III-nitride semiconductors are promising optoelectronic and electronic materials and have been extensively investigated in the past decades. New functionalities, such as ferroelectricity, ferromagnetism, and superconductivity, have been implanted into III-nitrides to expand their capability in next-generation semiconductor and quantum technologies. The recent experimental demonstration of ferroelectricity in nitride materials, including ScAl(Ga)N, boron-substituted AlN, and hexagonal BN, has inspired tremendous research interest. Due to the large remnant polarization, high breakdown field, high Curie temperature, and significantly enhanced piezoelectric, linear and nonlinear optical properties, nitride ferroelectric semiconductors have enabled a wealth of applications in electronic, ferroelectronic, acoustoelectronic, optoelectronic, and quantum devices and systems. In this review, the development of nitride ferroelectric semiconductors from materials to devices is discussed. While expounding on the unique advantages and outstanding achievements of nitride ferroelectrics, the existing challenges and promising prospects have been also discussed.
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Ping Wang et al 2023 Semicond. Sci. Technol. 38 043002
Austin Lee Hickman et al 2021 Semicond. Sci. Technol. 36 044001
Gallium nitride high-electron-mobility transistors (GaN HEMTs) are at a point of rapid growth in defense (radar, SATCOM) and commercial (5G and beyond) industries. This growth also comes at a point at which the standard GaN heterostructures remain unoptimized for maximum performance. For this reason, we propose the shift to the aluminum nitride (AlN) platform. AlN allows for smarter, highly-scaled heterostructure design that will improve the output power and thermal management of III-nitride amplifiers. Beyond improvements over the incumbent amplifier technology, AlN will allow for a level of integration previously unachievable with GaN electronics. State-of-the-art high-current p-channel FETs, mature filter technology, and advanced waveguides, all monolithically integrated with an AlN/GaN/AlN HEMT, is made possible with AlN. It is on this new AlN platform that nitride electronics may maximize their full high-power, high-speed potential for mm-wave communication and high-power logic applications.
Yoshihiko Muramoto et al 2014 Semicond. Sci. Technol. 29 084004
Ultraviolet light-emitting diodes (UV-LEDs) have started replacing UV lamps. The power per LED of high-power LED products has reached 12 W (14 A), which is 100 times the values observed ten years ago. In addition, the cost of these high-power LEDs has been decreasing. In this study, we attempt to understand the technologies and potential of UV-LEDs.
Meint Smit et al 2014 Semicond. Sci. Technol. 29 083001
Photonic integrated circuits (PICs) are considered as the way to make photonic systems or subsystems cheap and ubiquitous. PICs still are several orders of magnitude more expensive than their microelectronic counterparts, which has restricted their application to a few niche markets. Recently, a novel approach in photonic integration is emerging which will reduce the R&D and prototyping costs and the throughput time of PICs by more than an order of magnitude. It will bring the application of PICs that integrate complex and advanced photonic functionality on a single chip within reach for a large number of small and larger companies and initiate a breakthrough in the application of Photonic ICs. The paper explains the concept of generic photonic integration technology using the technology developed by the COBRA research institute of TU Eindhoven as an example, and it describes the current status and prospects of generic InP-based integration technology.
Daniele Ielmini 2016 Semicond. Sci. Technol. 31 063002
With the explosive growth of digital data in the era of the Internet of Things (IoT), fast and scalable memory technologies are being researched for data storage and data-driven computation. Among the emerging memories, resistive switching memory (RRAM) raises strong interest due to its high speed, high density as a result of its simple two-terminal structure, and low cost of fabrication. The scaling projection of RRAM, however, requires a detailed understanding of switching mechanisms and there are potential reliability concerns regarding small device sizes. This work provides an overview of the current understanding of bipolar-switching RRAM operation, reliability and scaling. After reviewing the phenomenological and microscopic descriptions of the switching processes, the stability of the low- and high-resistance states will be discussed in terms of conductance fluctuations and evolution in 1D filaments containing only a few atoms. The scaling potential of RRAM will finally be addressed by reviewing the recent breakthroughs in multilevel operation and 3D architecture, making RRAM a strong competitor among future high-density memory solutions.
