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3 pages, 168 KiB

Open AccessEditorial

Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices

by Siva Pratap Reddy Mallem

Crystals 2022, 12(1), 67; https://doi.org/10.3390/cryst12010067 - 4 Jan 2022

Cited by 1 | Viewed by 1127

Abstract

This Special Issue on “Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices” is a collection of 20 original articles dedicated to theoretical and experimental research works providing new insights and practical findings in the field of solid-state technology-related topics [...] Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

Research

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16 pages, 3567 KiB

Open AccessArticle

Electronic and Optical Properties of Polythiophene Molecules and Derivatives

by Huai-Wen Tsai, Kan-Lin Hsueh, Mei-Hsin Chen and Che-Wun Hong

Crystals 2021, 11(11), 1292; https://doi.org/10.3390/cryst11111292 - 25 Oct 2021

Cited by 15 | Viewed by 3078

Abstract

The electronic and optical properties of polythiophene (PT) for polymer light-emitting diodes (PLEDs) were calculated using density functional theory (DFT) and time-dependent DFT. We calculated the electronic and optical properties of thiophene and PT polymers with degrees of polymerization (DP) from 2 to [...] Read more.

The electronic and optical properties of polythiophene (PT) for polymer light-emitting diodes (PLEDs) were calculated using density functional theory (DFT) and time-dependent DFT. We calculated the electronic and optical properties of thiophene and PT polymers with degrees of polymerization (DP) from 2 to 30 monomers (T1–T30) and their derivatives. The associated highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy, band gaps, electron orbitals, and molecular structures were determined. As the DP increased, the LUMO energy gradually decreased, and the HOMO energy gradually increased. The band gap of PT approached 2 eV as the DP of the PT polymer increased from 1 to 30. The calculations and exchange–correlation functional were verified against values in the literature and experimental data from cyclic voltammetry (redox potential) and ultraviolet-visible, photoluminescence, and ultraviolet photoelectron spectra. The color of PT PLEDs can be adjusted by controlling the DP of the polymer and the substituents. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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13 pages, 8804 KiB

Open AccessArticle

Synthesis of Thermally Stable h-BN-CNT Hetero-Structures via Microwave Heating of Ethylene under Nickel, Iron, and Silver Catalysts

by Yahaya Saadu Itas, Chifu E. Ndikilar, Tasiu Zangina, Hafeez Yusuf Hafeez, A. A. Safana, Mayeen Uddin Khandaker, Pervaiz Ahmad, Ismail Abdullahi, Badmus Kausara Olawumi, Muhammad Auwal Babaji, Hamid Osman and Sultan Alamri

Crystals 2021, 11(9), 1097; https://doi.org/10.3390/cryst11091097 - 9 Sep 2021

Cited by 17 | Viewed by 2398

Abstract

Initially, three samples of carbon nanotubes (SWCNTs) were synthesized from neem tree material. Afterward, these samples were coated with hexagonal boron nitride (h-BN) to form h-BN and CNT composite (h-BN-CNT). The essence of using h-BN (being a [...] Read more.

Initially, three samples of carbon nanotubes (SWCNTs) were synthesized from neem tree material. Afterward, these samples were coated with hexagonal boron nitride (h-BN) to form h-BN and CNT composite (h-BN-CNT). The essence of using h-BN (being a perfect insulator) with armchair SWCNT (being a conductor) is to create an interface between an insulator and conductor. The samples were treated under three different transition metal nanoparticles; silver, iron, and nickel. Thermogravimetric (TGA) analysis reveals that h-BN/CNT is thermally more stable with silver than iron and nickel nanoparticles. TGA profile showed resistance to mass loss at the beginning due to the higher thermal resistivity by the impurity compounds. The DFT calculation, generalized gradient approximation (GGA), and Perdew–Burke–Ernzerhof (PBE) analysis found engineered bandgap energy of 3.4 eV for the synthesized h-BN-CNT heterostructure. Because of its unique structural and electronic properties such as tunable bandgaps, the h-BN-CNT heterostructure may open new ways for manipulating excitons in the CNTs, and thus can be explored to develop various new electronic devices. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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9 pages, 2780 KiB

Open AccessFeature PaperCommunication

Dynamic Performance Characterization Techniques in Gallium Nitride-Based Electronic Devices

by Carlo De Santi, Matteo Buffolo, Gaudenzio Meneghesso, Enrico Zanoni and Matteo Meneghini

Crystals 2021, 11(9), 1037; https://doi.org/10.3390/cryst11091037 - 28 Aug 2021

Cited by 6 | Viewed by 2034

Abstract

In this paper, we compare and discuss the main techniques for the analysis of the dynamic performance of GaN-based transistors. The pulsed current-voltage characterization provides information on the effect of different trapping voltages on various bias points of the device under test, leading [...] Read more.

