Correlated lateral and vertical transport of large-scale majority carrier graphene–insulator–silicon photodiodes

Abstract

As the size of graphene–silicon (GS) or graphene–insulator–silicon (GIS) junction devices increases, both vertical and lateral transport behaviors interplay with each other. This study shows that the lateral transport behaviors of macroscopically large majority carrier GIS photodiodes affect the vertical transport properties and the performance of GIS photodiodes. The correlations between the lateral and vertical transport properties and the performance of large area GIS photodiodes are investigated by the electrode configuration dependent transport behavior and by the position dependent photoresponse. Lateral voltage drops occur due to resistive graphene layers. This causes the voltage across the junction of GIS devices along the vertical direction to vary with the distance from electrodes. As a result, the effective Schottky barrier height (SBH) governing the vertical transport behaviors also depends on the position and increases with the distance from electrodes. Due to the lateral potential distribution and the longer laterally transient time of photogenerated carriers along the graphene layer, the photoresponse becomes weaker as the distance increases from the electrodes. Graphene was doped and dedoped due to the employed functional PMMA overlayer. The PMMA overlayer acts as a promotion layer for a high photoresponse by capturing the tunneled photogenerated hot carriers from silicon. The correlation between the vertical and the lateral transport behaviors is analyzed based on the dark and photo current–voltage characteristics and the voltage dependent graphene Fermi level shift, which is also identified with Raman spectroscopy.