Nano Photovolatics

One objective of this project is to study nanoscale electrical characteristics of graphene/silicon Schottky junctions. For this, Schottky-junction between CVD grown graphene and n-Si wafer have been formed and investigated using CAFM and KPFM techniques. The J-V characteristics of this device in dark and light conditions (100 mW/cm2) reveals photovoltaic response with open circuit voltage (VOC) of 0.3 V, short circuit current density (JSC) of 0.14 mA/cm2 and fill factor (FF) of 29%. The KPFM measurements were carried out under light conditions result 185mV and 160 mV VOC. This Voc difference is understood in terms of holes transfer to graphene resulting in the shift of Fermi level and the open circuit voltage variations at the junction.

Schematic representation of the two configurations used for KPFM measurements.
(a) Bias voltage is applied between graphene and top contact
(b) Bias is applied between Si (bottom contact) and graphene.
(c) VOC profile obtaining by subtracting surface potential image obtained under light condition.