In this paper, we compare and discuss the main techniques for the analysis of the dynamic performance of GaN-based transistors. The pulsed current-voltage characterization provides information on the effect of different trapping voltages on various bias points of the device under test, leading to the detection of all the possible effects, as well as to the choice of the optimal filling and measure bias conditions in other techniques. The drain current transients use one of the identified bias configurations to extract information on the deep level signature responsible for the performance variation and, thus, they can pinpoint the corresponding physical crystal lattice configuration, providing useful information to the growers on how the issue can be solved. Finally, given the complex interplay between the filling and emission time constants, the gate frequency sweeps can be used to obtain the real performance in the target operating condition. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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10 pages, 2929 KiB

Open AccessArticle

Optical Properties and Band Gap of Ternary PSN-PMN-PT Single Crystals

by Wei Long, Xing Fan, Pinyang Fang, Xiaojuan Li and Zengzhe Xi

Crystals 2021, 11(8), 955; https://doi.org/10.3390/cryst11080955 - 16 Aug 2021

Cited by 4 | Viewed by 2266

Abstract

This study investigated the optical properties and the interband transition of a ternary [100]-oriented 6PSN-61PMN-33PT relaxor ferroelectric single crystal. Compared with the binary [100]-oriented PMN-32PT crystal, the [100]-oriented 6PSN-61PMN-33PT crystal exhibited excellent optical properties, including high transmittance, low refractive index, weak frequency dispersion, [...] Read more.

This study investigated the optical properties and the interband transition of a ternary [100]-oriented 6PSN-61PMN-33PT relaxor ferroelectric single crystal. Compared with the binary [100]-oriented PMN-32PT crystal, the [100]-oriented 6PSN-61PMN-33PT crystal exhibited excellent optical properties, including high transmittance, low refractive index, weak frequency dispersion, and low reflection and absorption coefficients. All these differences can be attributed to the structural changes of the 6PSN-61PMN-33PT crystal, such as its large lattice size and increased band gap. The crystal’s transmittance was significantly improved after alternating current electric field poling due to the increased domain size and the order domain structure. The largest transmittance for the 6PSN-61PMN-33PT crystal was up to 66%. Our experimental results indicate that the ternary 6PSN-61PMN-33PT ferroelectric single crystal has great application potential in the optical field. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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16 pages, 4068 KiB

Open AccessArticle

Band-Gap Properties of Finite Locally Resonant Beam Suspended Periodically with Two-Degree-of-Freedom Force Type Resonators

by Hangyuan Lv, Shangjie Li, Xianzhen Huang and Zhongliang Yu

Crystals 2021, 11(6), 716; https://doi.org/10.3390/cryst11060716 - 21 Jun 2021

Cited by 7 | Viewed by 2397

Abstract

The propagation properties of waves in finite Timoshenko locally resonant (LR) beams resting on forced vibrations and periodically attached two-degree-of-freedom force-type resonators are studied by the wave-based analysis approach. By calculating the motion equations of the beam, the transmission and reflection matrices of [...] Read more.

The propagation properties of waves in finite Timoshenko locally resonant (LR) beams resting on forced vibrations and periodically attached two-degree-of-freedom force-type resonators are studied by the wave-based analysis approach. By calculating the motion equations of the beam, the transmission and reflection matrices of waves at the resonator attached point are first derived, and the forced vibration response of the finite periodic beam is deduced by the wave-based approach. Several examples are also analyzed by the finite element method to verify the high accuracy of the developed wave-based analysis approach. Numerical results show that wider low-frequency band-gaps exist in this type of LR beams. It was also found that the resonator masses and spring stiffnesses caused different effects on the band-gap properties of the combined LR beam. The desired band-gap widths of the LR beam can be tuned by adjusting the mass blocks and spring stiffness in the resonators based on the results. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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7 pages, 2600 KiB

Open AccessArticle

Improved Noise and Device Performances of AlGaN/GaN HEMTs with In Situ Silicon Carbon Nitride (SiCN) Cap Layer

by Yeo-Jin Choi, Jae-Hoon Lee, Jin-Seok Choi, Sung-Jin An, Young-Min Hwang, Jae-Seung Roh and Ki-Sik Im

Crystals 2021, 11(5), 489; https://doi.org/10.3390/cryst11050489 - 27 Apr 2021

Cited by 6 | Viewed by 2359

Abstract

We investigated the effects of in situ silicon carbon nitride (SiCN) cap layer of AlGaN/GaN high-electron mobility transistors (HEMTs) on DC, capacitance-voltage (C-V) and low-frequency noise (LFN). The proposed device with SiCN cap layer exhibited enhanced drain current, reduced gate leakage current, low [...] Read more.

