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 (N ss ), 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 (R s ), 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.

Effect of Gadolinium on Electrical Properties of Polyethyleneimine Functionalized and Nitrogen‐Doped Graphene Quantum Dot Nanocomposite Based Diode

“…Norde's approach is also used to obtain ϕ B and R s values. [ 36 ] For this approach, the relationship in Equation () can be given as follows, $$$$\begin{equation}F\left( {{V}_{\mathrm{m}}} \right) = \frac{{{V}_{\mathrm{m}}}}{\gamma } - \frac{{kT}}{q}\left[ {\ln \left( {\frac{{I{V}_{\mathrm{m}}}}{{A{A}^*{T}^2}}} \right)} \right]\end{equation}$$$$where γ is an integer greater than the value of n obtained. ϕ B is described in the following way (Equation ) $$$$\begin{equation}{\phi }_{\mathrm{B}} = F\left( {{V}_m} \right) + \frac{{{V}_{\mathrm{m}}}}{\gamma } - \frac{{kT}}{q}\end{equation}$$$$…”

“…Hydrothermal synthesis of PEI@N‐GQDs successfully achieved. [ 31,35,36 ] Details of how to synthesize PEI@N‐GQDs are reported in our previous work. [ 35,36 ] The CA (3.60 g, 18.75 mmol) and PEI (2.34 g, 1.80 mmol) were dissolved in 50 mL of deionized distilled water.…”

“…[ 31,35,36 ] Details of how to synthesize PEI@N‐GQDs are reported in our previous work. [ 35,36 ] The CA (3.60 g, 18.75 mmol) and PEI (2.34 g, 1.80 mmol) were dissolved in 50 mL of deionized distilled water. The solution was incubated in an autoclave at 250 °C for 5 h. The suspensions were centrifuged at 12 000 rpm for 10 minutes, and the supernatant was collected after cooling to room temperature.…”

“…Details of the synthesis of N‐doped GQDs functionalized with PEI are included in our previous works. [ 35,36 ] The structure of the diode is shown in schematic form in Figure .…”

“…In our previous studies, [ 35,36 ] we investigated the I – V and C /( G/ω )– V properties of PEI functionalized and N‐doped GQDs without Gd at frequency range 1 kHz to 2 MHz in the voltage range of −3 to +7 V. The Gd‐free PEI@N‐GQDs sample showed the negative capacitance (NC) behavior at low frequencies. In this work, both the effect of gadolinium on the electrical properties of GdNPs/PEI@N‐GQDs‐based diode and surface states/trap levels characterizations were presented by the I – V and C /( G / ω )– V technique at 300 K in the frequency range of 0.5 to 500 kHz at ± 5 V.…”