Hannah J Joyce et al 2016 Semicond. Sci. Technol. 31 103003
Accurately measuring and controlling the electrical properties of semiconductor nanowires is of paramount importance in the development of novel nanowire-based devices. In light of this, terahertz (THz) conductivity spectroscopy has emerged as an ideal non-contact technique for probing nanowire electrical conductivity and is showing tremendous value in the targeted development of nanowire devices. THz spectroscopic measurements of nanowires enable charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities to be measured with high accuracy and high throughput in a contact-free fashion. This review spans seminal and recent studies of the electronic properties of nanowires using THz spectroscopy. A didactic description of THz time-domain spectroscopy, optical pump–THz probe spectroscopy, and their application to nanowires is included. We review a variety of technologically important nanowire materials, including GaAs, InAs, InP, GaN and InN nanowires, Si and Ge nanowires, ZnO nanowires, nanowire heterostructures, doped nanowires and modulation-doped nanowires. Finally, we discuss how THz measurements are guiding the development of nanowire-based devices, with the example of single-nanowire photoconductive THz receivers.
James Semple et al 2017 Semicond. Sci. Technol. 32 123002
Over the last decade, there has been increasing interest in transferring the research advances in radiofrequency (RF) rectifiers, the quintessential element of the chip in the RF identification (RFID) tags, obtained on rigid substrates onto plastic (flexible) substrates. The growing demand for flexible RFID tags, wireless communications applications and wireless energy harvesting systems that can be produced at a low-cost is a key driver for this technology push. In this topical review, we summarise recent progress and status of flexible RF diodes and rectifying circuits, with specific focus on materials and device processing aspects. To this end, different families of materials (e.g. flexible silicon, metal oxides, organic and carbon nanomaterials), manufacturing processes (e.g. vacuum and solution processing) and device architectures (diodes and transistors) are compared. Although emphasis is placed on performance, functionality, mechanical flexibility and operating stability, the various bottlenecks associated with each technology are also addressed. Finally, we present our outlook on the commercialisation potential and on the positioning of each material class in the RF electronics landscape based on the findings summarised herein. It is beyond doubt that the field of flexible high and ultra-high frequency rectifiers and electronics as a whole will continue to be an active area of research over the coming years.
Yuting Li et al 2024 Semicond. Sci. Technol. 39 065004
This paper demonstrates low-resistance and high-transparency p-type contact materials for ultraviolet (UV) micro-light-emitting diodes (LEDs) at 365 nm. As a commonly used p-type LED contact, indium tin oxide (ITO) and nickel/ITO (Ni/ITO) contacts were studied before and after rapid thermal annealing (RTA) treatments. The transmittance at 365 nm wavelength of 200 nm thick ITO films increased from approximately 57%–90% after RTA at a temperature exceeding 400 °C, while the Ni/ITO film had a transmittance of about 73% after annealing. Micron-sized UV-LEDs with Ni/ITO p-contact were fabricated. Electrical characterization shows that Ni/ITO films annealed at 600 °C demonstrated good ohmic contact behavior and the highest on-wafer external quantum efficiency, despite slightly lower transmittance. This paper shows the potential of annealed Ni/ITO films as promising p-contact materials for high-performance 365 nm UV-LEDs.
Daisuke Iida and Kazuhiro Ohkawa 2022 Semicond. Sci. Technol. 37 013001
GaN-based light-emitting devices have the potential to realize all visible emissions with the same material system. These emitters are expected to be next-generation red, green, and blue displays and illumination tools. These emitting devices have been realized with highly efficient blue and green light-emitting diodes (LEDs) and laser diodes. Extending them to longer wavelength emissions remains challenging from an efficiency perspective. In the emerging research field of micro-LED displays, III-nitride red LEDs are in high demand to establish highly efficient devices like conventional blue and green systems. In this review, we describe fundamental issues in the development of red LEDs by III-nitrides. We also focus on the key role of growth techniques such as higher temperature growth, strain engineering, nanostructures, and Eu doping. The recent progress and prospect of developing III-nitride-based red light-emitting devices will be presented.