We investigated the effects of in situ silicon carbon nitride (SiCN) cap layer of AlGaN/GaN high-electron mobility transistors (HEMTs) on DC, capacitance-voltage (C-V) and low-frequency noise (LFN). The proposed device with SiCN cap layer exhibited enhanced drain current, reduced gate leakage current, low interface trap density (D_it), and high on/off ratio thanks to the passivation effect, compared to the device without SiCN cap layer. Both devices clearly showed 1/f noise behavior with carrier number fluctuations (CNF), regardless of the existence of SiCN cap layer. The proposed device presented the relative low trap density (N_it) and reduced access noise due to the effective surface passivation in source-drain access region compared to the device without SiCN cap layer. From the improved DC, C-V and noise results of the proposed device, the in situ SiCN cap layer plays an important role in the passivation layer and gate oxide layer in AlGaN/GaN HEMT. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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9 pages, 19010 KiB

Open AccessArticle

Potato Chip-Like 0D Interconnected ZnCo₂O₄ Nanoparticles for High-Performance Supercapacitors

by Siva Pratap Reddy Mallem, Mallikarjuna Koduru, Kuppam Chandrasekhar, S. V. Prabhakar Vattikuti, Ravi Manne, V. Rajagopal Reddy and Jung-Hee Lee

Crystals 2021, 11(5), 469; https://doi.org/10.3390/cryst11050469 - 22 Apr 2021

Cited by 22 | Viewed by 3308

Abstract

Zinc cobaltite (ZnCo₂O₄) is an emerging electrode material for supercapacitors due to its rich redox reactions involving multiple oxidation states and different ions. In the present work, potato chip-like 0D interconnected ZnCo₂O₄ nanoparticles (PIZCON) were prepared [...] Read more.

Zinc cobaltite (ZnCo₂O₄) is an emerging electrode material for supercapacitors due to its rich redox reactions involving multiple oxidation states and different ions. In the present work, potato chip-like 0D interconnected ZnCo₂O₄ nanoparticles (PIZCON) were prepared using a solvothermal approach. The prepared material was characterized using various analytical methods, including X-ray powder diffraction and scanning electron microscopy. The possible formation mechanism of PIZCON was proposed. The PIZCON electrode material was systematically characterized for supercapacitor application. The areal capacitance of PIZCON was 14.52 mF cm⁻² at 10 µA cm⁻² of current density, and retention of initial capacitance was 95% at 250 µA cm⁻² following 3000 continuous charge/discharge cycles. The attained measures of electrochemical performance indicate that PIZCON is an excellent supercapacitor electrode material. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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11 pages, 4734 KiB

Open AccessArticle

Crystalline AlN Interfacial Layer on GaN Using Plasma-Enhanced Atomic Layer Deposition

by Il-Hwan Hwang, Myoung-Jin Kang, Ho-Young Cha and Kwang-Seok Seo

Crystals 2021, 11(4), 405; https://doi.org/10.3390/cryst11040405 - 10 Apr 2021

Cited by 6 | Viewed by 3514

Abstract

In this study, we report on the deposition of a highly crystalline AlN interfacial layer on GaN at 330 °C via plasma-enhanced atomic layer deposition (PEALD). Trimethylaluminum (TMA) and NH₃ plasma were used as the Al and N precursors, respectively. The crystallinity [...] Read more.

