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

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (31 August 2021) | Viewed by 53158

Special Issue Editor

School of Electronics Engineering, Kyungpook National University, Daegu, Korea
Interests: bio-inspired electronic materials and devices; GaN-related devices; ZnO/ZnS-based nanoparticles; optoelectronic/power devices

Special Issue Information

Dear Colleagues,

Recently, nano/micro and bio-inspired materials in wide-bandgap-semiconductor-based methodologies for developing optoelectronic and power devices have been increasing rapidly in the field of solid-state technology. Studies of the electrical, optical, structural, and morphological properties of wide-bandgap semiconductors have received enormous interest for future-generation devices. Further, significant advances have occurred in the growth of wide-bandgap semiconductors on different types of substrates in the crystalline field. Furthermore, considerable interest has arisen in the development of the photocatalytic properties of wide-bandgap semiconductors. There are several studies on biomaterials on wide-bandgap semiconductors. However, no biomaterials have demonstrated the required low cost and stability, owing to a lack of the desired inherent material characteristics. Therefore, it is important to establish strategies to find and fulfill these requirements including hybrid solid-state technologies. These are currently open questions, as well as hot and timely topics. The main contribution of the present Special Issue is “Nano/Micro and Bio-Inspired Materials on Wide-Bandgap Semiconductor-Based Optoelectronic/Power Devices”. We believe that this Issue is theoretically and practically needed at present to discover the outstanding future devices.

Dr. M. Siva Pratap Reddy
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • nanomaterial-based wide-bandgap crystal growth
  • bio-inspired materials on wide-bandgap-based devices
  • nanomaterials on wide-bandgap-based devices
  • micro-materials on wide-bandgap-based devices
  • nano/micro sized graphene/graphite on wide-bandgap-based devices
  • electrical properties
  • optical properties
  • mechanical properties
  • structural properties
  • morphological properties
  • photocatalytic properties
  • carrier transport properties
  • noise properties
  • low- and high-temperature studies
  • wide-bandgap-semiconductor-based optoelectronic devices
  • wide-bandgap-semiconductor-based power devices

Published Papers (21 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Editorial

Jump to: Research

3 pages, 168 KiB  
Editorial
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst12010067 - 04 Jan 2022
Viewed by 858
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

Research

Jump to: Editorial

16 pages, 3567 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11111292 - 25 Oct 2021
Cited by 13 | Viewed by 2314
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
Show Figures

Figure 1

13 pages, 8804 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11091097 - 09 Sep 2021
Cited by 17 | Viewed by 1889
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
Show Figures

Figure 1

9 pages, 2780 KiB  
Communication
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11091037 - 28 Aug 2021
Cited by 5 | Viewed by 1730
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
Show Figures

Figure 1

10 pages, 2929 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11080955 - 16 Aug 2021
Cited by 4 | Viewed by 1780
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
Show Figures

Figure 1

16 pages, 4068 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11060716 - 21 Jun 2021
Cited by 7 | Viewed by 1889
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
Show Figures

Figure 1

7 pages, 2600 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11050489 - 27 Apr 2021
Cited by 5 | Viewed by 1863
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 (Dit), 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 (Nit) 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
Show Figures

Figure 1

9 pages, 19010 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11050469 - 22 Apr 2021
Cited by 21 | Viewed by 2876
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
Show Figures

Figure 1

11 pages, 4734 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11040405 - 10 Apr 2021
Cited by 6 | Viewed by 2746
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
Show Figures

Figure 1

6 pages, 1738 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11030234 - 26 Feb 2021
Cited by 12 | Viewed by 3464
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
Show Figures

Graphical abstract

11 pages, 3178 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11020134 - 28 Jan 2021
Cited by 16 | Viewed by 2531
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
Show Figures

Figure 1

13 pages, 4634 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11020097 - 22 Jan 2021
Cited by 17 | Viewed by 3180
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
Show Figures

Figure 1

8 pages, 2517 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst11020087 - 21 Jan 2021
Cited by 3 | Viewed by 2313
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
Show Figures

Graphical abstract

7 pages, 2008 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10121091 - 28 Nov 2020
Cited by 3 | Viewed by 2767
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 (ρc) 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 × 10−4Ωcm2, 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
Show Figures

Figure 1

19 pages, 4678 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10111025 - 10 Nov 2020
Cited by 5 | Viewed by 1884
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
Show Figures

Graphical abstract

11 pages, 2944 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10110966 - 26 Oct 2020
Cited by 2 | Viewed by 2413
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
Show Figures

Graphical abstract

7 pages, 1502 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10090848 - 22 Sep 2020
Cited by 4 | Viewed by 3214
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 (∆Vth), 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 (τi) 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
Show Figures

Graphical abstract

13 pages, 6369 KiB  
Article
Development of Catalytic-CVD SiNx 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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10090842 - 21 Sep 2020
Cited by 9 | Viewed by 3872
Abstract
We optimized a silicon nitride (SiNx) 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 SiNx film exhibited a high film density of 2.7 [...] Read more.
We optimized a silicon nitride (SiNx) 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 SiNx 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 SiNx 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 SiNx film had positive charges, which were responsible for suppressing the current collapse phenomenon. Full article
Show Figures

Figure 1

7 pages, 1466 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10090830 - 17 Sep 2020
Cited by 7 | Viewed by 2502
Abstract
AlxGa1−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.
AlxGa1−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). AlxGa1−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 (Rsh) 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 (Nt) for the device of 13% of Al composition were obtained, which is attributed to the mitigated carrier density and decreased dislocation density in the AlxGa1−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 (SId/Id2) versus (gm/Id)2 and (SId/Id2) versus (Vgs–Vth). Although low Al composition is favorable to the reduced noise, it causes some problems like low Rsh 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
Show Figures

Graphical abstract

7 pages, 2030 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10080717 - 18 Aug 2020
Cited by 3 | Viewed by 2316
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/fγ 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 (τi) 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
Show Figures

Graphical abstract

13 pages, 3234 KiB  
Article
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://0-doi-org.brum.beds.ac.uk/10.3390/cryst10070566 - 01 Jul 2020
Cited by 31 | Viewed by 3251
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
Show Figures

Figure 1

Back to TopTop