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Öğe Effect of Gadolinium on Electrical Properties of Polyethyleneimine Functionalized and Nitrogen-Doped Graphene Quantum Dot Nanocomposite Based Diode(John Wiley and Sons Inc, 2023) Orhan, Elif; Anter, Aslıhan; Ulusoy, Murat; Polat, Barış; Okuyucu, Can; Yıldız, Mustafa; Altındal, ŞemsettinCarbon, especially graphene quantum dots (GQDs) based electronics have become an attractive technology in recent years. The controlled modification of the electrical and optoelectronic properties of GQDs by physical/chemical processes or synthetic methods may lead to new applications. Gadolinium-doped polyethyleneimine (PEI) functionalized and nitrogen-doped graphene quantum dots (GdNPs-PEI@N-GQDs) are synthesized by a hydrothermal method to determine how doping carbon-based materials with Gd alters the electrical properties of the structure. The electrical properties of the GdNPs/PEI@N-GQDs nanocomposite-based diode are investigated using the current–voltage (I–V) technique and the capacitance and conductance voltage (C–V & G/ω–V) technique at 300 K in the frequency range of 0.5 to 500 kHz at ± 5 V. The rectification ratio (RR) is found to be 14 at a voltage of ±5 V. The rectifying behavior of the diode changes to an ohmic behavior after doping with Gd, compared to the Gd-free PEI@N-GQDs sample (2.8 × 104 at ±5 V). The results are expected to have an impact on the understanding of carbon-based electronics technology.Öğe Electrical performance of a nanocomposite diode based on palladium nanoparticles- and polyethyleneimine functionalized nitrogen-doped graphene quantum dots(Nature Portfolio, 2025) Dikicioglu, Elanur; Efkere, Halil Ibrahim; Yildiz, Mustafa; Orhan, ElifA nanocomposite material comprising palladium nanoparticles (PdNPs) doped with polyethyleneimine (PEI)-functionalized nitrogen-doped graphene quantum dots (PEI N-GQDs) was synthesized and employed as an interlayer in an Ag/PdNPs/PEI N-GQDs/p-Si heterojunction configuration. The PdNPs/PEI N-GQDs nanocomposite was prepared through an aqueous reaction between PEI-functionalized N-GQDs and Pd(NO2)2H2O and characterized using FTIR, UV-Vis, TEM, XPS, and PL spectroscopy. The PL spectrum exhibited a broad emission centered at 580 nm (2.14 eV) with a near-infrared tail, indicating defect-assisted recombination and confirming the semiconducting nature of the nanocomposite. The Ag/PdNPs/PEI N-GQDs/p-Si diode displayed a rectification ratio of approximately 1.64 x 102 at +/- 4 V, with barrier heights of 0.87, 0.76, and 0.68 eV obtained from thermionic-emission (TE), Cheung, and Norde methods, respectively. Energy band alignment analysis revealed that the rectifying behavior originates from the Ag/nanocomposite interface, forming a Schottky-type barrier, while a type-II staggered junction is established at the nanocomposite/p-Si interface, facilitating hole transport. These findings demonstrate the potential of PdNPs/PEI N-GQDs as an effective interlayer material for carbon-based nanoelectronic and optoelectronic devices.Öğe Enhanced Rectification of Lanthanum Hydroxide-Doped Graphene Quantum Dots/Silicon Heterostructures at Cryogenic Temperatures(Wiley, 2025) Altan, Aslihan Anter; Berktas, Zeynep; Kaymak, Nuriye; Yildiz, Mustafa; Di Bartolomeo, Antonio; Orhan, ElifThis study reports the fabrication and temperature-dependent electrical characterization of a heterojunction formed by lanthanum(III) hydroxide nanoparticles doped with polyethyleneimine-functionalised nitrogen-doped graphene quantum dots (La(OH)3NPs/PEI N-GQDs) on n-type silicon (n-type Si). The heterostructure exhibits diode-like behaviour in the 77-400 K temperature range, with rectification exceeding two orders of magnitude and increasing as the temperature decreases, reaching an exceptionally high value above 10(5) at 77 K. Temperature-dependent diode parameters, including barrier height, series resistance, and ideality factor, are extracted using the thermionic emission model, revealing that barrier height increases and ideality factor decreases with rising temperature. These trends, along with significant deviations from the ideal Richardson behaviour of Schottky diodes, are effectively explained by the Werner-G & uuml;ttler model, which attributes them to Gaussian spatial inhomogeneities of the barrier arising from interface states and nanocomposite-induced fluctuations. This study highlights the robust rectifying behaviour, excellent cryogenic performance, and wide-temperature applicability of the La(OH)3NPs/PEI N-GQDs on the Si heterostructure, establishing it as a promising platform for low-power diode applications under extreme thermal conditions.