In this study, we report on the deposition of a highly crystalline AlN interfacial layer on GaN at 330 °C via plasma-enhanced atomic layer deposition (PEALD). Trimethylaluminum (TMA) and NH₃ plasma were used as the Al and N precursors, respectively. The crystallinity and mass density of AlN were examined using X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements, respectively, and the chemical bonding states and atomic concentrations of the AlN were determined by X-ray photoelectron spectroscopy (XPS). The AlN/n-GaN interface characteristics were analyzed using TOF-SIMS and STEM, and the electrical characteristics of the AlN were evaluated using metal-insulator-semiconductor (MIS) capacitors. The PEALD process exhibited high linearity between the AlN thickness and the number of cycles without any incubation period, as well as a low carbon impurity of less than 1% and high crystal quality even at a low deposition temperature of 330 °C. Moreover, the GaN surface oxidation was successfully suppressed by the AlN interfacial layer. Furthermore, enhanced electrical characteristics were achieved by the MIS capacitor with AlN compared to those achieved without AlN. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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6 pages, 1738 KiB

Open AccessArticle

Growth of High Quality GaN on Si (111) Substrate by Using Two-Step Growth Method for Vertical Power Devices Application

by Jae-Hoon Lee and Ki-Sik Im

Crystals 2021, 11(3), 234; https://doi.org/10.3390/cryst11030234 - 26 Feb 2021

Cited by 14 | Viewed by 4582

Abstract

A crack-free GaN film grown on 4-inch Si (111) substrate is proposed using two-step growth methods simply controlled by both III/V ratio and pressure. Two-step growth process is found to be effective in compensating the strong tensile stress in the GaN layer grown [...] Read more.

A crack-free GaN film grown on 4-inch Si (111) substrate is proposed using two-step growth methods simply controlled by both III/V ratio and pressure. Two-step growth process is found to be effective in compensating the strong tensile stress in the GaN layer grown on Si substrate. The high-resolution X-ray diffraction (XRD) rocking curves of (002) and (102) planes for the GaN epitaxial layer with two-step growth method are 317 and 432 arcsec, while the corresponding values for the reference sample without two-step growth method are 550 and 1207 arcsec, respectively. The reduced threading dislocation of GaN film with two-step growth method is obtained to be ~2 × 108/cm², which is attributed to effectively annihilate and bend threading dislocation. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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11 pages, 3178 KiB

Open AccessArticle

Green Synthesis of Reduced Graphene Oxide-Supported Palladium Nanoparticles by Coleus amboinicus and Its Enhanced Catalytic Efficiency and Antibacterial Activity

by Koduru Mallikarjuna, Lebaka Veeranjaneya Reddy, Sarah Al-Rasheed, Arifullah Mohammed, Sreedevi Gedi and Woo Kyoung Kim

Crystals 2021, 11(2), 134; https://doi.org/10.3390/cryst11020134 - 28 Jan 2021

Cited by 16 | Viewed by 3060

Abstract

Novel reduced graphene oxide-supported palladium nanoparticles (RGO-PN) were synthesized under ultrasonication, a method that utilizes Coleus amboinicus as a bio-reduction agent. Green synthesized RGO-PN nanoparticles with a crystallite size in the range of 40–50 nm were confirmed in X-ray diffraction (XRD) spectra. RGO-PN [...] Read more.

Novel reduced graphene oxide-supported palladium nanoparticles (RGO-PN) were synthesized under ultrasonication, a method that utilizes Coleus amboinicus as a bio-reduction agent. Green synthesized RGO-PN nanoparticles with a crystallite size in the range of 40–50 nm were confirmed in X-ray diffraction (XRD) spectra. RGO-PN show an absorption peak at 220 nm while reduced graphene oxide (RGO) shows its maximal absorbance at 210 nm. The scanning electron microscope image revealed that 40-nm-sized spherical-shaped palladium nanoparticles stick well to reduced graphene oxide sheets, which is consistent and correlated well with the XRD pattern. Moreover, a high-resolution morphological image of RGO-PN100 was obtained by TEM analysis, which shows the anchoring of palladium nanoparticles (PN) on RGO nanosheets. Green synthesized RGO-PN100 nanoparticles from Coleus amboinicus show better reduction kinetics for 4-nitrophenol at 40 min, suggesting that RGO-PN prepared from Coleus amboinicus serve as an excellent catalytic reducing agent. Furthermore, they show remarkable antibacterial activity against Escherichia coli (ATCC 25922). Thus, green synthesized RGO-supported palladium nanoparticles demonstrated that enhanced catalytic activity and antibacterial activity both play an important role in the environmental and medical disciplines. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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13 pages, 4634 KiB

Open AccessArticle

Characterization and Antibacterial Response of Silver Nanoparticles Biosynthesized Using an Ethanolic Extract of Coccinia indica Leaves

by Suresh V. Chinni, Subash C. B. Gopinath, Periasamy Anbu, Neeraj Kumar Fuloria, Shivkanya Fuloria, Praveena Mariappan, Kishonthani Krusnamurthy, Lebaka Veeranjaneya Reddy, Gobinath Ramachawolran, Subramaniam Sreeramanan and Sumitha Samuggam

Crystals 2021, 11(2), 97; https://doi.org/10.3390/cryst11020097 - 22 Jan 2021

Cited by 22 | Viewed by 3953

Abstract

The present study was planned to characterize and analyze the antimicrobial activity of silver nanoparticles (AgNP) biosynthesized using a Coccinia indica leaf (CIL) ethanolic extract. The present study included the preparation of CIL ethanolic extract using the maceration process, which was further used [...] Read more.