Yuhao Zhang et al 2021 Semicond. Sci. Technol. 36 054001
Gallium nitride (GaN) is becoming a mainstream semiconductor for power and radio-frequency (RF) applications. While commercial GaN devices are increasingly being adopted in data centers, electric vehicles, consumer electronics, telecom and defense applications, their performance is still far from the intrinsic GaN limit. In the last few years, the fin field-effect transistor (FinFET) and trigate architectures have been leveraged to develop a new generation of GaN power and RF devices, which have continuously advanced the state-of-the-art in the area of microwave and power electronics. Very different from Si digital FinFET devices, GaN FinFETs have allowed for numerous structural innovations based on engineering the two-dimensional-electron gas or p–n junctions, in both lateral and vertical architectures. The superior gate controllability in these fin-based GaN devices has not only allowed higher current on/off ratio, steeper threshold swing, and suppression of short-channel effects, but also enhancement-mode operation, on-resistance reduction, current collapse alleviation, linearity improvement, higher operating frequency, and enhanced thermal management. Several GaN FinFET and trigate device technologies are close to commercialization. This review paper presents a global overview of the reported GaN FinFET and trigate device technologies for RF and power applications, as well as provides in-depth analyses correlating device design parameters to device performance space. The paper concludes with a summary of current challenges and exciting research opportunities in this very dynamic research field.
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Zengfa Chen et al 2024 Semicond. Sci. Technol. 39 075002
A normally-off vertical gallium nitride (GaN) junction field-effect transistor (JFET) is demonstrated in this work. The device shows an on/off current ratio of 3.6 × 1010, a threshold voltage (VTH) of 1.64 V, and a specific on-resistance (RON,SP) of 1.87 mΩ·cm2. Drain-induced channel effects were proposed to explain the change in the gate current at different drain voltages. Drain current decline in the output characteristics and the reverse turn-on between drain and source can be explained by effects. A technological computer-aided design was used to simulate the change of the depletion region and confirm the explanation. Detailed analyses of the channel effects provide a reference for the design of novel structures. The characteristics at different temperatures demonstrated the stability of threshold voltage and specific on-resistance, thus indicating the great potential of applications in switching power circuits of vertical GaN JFETs.
Yehong Li et al 2024 Semicond. Sci. Technol. 39 075001
In this paper, a beta-phase gallium oxide (β-Ga2O3) vertical FinFET with diamond-gate has been studied by Silvaco-ATLAS simulation. The diamond-gate structure achieves adjustable pin (p-insulator-n) junction owing to the diamond-SiO2-Ga2O3 heterostructure. This design also enhances heat dissipation by virtue of the high thermal conductivity of the diamond. Compared to conventional FinFETs, the diamond-gate FinFET (DG-FinFET) reduces the static operating temperature rise by around 17.30%. Additionally, due to its greater heat dissipation capacity, DG-FinFETs provide a 5.84% increase in current density at 1 kA cm−2 current density level. The structural changes in the diamond-gate also result in a significant reduction in the gate-source capacitance (CGS). At 1 MHz operating frequency and the same gate voltage, DG-FinFETs have 69.29% less gate-source charge (QGS), 70.80% less charge/discharge delay time, 73.70% less switching loss, and 57.15% less conduction loss. Overall, the simulation and analysis presented in this work indicate a promising advancement of the DG-FinFET structure in high-power and rapid switching applications.
Harshit Kansal and Aditya Sankar Medury 2024 Semicond. Sci. Technol. 39 065020
Dielectrically modulated (DM) negative capacitance field effect transistor (NCFET)-based label-free biosensors have emerged as promising devices for accurate detection of various biomolecules, where the sensitivity of DM architectures strongly depends on the sensing mechanism as well as on the size of the nanocavity. Therefore, to achieve higher sensitivity along with reduced fabrication complexity, we propose to utilize a pre-existing drain-side spacer region as a nanocavity, in a fully depleted silicon-on-insulator-based NCFET architecture. The ferroelectric (FE) layer in the metal-ferroelectric-insulator-semiconductor configuration meaningfully alters the impact of the drain's electric field on the source-side electrostatics, which results in higher sensitivity. Having quantified the sensitivity of an FE-dielectric (FE-DE) gate-stack-based NCFET biosensor, we now propose to include a paraelectric (PE) layer between the FE and DE materials, thus modifying the gate stack from FE-DE to FE-PE-DE with an equivalent negative capacitance seen from both stacks; here, a remarkable improvement is seen in the FE-PE-DE gate-stack-based NCFET, with nearly identical linearity performance, as seen from the high Pearson's coefficient value ( 0.9). Therefore, to illustrate the efficacy of the proposed sensing mechanism and the modified gate stack (FE-PE-DE), DE constant () values in the range of = 4.5 to = 75.99 are considered. Finally, the effect of scaling the channel length () on the sensitivity of the FE-PE-DE NCFET device is shown, and a high value, particularly at lower permittivity, demonstrates the versatility and wide applicability of the proposed NCFET biosensor.