Öğe High-Frequency Negative Capacitance in Graphene Quantum Dots/ Lanthanum(III) Hydroxide-based MIS Heterostructure(Elsevier, 2025) Anter, Aslıhan; Ulusoy, Murat; Polat, Barış; Yıldız, Mustafa; Di Bartolomeo, Antonio; Bi, Jinshun; Orhan, ElifLanthanides have significant potential for electronic technologies based on graphene quantum dots (GQDs), as they have unique electronic configurations characterized by 4f electrons. In this context, lanthanum(III) hydroxide nanoparticles (La(OH)3NPs) are used as dopants for polyethyleneimine (PEI)-doped nitrogen (N)-doped graphene quantum dots(PEIGQDsN) in this study. Using a novel green method, the La(OH)3NPs-doped PEI GQDs N nanocomposites are prepared from La(NO)3 in a single step and exploited as an interlayer in a metal/interlayer/ semiconductor (MIS) heterojunction with Au and n-Si. Capacitance & conductance-voltage (C-V & G/omega-V) characteristics of the Au/La(OH)3NPs doped PEI GQDs N /n-Si MIS heterojunction have been investigated as a function of frequency in the wide 500 Hz to 3 MHz range from-3 V to 5 V, at 300 K. It has been observed that the structure is highly sensitive to the frequency. In particular, at high frequencies, above 1.5 MHz, the positive capacitance (PC) transforms into a negative capacitance (NC) in forward bias. In addition, impedance measurements at high frequencies were carried out after the measurements in the dark, while the surface of the structure was illuminated at 100 mW/cm2. At the frequencies of 2 MHz and 3 MHz, where inductive behavior was observed, the light refilled the depleted trap levels, catalyzing the transition from NC to PC in forward bias. These findings suggest that the capacitance and conductance of the heterojunction have a remarkable frequency sensitivity, particularly evident at higher frequencies. The outcomes of this study are poised to significantly influence the comprehension of carbon-lanthanides-based electronic technology, and enable the creation of new hybrid functional materials for use in electronic or optoelectronic applications.Öğe Lanthanum(III)hydroxide Nanoparticles and Polyethyleneimine-Functionalized Graphene Quantum Dot Nanocomposites in Photosensitive Silicon Heterojunctions(Amer Chemical Soc, 2024) Anter, Aslıhan; Orhan, Elif; Ulusoy, Murat; Polat, Barış; Yıldız, Mustafa; Kumar, Arun; Di Bartolomeo, AntonioLanthanides are largely used in optoelectronics as dopants to enhance the physical and optical properties of semiconducting devices. In this study, lanthanum(III)hydroxide nanoparticles (La(OH)(3)NPs) are used as a dopant of polyethylenimine (PEI)-functionalized nitrogen (N)-doped graphene quantum dots ( (PEI-N)GQDs). The La(OH)(3) NPs-doped (PEI-N)GQDs nanocomposites are prepared from La(NO)(3) in a single step by a green novel method and are characterized by Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Deposited over an n-type Si wafer, the La(OH)(3) NPs-doped (PEI-N)GQDs nanocomposites form Schottky diodes. The I-V characteristics and the photoresponse of the diodes are investigated as a function of the illumination intensity in the range 0-110 mW cm(-2) and at room temperature. It is found that the rectification ratio and ideality factor of the diode decrease, while the Schottky barrier and series resistance increase with the enhancing illuminations. As a photodetector, the La(OH)(3) NPs-doped (PEI-N)GQDs/n-Si heterojunction exhibits an appreciable responsivity of 3.9 x 10(-3) AW(-1) under 22 mW cm(-2) at -0.3 V bias and a maximum detectivity of 8.7 x 10(8) Jones under 22 mW cm(-2) at -0.5 V. This study introduces the green synthesis and presents the structural, electrical, and optoelectronic properties of La(OH)(3) NPs-doped (PEI-N)GQDs, demonstrating that these nanocomposites can be promising for optoelectronic applications.Öğe Negative Capacitance Behavior at Low Frequencies of Nitrogen-Doped Polyethylenimine-Functionalized Graphene Quantum Dots-Based Structure(American Chemical Society, 2023) Berktaş, Zeynep; Orhan, Elif; Ulusoy, Murat; Yıldız, Mustafa; Altındal, ŞemsettinGraphene 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.