The present study was planned to characterize and analyze the antimicrobial activity of silver nanoparticles (AgNP) biosynthesized using a Coccinia indica leaf (CIL) ethanolic extract. The present study included the preparation of CIL ethanolic extract using the maceration process, which was further used for AgNP biosynthesis by silver nitrate reduction. Biosynthetic AgNPs were characterized using UV–Visible spectrometry, zeta potential analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectrometry. The biogenic AgNP and CIL extracts were further investigated against different bacterial strains for their antimicrobial activity. The surface plasmon resonance (SPR) signal at 425 nm confirmed AgNP formation. The SEM and TEM data revealed the spherical shape of biogenic AgNPs and size in the range of 8 to 48 nm. The EDX results verified the presence of Ag. The AgNPs displayed a zeta potential of −55.46 mV, suggesting mild AgNP stability. Compared to Gram-positive bacteria, the biogenic AgNPs demonstrated high antibacterial potential against Gram-negative bacteria. Based on the results, the current study concluded that AgNPs based on CIL extract have strong antibacterial potential, and it established that AgNP biosynthesis using CIL ethanol extract is an effective process. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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8 pages, 2517 KiB

Open AccessArticle

Effects of Al Composition and High-Temperature Atomic Layer-Deposited Al₂O₃ Layer on the Leakage Current Characteristics of AlGaN/GaN Schottky Barrier Diodes

by Jae-Hoon Lee, Jung-Hee Lee and Ki-Sik Im

Crystals 2021, 11(2), 87; https://doi.org/10.3390/cryst11020087 - 21 Jan 2021

Cited by 3 | Viewed by 2864

Abstract

AlGaN/GaN Schottky barrier diodes (SBDs) with high Al composition and high temperature atomic layer deposition (ALD) Al₂O₃ layers were investigated. Current–voltage (I–V), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and capacitance–voltage (C–V) measurements were conducted in order to find [...] Read more.

AlGaN/GaN Schottky barrier diodes (SBDs) with high Al composition and high temperature atomic layer deposition (ALD) Al₂O₃ layers were investigated. Current–voltage (I–V), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and capacitance–voltage (C–V) measurements were conducted in order to find the leakage current mechanism and reduce the reverse leakage current. The fabricated AlGaN/GaN SBDs with high Al composition exhibited two orders’ higher leakage current compared to the device with low Al composition (20%) due to large bulk and surface leakage components. The leakage current measured at −60 V for the fabricated SBD with Al₂O₃ deposited at temperature of 550 °C was decreased to 1.5 μA, compared to the corresponding value of 3.2 mA for SBD with nonpassivation layer. The high quality ALD Al₂O₃ deposited at high temperature with low interface trap density reduces the donorlike surface states, which effectively decreases surface leakage current of the AlGaN/GaN SBD. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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7 pages, 2008 KiB

Open AccessArticle

Influence of Thermal Annealing on the PdAl/Au Metal Stack Ohmic Contacts to p-AlGaN

by Siva Pratap Reddy Mallem, Woo-Hyun Ahn, Jung-Hee Lee and Ki-Sik Im

Crystals 2020, 10(12), 1091; https://doi.org/10.3390/cryst10121091 - 28 Nov 2020

Cited by 3 | Viewed by 3361

Abstract

In this study, a PdAl (20 nm)/Au (30 nm) metal stack scheme is used for forming low-ohmic-resistance contact on Mg-doped (1.5 × 10¹⁷ cm⁻³) p-type AlGaN at various annealing temperatures. Using a circular-transmission line model, the specific contact resistance ( [...] Read more.

