared test structures, most often metal-insulator-semiconductor (MIS) capacitors. Such capacitors must have thin enough metal gates to make them semitransparent to light, which has to penetrate the gate and irradiate the substrate causing photoemission of carriers from both the gate and the substrate into the insulator. This way barrier heights (band offsets) on both sides of the insulator layer can be determined. In this paper we present the advantages of using in the photoelectric measurements the graphene-insulator-semiconductor (GIS) structures in which the metal gate is replaced by a graphene gate. Due to negligible thickness and high transparency of graphene photoelectric measurements allow determination of barrier heights for emission of both electrons and holes from the substrate into the insulator which allows direct determination of the insulator band gap. Using MIS structures it is practically impossible to measure the photocurrent due to hole emission from the substrate since it is overwhelmed by the large photocurrent due to electrons simultaneously emitted from the metal gate.