Influence of composition on the external quantum efficiency of reduced graphene oxide/carbon nanoparticle based photodetector used for human body IR detection

Temperature dependence of electrical conductivity and variable hopping range mechanism on graphene oxide films

The rapid development of optoelectronic applications for optical-to-electrical conversion has increased the interest in graphene oxide material. Here, graphene oxide films (GOF) were used as source material in an infrared photodetector configuration and the temperature dependence of the electrical conductivity was studied. GOF were prepared by the double-thermal decomposition (DTD) method at 973 K, with a fixed carbonization temperature, in a pyrolysis system, under a controlled nitrogen atmosphere, over quartz substrates. Graphene oxide films were mechanically supported in a photodetector configuration on Bakelite substrates and electrically contacted with copper wires and high-purity silver paint. Morphological images from the GOF's surface were taken employing a scanning electron microscope and observed a homogeneous surface which favored the electrical contacts deposition. Vibrational characteristics were studied employing Raman spectroscopy and determined the typical graphene oxide bands. GOF were used to discuss the effect of temperature on the film's electrical conductivity. Current-voltage (I-V) curves were taken for several temperatures varying from 20 to 300 K and the electrical resistance values were obtained from 142.86 to 2.14 kΩ. The GOF electrical conductivity and bandgap energy (E_g) were calculated, and it was found that when increasing temperature, the electrical conductivity increased from 30.33 to 2023.97 S/m, similar to a semiconductor material, and E_g shows a nonlinear change from 0.33 to 0.12 eV, with the increasing temperature. Conduction mechanism was described mainly by three-dimensional variable range hopping (3D VRH). Additionally, measurements of voltage and electrical resistance, as a function of wavelength were considered, for a spectral range between 1300 and 3000 nm. It was evidenced that as the wavelength becomes longer, a greater number of free electrons are generated, which contributes to the electrical current. The external quantum efficiency (EQE) was determined for this proposed photodetector prototype, obtaining a value of 40%, similar to those reported for commercial semiconductor photodetectors. This study provides a groundwork for further development of graphene oxide films with high conductivity in large-scale preparation.

Liquid-Exfoliated 2D Materials for Optoelectronic Applications

Two-dimensional (2D) materials have attracted tremendous research attention in recent days due to their extraordinary and unique properties upon exfoliation from the bulk form, which are useful for many applications such as electronics, optoelectronics, catalysis, etc. Liquid exfoliation method of 2D materials offers a facile and low-cost route to produce large quantities of mono- and few-layer 2D nanosheets in a commercially viable way. Optoelectronic devices such as photodetectors fabricated from percolating networks of liquid-exfoliated 2D materials offer advantages compared to conventional devices, including low cost, less complicated process, and higher flexibility, making them more suitable for the next generation wearable devices. This review summarizes the recent progress on metal-semiconductor-metal (MSM) photodetectors fabricated from percolating network of 2D nanosheets obtained from liquid exfoliation methods. In addition, hybrids and mixtures with other photosensitive materials, such as quantum dots, nanowires, nanorods, etc. are also discussed. First, the various methods of liquid exfoliation of 2D materials, size selection methods, and photodetection mechanisms that are responsible for light detection in networks of 2D nanosheets are briefly reviewed. At the end, some potential strategies to further improve the performance the devices are proposed.

Variation of Optical Properties of Nitrogen-doped Graphene Quantum Dots with Short/Mid/Long-wave Ultraviolet for the Development of the UV Photodetector

Nitrogen-doped graphene quantum dots (NGQDs) synthesized from a single glucosamine precursor are utilized to develop a novel UV photodetector. Optical properties of NGQDs can be altered with short- (254 nm), mid- (302 nm), and long-wave (365 nm) ultraviolet (UV) exposure leading to the reduction of absorption from deep to mid UV (200-320 nm) and enhancement above 320 nm. Significant quenching of blue and near-IR fluorescence accompanied by the dramatic increase of green/yellow emission of UV-treated NGQDs can be used as a potential UV-sensing mechanism. These emission changes are attributed to the reduction of functional groups detected by Fourier transformed infrared spectroscopy and free-radical-driven polymerization of the NGQDs increasing their average size from 4.70 to 11.20 nm at 60 min treatment. Due to strong UV absorption and sensitivity to UV irradiation, NGQDs developed in this work are utilized to fabricate UV photodetectors. Tested under long-/mid-/short-wave UV, these devices show high photoresponsivity (up to 0.59 A/W) and excellent photodetectivity (up to 1.03 × 10¹¹ Jones) with highly characteristic wavelength-dependent reproducible response. This study suggests that the optical/structural properties of NGQDs can be controllably altered via different wavelength UV treatment leading us to fabricate NGQD-based novel UV photodetectors providing high responsivity and detectivity.