In this study, a PdAl (20 nm)/Au (30 nm) metal stack scheme is used for forming low-ohmic-resistance contact on Mg-doped (1.5 × 10¹⁷ cm⁻³) p-type AlGaN at various annealing temperatures. Using a circular-transmission line model, the specific contact resistance (^ρ_c) of PdAl/Au/p-AlGaN ohmic contact is determined via the current–voltage (I–V) characteristics. As-deposited contacts demonstrate non-linear behavior. However, the contact exhibits linear I–V characteristics with excellent ohmic contact of _ρc = 1.74 × 10⁻⁴^Ωcm², when annealed at 600 °C for 1 min in a N₂ atmosphere. The Ga and Al vacancies created at the PdAl/Au and p-AlGaN interfaces, which act as acceptors to increase the hole concentration at the interface. The out-diffusion of Ga as well as in-diffusion of Pd and Au to form interfacial chemical reactions at the interface is observed by X-ray photoelectron spectroscopy (XPS) measurements. The phases of the Ga–Pd and Ga–Au phases are detected by X-ray diffraction (XRD) analysis. Morphological results show that the surface of the contact is reasonably smooth with the root-mean-square roughness of 2.89 nm despite annealing at 600 °C. Based on the above experimental considerations, PdAl/Au/p-AlGaN contact annealed at 600 °C is a suitable p-ohmic contact for the development of high-performance electronic devices. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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19 pages, 4678 KiB

Open AccessArticle

Multifunctional Hierarchically Architectured ZnO for Luminescence, Photocatalytic, Electrocatalytic, and Energy Storage Applications

by V. P. Singh, Mirgender Kumar, B. Purusottam Reddy, Sunny, R. K. Gangwar and Chandana Rath

Crystals 2020, 10(11), 1025; https://doi.org/10.3390/cryst10111025 - 10 Nov 2020

Cited by 5 | Viewed by 2310

Abstract

Hierarchically ZnO nanoarchitecture synthesized through coprecipitation technique. Growth process has been analyzed by varying pH from 5.5 to 13 along with post heat treatment process through the observation of surface morphology from 2D plates, triangular, hexagonal rods, needles, and finally to hierarchical. X-ray [...] Read more.

Hierarchically ZnO nanoarchitecture synthesized through coprecipitation technique. Growth process has been analyzed by varying pH from 5.5 to 13 along with post heat treatment process through the observation of surface morphology from 2D plates, triangular, hexagonal rods, needles, and finally to hierarchical. X-ray diffraction (XRD) reveals many intermediate phases along with ZnO which has been eliminated through the proper pH and temperature. The native defects have been discussed by using Raman and positron annihilation spectroscopy. Further, multifunctional properties of synthesized material have been discussed by candle-like warm white luminescence, photocatalysis, electrocatalysis and energy storage applications. Specially hierarchically nanoarchitecture found suitable for warm white lighting along with effective for waste water treatment by visible light. The highly porous property of the same material made itself appropriate for effective oxygen evaluation reaction and hydrogen evolution reaction together with reduced overpotential and Tafel slope. The application for supercapacitor electrode (~780 F/g) also has been revealed which opened new dimension for hierarchical ZnO. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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11 pages, 2944 KiB

Open AccessArticle

Facile Synthesis, Characterization, Anti-Microbial and Anti-Oxidant Properties of Alkylamine Functionalized Dumb-Bell Shaped Copper-Silver Nanostructures

by Koduru Mallikarjuna, Amal M. Al-Mohaimeed, Dunia A. Al-Farraj, Lebaka Veeranjaneya Reddy, Minnam Reddy Vasudeva Reddy and Arifullah Mohammed

Crystals 2020, 10(11), 966; https://doi.org/10.3390/cryst10110966 - 26 Oct 2020

Cited by 5 | Viewed by 2814

Abstract

Admirable studies have been established on the utilization of ligand-materials as bimetallic nanoparticles in the field of nanoscience and biotechnology. UV-Vis, XRD, HR-TEM, STEM-HAADF, EDS, FTIR, and DPPH analyses characterized the optical, structural, compositional morphological, and antioxidant properties of synthesized Cu-Ag nanostructures. The [...] Read more.

