Negative Capacitance Behavior at Low Frequencies of Nitrogen-Doped Polyethylenimine-Functionalized Graphene Quantum Dots-Based Structure

Abstract

Graphene quantum dots (GQDs), zero-dimensional members of the carbon family, have exceptional mechanical, thermal, and electrical properties. Nevertheless, pure GQDs have many challenges in reaching their full potential in electronic applications. Functionalizing or chemical modification of GQDs adjusts the physical and chemical properties, driving GQDs toward high-performance device applications. Nitrogen (N)-doped polyethylenimine (PEI) functionalized GQDs are capturing the interest of researchers specifically for electronic and photovoltaic applications these days. In this context, we present for the first time capacitance/conductance-voltage (C-V and G/ω-V) measurements of the nitrogen-doped PEI-functionalized GQDs-based structure for use in electronic applications in the frequency range from 1 kHz to 2 MHz at 300 K in this study. Capacitance features, the energy density distribution of surface states (Nss), and the relaxation time (τ) of a nitrogen-doped PEI-functionalized GQDs-based structure have been examined by using the admittance/conductance method. Negative capacitance (NC) behavior mostly exhibited by ferroelectric materials has been observed in the GQDs-based structure at low frequencies, and then it starts to disappear. NC is usually attributed to various surface states/interface traps, series resistance (Rs), and minority carrier injection. The NC phenomenon indicates that an increase in voltage gives rise to a decrease in the charge on the electrodes. The control of interfacial charges in such a heterostructure will be critical for NC devices. The results provide a basis for insights into semiconductor device technology.