Shalu Gupta and Rakesh Kumar 2024 Semicond. Sci. Technol. 39 065019
This study demonstrates a proficient and eco-friendly synthesis of SnO2 nanostructures using a hydrothermal method, without the requirement of extra surfactants. The synthesis was systematically performed by adjusting the molar ratio of stannic chloride to sodium hydroxide and varying the pH settings. It was noted that the pH value rises according to the concentration of sodium hydroxide. A comprehensive analysis was performed to characterize the resulting nanostructures, which involved studying their structural features, chemical composition, morphology, and optical properties. An x-ray diffraction analysis showed that increasing the pH values resulted in a noticeable improvement in the crystalline structure and a decrease in the density of surface defects. The SnO2 nanostructures, synthesized using different pH settings, were subsequently assessed for their photocatalytic performance in the degradation of methylene blue dye under simulated solar irradiation. Surprisingly, the nanostructure produced at higher pH levels showed outstanding results, as 97% of the dye was broken down in just 70 min when exposed to simulated solar radiation. The analysis uncovered a maximum rate constant (k) value of 0.04 min−1, determined using pseudo first-order rate kinetics. In order to better understand the photodegradation process, scavenger experiments were performed to identify the active species involved. These investigations provided valuable insights into the complex mechanisms that drive the observed photocatalytic activity. This study not only enhances the progress of SnO2 nanostructures but also highlights their potential as strong and environmentally friendly materials for effective photocatalytic applications.
Thanh C Pham et al 2024 Semicond. Sci. Technol. 39 065017
Analytical models for investigating Metal–Semiconductor (M–S) ohmic contacts in test structures have conventionally included resistive-only contact interfaces. Given that M–S contacts are fundamentally governed by electron tunnelling across the potential energy barrier at the M–S interface, this simplified approach may result in misinterpretation. This paper describes, in detail, a novel Resistor-to-Schottky (RSB) barrier analytical model that enables a more in-depth exploration of the physics underlying ohmic contacts. The proposed model is analysed and compared with models constructed using the semiconductor device simulator tool TCAD. The study reveals significant differences in outcomes when employing the RSB model rather than the conventional Transmission Line model and contributes to a more comprehensive understanding of M–S ohmic contacts in test structures.
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Hao Chen et al 2024 Semicond. Sci. Technol. 39 063001
Due to the excellent responsivity and high rejection ratio, Ga2O3-based solar-blind ultraviolet photodetectors (PDs) are attracting more and more attention. The excellent material quality ensures great performance of PDs. In this review, we summarize recent advancements in growth methods of β-Ga2O3 bulk and thin films. Based on high-quality substrates and thin films, numerous state-of-art Ga2O3-based PDs have been reported in decades. Therefore, we collect some representative achievements in Ga2O3-based PDs, summarizing the development process of each type of structure. Furthermore, the advantages and disadvantages of different structures are also discussed to provide practical reference for researchers in this field. Additionally, inspired by the excellent performance of Ga2O3-based PDs, many research teams have also explored the applications based on solar-blind detection. We summarize three application fields, including imaging, light communication, and optical tracing, introducing some excellent works from different teams. Finally, we evaluate the outlook and remaining challenges in the future development of Ga2O3-based PDs.
Xinglin Liu et al 2024 Semicond. Sci. Technol. 39 043001
Wide bandgap semiconductor gallium oxide (β-Ga2O3) has emerged as a prominent material in the field of high-power microelectronics and optoelectronics, due to its excellent and stable performance. However, the lack of high-quality p-type β-Ga2O3 hinders the realization of its full potential. Here, we initially summarize the origins of p-type doping limitation in β-Ga2O3, followed by proposing four potential design strategies to enhance the p-type conductivity of β-Ga2O3. (i) Lowering the formation energy of acceptors to enhance its effective doping concentration. (ii) Reducing the ionization energy of acceptors to increase the concentration of free holes in the valence band maximum (VBM). (iii) Increasing the VBM of β-Ga2O3 to decrease the ionization energy of acceptors. (iv) Intrinsic defect engineering and nanotechnology of β-Ga2O3. For each strategy, we illustrate the design principles based on fundamental physical theories along with specific examples. From this review, one could learn the p-type doping strategies for β-Ga2O3.