Admirable studies have been established on the utilization of ligand-materials as bimetallic nanoparticles in the field of nanoscience and biotechnology. UV-Vis, XRD, HR-TEM, STEM-HAADF, EDS, FTIR, and DPPH analyses characterized the optical, structural, compositional morphological, and antioxidant properties of synthesized Cu-Ag nanostructures. The spectrum of UV-Vis exhibited absorption bands at 590 and 413 nm, which reflects the surface plasmon resonance of copper-silver nanostructures. Herein, our exploration of alkylamine stabilized copper/silver nanostructures while using hexadecylamine as capping material and their primary biomedical investigation on antimicrobial and antioxidant studies is reported. Cu-Ag bimetallic nanostructures were more effective against gram-negative bacteria E. coli and Klebsiella when compared to gram-positive bacteria. The antioxidant activity of Cu-Ag nanoparticles was comparable with Ascorbic acid. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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7 pages, 1502 KiB

Open AccessArticle

Effects of GaN Buffer Resistance on the Device Performances of AlGaN/GaN HEMTs

by Ki-Sik Im, Jae-Hoon Lee, Yeo Jin Choi and Sung Jin An

Crystals 2020, 10(9), 848; https://doi.org/10.3390/cryst10090848 - 22 Sep 2020

Cited by 7 | Viewed by 3869

Abstract

We investigated the effects of GaN buffer resistance of AlGaN/GaN high-electron-mobility transistors (HEMTs) on direct current (DC), low-frequency noise (LFN), and pulsed I-V characterization performances. The devices with the highest GaN buffer resistance were grown on sapphire substrate using two-step growth [...] Read more.

We investigated the effects of GaN buffer resistance of AlGaN/GaN high-electron-mobility transistors (HEMTs) on direct current (DC), low-frequency noise (LFN), and pulsed I-V characterization performances. The devices with the highest GaN buffer resistance were grown on sapphire substrate using two-step growth temperature method without additional compensation doping. The proposed device exhibited the degraded off-state leakage current due to the improved GaN buffer quality compared to the reference devices with relative low buffer resistance, which is confirmed by high resolution X-ray diffraction (HRXRD). However, the proposed device with deep-level defects in GaN buffer layer showed the reduced hysteresis (∆V_th), increased breakdown voltage (BV), and enhanced pulse I-V characteristics. Regardless of GaN buffer resistance, all devices clearly showed 1/f behavior with carrier number fluctuations (CNF) at on-state but followed 1/f² characteristic at off-state. From the 1/f² noise characteristics, the extracted trap time constant (τ_i) of the proposed device can be obtained to be 10 ms, which is shorter than those of the reference devices because of the full compensation of deep-level defects in the GaN buffer layer. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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13 pages, 6369 KiB

Open AccessArticle

Development of Catalytic-CVD SiN_x Passivation Process for AlGaN/GaN-on-Si HEMTs

by Myoung-Jin Kang, Hyun-Seop Kim, Ho-Young Cha and Kwang-Seok Seo

Crystals 2020, 10(9), 842; https://doi.org/10.3390/cryst10090842 - 21 Sep 2020

Cited by 10 | Viewed by 4626

Abstract

We optimized a silicon nitride (SiN_x) passivation process using a catalytic-chemical vapor deposition (Cat-CVD) system to suppress the current collapse phenomenon of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). The optimized Cat-CVD SiN_x film exhibited a high film density of 2.7 [...] Read more.

We optimized a silicon nitride (SiN_x) passivation process using a catalytic-chemical vapor deposition (Cat-CVD) system to suppress the current collapse phenomenon of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). The optimized Cat-CVD SiN_x film exhibited a high film density of 2.7 g/cm³ with a low wet etch rate (buffered oxide etchant (BOE) 10:1) of 2 nm/min and a breakdown field of 8.2 MV/cm. The AlGaN/GaN-on-Si HEMT fabricated by the optimized Cat-CVD SiN_x passivation process, which had a gate length of 1.5 μm and a source-to-drain distance of 6 μm, exhibited the maximum drain current density of 670 mA/mm and the maximum transconductance of 162 mS/mm with negligible hysteresis. We found that the optimized SiN_x film had positive charges, which were responsible for suppressing the current collapse phenomenon. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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7 pages, 1466 KiB

Open AccessArticle

Low-Frequency Noise Behavior of AlGaN/GaN HEMTs with Different Al Compositions

by Yeo Jin Choi, Jae-Hoon Lee, Sung Jin An and Ki-Sik Im

Crystals 2020, 10(9), 830; https://doi.org/10.3390/cryst10090830 - 17 Sep 2020

Cited by 9 | Viewed by 3099

Abstract

Al_xGa_1−xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray [...] Read more.

