# Electrical Properties of ZnO Nanoparticle-Embedded/Polyethylenimine-Functionalized Nitrogen-Doped Graphene Quantum Dot Nanocomposites

## TL;DR

Researchers created a nanocomposite with zinc oxide nanoparticles and graphene quantum dots, which showed improved optoelectronic properties for potential use in silicon-based devices.

## Contribution

A novel ZnO nanoparticle and nitrogen-doped graphene quantum dot nanocomposite was synthesized and shown to enhance optoelectronic performance in diode configurations.

## Key findings

- The nanocomposite exhibited a direct optical band gap of ~3.0 eV and red-shifted visible emission at ~518 nm.
- The heterojunction diode showed enhanced photoresponse and reduced ideality factor compared to conventional diodes.
- The material formed a Schottky contact with a work function of ~3.17 eV and type-II-like band alignment.

## Abstract

In this work, a sustainable solution-based route was
employed to
synthesize a ZnONPs/PEI N-GQDs nanocomposite by integrating zinc oxide
nanoparticles into polyethylenimine-functionalized nitrogen-doped
graphene quantum dots. The primary optoelectronic properties of the
synthesized material in liquid phase were evaluated by UV–Vis
spectroscopy, and Tauc analysis indicated a direct optical band gap
of approximately 3.0 eV. Photoluminescence (PL) spectroscopy further
revealed a red-shifted visible emission centered at ∼518 nm,
attributed to defect- and interface-mediated radiative recombination
between ZnONPs and PEI-functionalized N-GQDs. Complementary structural
characterization using FTIR, XPS, and TEM confirmed the successful
formation of the hybrid nanocomposite, evidencing the coexistence
of ZnO nanoparticles and PEI-functionalized N-GQDs. Ultraviolet photoelectron
spectroscopy (UPS) was employed to elucidate the interfacial energy-level
alignment, yielding a work function of ∼3.17 eV and indicating
the formation of a Schottky contact at the metal/nanocomposite interface
together with a type-II-like band alignment at the ZnONPs/PEI N-GQDs/n-Si
junction. Two diode configurations were fabricated: a conventional
Au/n-type Si Schottky diode and a heterojunction diode based on Au/ZnONPs/PEI
N-GQDs/n-type Si. Their semilogarithmic current–voltage characteristics
were systematically investigated under dark and illuminated conditions
at room temperature. Compared with the Au/n-type Si reference, the
heterojunction diode exhibited pronounced rectification and a significantly
enhanced photoresponse. Illumination induced a substantial increase
in reverse current due to photogenerated carriers, resulting in a
decrease in the rectification ratio from 3.25 × 103 (dark) to 6.64 × 101 (light) at ±5 V, reflecting
a trade-off between rectification and photosensitivity. While the
Au/n-type Si diode showed a higher rectification ratio in the dark
(2.17 × 104 at ±5 V) and a lower ideality factor
(n = 5.06), the heterojunction device demonstrated
improved illuminated performance with a reduced ideality factor of
3.17 and an increased barrier height of 0.76 eV, underscoring its
potential for silicon-based optoelectronic applications.