Yuhai Yuan and Yanfeng Jiang 2024 Semicond. Sci. Technol. 39 033001
Magnetic tunnel junctions (MTJs), as the core storage unit of magneto resistive random-access memory, plays important role in the cutting-edge spintronics. In the MTJ devices, there are multiple internal magnetic/nonmagnetic heterojunction structures. The heterojunction always consists of magnetic metals and magnetic insulators or nonmagnetic metals. The interface of the heterojunction has certain physical effects that can affect the performance of MTJ devices. In the review, combined with the existing research results, the physical mechanism of magnetic/non-magnetic heterojunction interface coupling is discussed. The influence of the interface effect of the heterojunction on the performance of MTJ devices is studied. The optimization method is proposed specifically. This work systematically summarizes the interface effect of magnetic/non-magnetic heterojunction, which could be the critical aspect for the device's yield and reliability.
Mitsuru Funato et al 2024 Semicond. Sci. Technol. 39 013002
This paper reviews the development of three-dimensional (3D) structure-controlled InGaN quantum wells (QWs) for highly efficient multiwavelength emitters without using phosphors. Specifically, two representative structures are reviewed: 3D structures composed of stable planes with low surface energies and 3D structures composed of unstable planes. In the early stage of the research, 3D structures were grown on the (0001) polar plane through the selective area growth (SAG) technique based on metalorganic vapor phase epitaxy. Because GaN cannot grow on dielectric masks, different mask patterns were used to create various 3D facetted structures composed of stable facet planes. The InGaN QW parameters depend on the facet planes, which led to polychromatic emission, including white-light emission. After polychromatic light-emitting diodes (LEDs) on the (0001) polar plane were demonstrated, 3D QWs and LEDs were also demonstrated on the (2) semipolar plane through SAG. There, the (0001) facet plane was excluded; consequently, all the facet QWs showed short radiative recombination lifetimes, which are beneficial for future applications in visible-light communication. To further enhance the controllability of the emission spectra from 3D QWs or LEDs, convex-lens-shaped 3D structures have been proposed. The smooth surface of such structures is composed of unstable planes and has continuously varying crystal tilts. Because QW parameters are dependent on the crystal tilt, polychromatic emission is achieved. This method demonstrates greater flexibility of the structure design, which is expected to result in greater controllability of emission spectra.
Garima Rana et al 2024 Semicond. Sci. Technol. 39 013001
Photocatalytic H2 evolution and CO2 reduction are promising technologies for addressing environmental and energy issues. g-C3N4 is one of most promising materials to form improved catalysts because of its exceptional electrical structure, physical and chemical characteristics, and distinctive metal-free feature. This article provides a summary of current advancements in g-C3N4-based catalysts from innovative design approaches and their applications. Hydrogen evolution has reached 6305.18 µmol g−1 h−1 and >9 h of stability using the SnS2/g-C3N4 heterojunction. Additionally, the ZnO/Au/g-C3N4 maintains a constant CO generation rate of 689.7 mol m−2 during the 8 h reaction. To fully understand the interior relationship of theory–structure performance on g-C3N4-based materials, modifications are studied simultaneously. Furthermore, the synthesis of g-C3N4 and g-C3N4-based materials, as well as their respective instances, have been reported. The reduction of CO2 and H2 generation is summarized. Lastly, a short overview of the present issues and potential alternatives for g-C3N4-based materials is provided.
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Jhang et al
This study proposes a bipolar resistive random-access memory (RRAM), which is fabricated using an aluminum oxide (AlOx) resistive switching (RS) layer. The RRAM shows a large memory window of 106 at a low read voltage of 0.5 V. In addition, high switching speed, high data retention capability, and superior read-disturb immunity are observed. AlOx layers are prepared by a thermal oxidation growth process. Aluminum metal films deposited on n+-Si wafers are oxidized at O2/(O2+N2) flow rate ratios of 50-100%. Al/AlOx/n+-Si device shows no RS behavior when the AlOx is grown in a pure O2 environment. As the O2/(O2+N2) flow rate ratio decreases to 50%, Al/AlOx:N/n+-Si device reveals stable bipolar RS characteristics. A filamentary mode based on oxygen interstitial and Al vacancy is proposed to explain the difference in electrical characteristics of AlOx devices prepared at different O2 flow rates.