Al_xGa_1−xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray diffraction (HRXRD). Al_xGa_1−xN/GaN high-electron mobility transistors (HEMTs) with different Al compositions were fabricated, characterized, and compared using the Hall effect, direct current (DC), and low-frequency noise (LFN). The device with high Al composition (28%) showed improved sheet resistance (R_sh) due to enhanced carrier confinement and reduced gate leakage currents caused by increased Schottky barrier height (SBH). On the other hand, the reduced noise level and the low trap density (N_t) for the device of 13% of Al composition were obtained, which is attributed to the mitigated carrier density and decreased dislocation density in the Al_xGa_1−xN barrier layer according to the declined Al composition. In spite of the Al composition, the fabricated devices exhibited 1/ƒ noise behavior with the carrier number fluctuation (CNF) model, which is proved by the curves of both (S_Id/I_d²) versus (g_m/I_d)² and (S_Id/I_d²) versus (V_gs–V_th). Although low Al composition is favorable to the reduced noise, it causes some problems like low R_sh and high gate leakage current. Therefore, the optimized Al composition in AlGaN/GaN HEMT is required to improve both noise and DC properties. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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7 pages, 2030 KiB

Open AccessArticle

Investigation of 1/f and Lorentzian Noise in TMAH-treated Normally-Off GaN MISFETs

by Ki-Sik Im, Mallem Siva Pratap Reddy, Yeo Jin Choi, Youngmin Hwang, Sung Jin An and Jea-Seung Roh

Crystals 2020, 10(8), 717; https://doi.org/10.3390/cryst10080717 - 18 Aug 2020

Cited by 3 | Viewed by 2781

Abstract

A tetramethyl ammonium hydroxide (TMAH)-treated normally-off Gallum nitride (GaN) metal-insulator-semiconductor field-effect transistor (MISFET) was fabricated and characterized using low-frequency noise (LFN) measurements in order to find the conduction mechanism and analyze the trapping behavior into the gate insulator as well as the GaN [...] Read more.

A tetramethyl ammonium hydroxide (TMAH)-treated normally-off Gallum nitride (GaN) metal-insulator-semiconductor field-effect transistor (MISFET) was fabricated and characterized using low-frequency noise (LFN) measurements in order to find the conduction mechanism and analyze the trapping behavior into the gate insulator as well as the GaN buffer layer. At the on-state, the noise spectra in the fabricated GaN device were 1/f^γ properties with γ ≈ 1, which is explained by correlated mobility fluctuations (CMF). On the other hand, the device exhibited Lorentzian or generation-recombination (g-r) noises at the off-state due to deep-level trapping/de-trapping into the GaN buffer layer. The trap time constants (τ_i) calculated from the g-r noises became longer when the drain voltage increased up to 5 V, which was attributed to deep-level traps rather than shallow traps. The severe drain lag was also investigated from pulsed I-V measurement, which is supported by the noise behavior observed at the off-state. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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13 pages, 3234 KiB

Open AccessArticle

Electrochemical Performance of 2D-Hierarchical Sheet-Like ZnCo₂O₄ Microstructures for Supercapacitor Applications

by Kumcham Prasad, Gutturu Rajasekhara Reddy, Megala Rajesh, P. Reddi Babu, Gnanendra Shanmugam, N. John Sushma, M. Siva Pratap Reddy, Borelli Deva Prasad Raju and Koduru Mallikarjuna

Crystals 2020, 10(7), 566; https://doi.org/10.3390/cryst10070566 - 1 Jul 2020

Cited by 33 | Viewed by 3947

Abstract

With the rapid improvement of the global economy, the role of energy has become even more vital in the 21st century. In this regard, energy storage/conversion devices have become a major, worldwide research focus. In response to this, we have prepared two-dimensional (2D)-hierarchical [...] Read more.

With the rapid improvement of the global economy, the role of energy has become even more vital in the 21st century. In this regard, energy storage/conversion devices have become a major, worldwide research focus. In response to this, we have prepared two-dimensional (2D)-hierarchical sheet-like ZnCo₂O₄ microstructures for supercapacitor applications using a simple hydrothermal method. The 2D-hierarchical sheet-like morphologies with large surface area and smaller thickness enhanced the contact area of active material with the electrolyte, which increased the utilization rate. We investigated the electrochemical performance of sheet-like ZnCo₂O₄ microstructures while using Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD), and Electrochemical impedance spectroscopy (EIS) analysis. The electrochemical results demonstrated that the ZnCo₂O₄ electrode possesses 16.13 mF cm⁻² of areal capacitance at 10 µA cm⁻² of current density and outstanding cycling performance (170% of capacitance is retained after 1000 cycles at 500 µA cm⁻²). The high areal capacitance and outstanding cycling performance due to the unique sheet-like morphology of the ZnCo₂O₄ electrode makes it an excellent candidate for supercapacitor applications. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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