Zhou et al
In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in AlN single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
Li et al
Applying the valley contrasting properties of valleytronic materials to logical operations is the foundation of valleytronic device manufacturing. It is predicted that single-layer LaCl2 is an ferrovalley material with intrinsic and tunable valley polarization through first-principles calculations. It is a ferromagnetic semiconductor (bandgap 0.767 eV) with roughly 1.0 μB per unit cell as well as out of plane magnetization, and the Curie temperature is about 149 K. The tight-binding model considering five orbitals as well as next nearest neighboring hopping get a consistent band structure with the first-principles calculation. The valley polarization changes from 40.49 to 98.51 meV under the biaxial strain of 5% ~ -5%. Therefore, the biaxial strain can be a means to tune the valley polarization. In addition, the valley polarization of the double-layer structure (~ 80 meV) is much greater than that of the single-layer structure (~ 59 meV) due to the increased magnetic moment of the double-layer structure, indicating the potential tunable character by stacking few layers. We believe that single-layer LaCl2 has great potential for device manufacturing and application in the field of valley electronics.
Jose et al
The mean inner potential (MIP), V0, for a series of Zn group VI semiconductor nanostructures were measured experimentally using off-axis electron holography (EH). Values for ZnS, ZnTe and ZnO were remeasured and new values were added for ZnSe and ZnSSe nanowires. We confirm that the MIP increases non-linearly with
mass density beginning at 12.4 ± 0.2 V for the lowest density ZnS and slowly increasing with composition to
12.9 ± 0.2 V for ZnSe, more rapidly for ZnTe and with a significant increase to 14.8 ± 0.3 V for ZnO with the
highest density. Published results from DFT calculations compared well to these measurements with similar
trends apparent for other cation families such as the Ga-III-V.
Sun et al
Distributed Bragg reflectors have been widely utilized in GaN-based flip-chip light-emitting diodes (FCLEDs) owing to their excellent reflection performance. Recently, wide reflected angle DBR (WRA-DBR) has been suggested to enhance the optical characteristics of GaN-based FCLEDs by incorporating multiple sub-DBRs with varying central wavelengths. However, the reflectivity of WRA-DBR decreases at large incident angle from 425 nm to 550 nm, which restricts further optical performance improvement of FCLEDs. Here, we demonstrate a quintuple-stack DBR comprised of five sub-DBRs. The quintuple-stack DBR possesses a high reflectivity (>97.5%) for incident angles below 50° within the blue and green light wavelength ranges. Compared to WRA-DBR, quintuple-stack DBR exhibits a higher reflectivity in wavelength range of 425 nm to 550 nm and thinner multilayer thicknesses. Furthermore, stronger electric field intensities exist in the top facet and sidewalls of FCLED with quintuple-stack DBR, revealing that quintuple-stack DBR is beneficial for enhancing the light extraction efficiency. As a result, the light output power of FCLED with quintuple-stack DBR is ~3% higher than that of FCLED with WRA-DBR at 750 mA.
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Jingan Zhou et al 2024 Semicond. Sci. Technol.
In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in AlN single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
Thanh C Pham et al 2024 Semicond. Sci. Technol. 39 065017
Analytical models for investigating Metal–Semiconductor (M–S) ohmic contacts in test structures have conventionally included resistive-only contact interfaces. Given that M–S contacts are fundamentally governed by electron tunnelling across the potential energy barrier at the M–S interface, this simplified approach may result in misinterpretation. This paper describes, in detail, a novel Resistor-to-Schottky (RSB) barrier analytical model that enables a more in-depth exploration of the physics underlying ohmic contacts. The proposed model is analysed and compared with models constructed using the semiconductor device simulator tool TCAD. The study reveals significant differences in outcomes when employing the RSB model rather than the conventional Transmission Line model and contributes to a more comprehensive understanding of M–S ohmic contacts in test structures.
Anitha Jose et al 2024 Semicond. Sci. Technol.
The mean inner potential (MIP), V0, for a series of Zn group VI semiconductor nanostructures were measured experimentally using off-axis electron holography (EH). Values for ZnS, ZnTe and ZnO were remeasured and new values were added for ZnSe and ZnSSe nanowires. We confirm that the MIP increases non-linearly with
mass density beginning at 12.4 ± 0.2 V for the lowest density ZnS and slowly increasing with composition to
12.9 ± 0.2 V for ZnSe, more rapidly for ZnTe and with a significant increase to 14.8 ± 0.3 V for ZnO with the
highest density. Published results from DFT calculations compared well to these measurements with similar
trends apparent for other cation families such as the Ga-III-V.
Khush Gohel et al 2024 Semicond. Sci. Technol.
High power operation of high electron mobility transistors (HEMTs) is limited due to a variety of thermal resistances in the HEMT device causing self-heating effects (SHEs) in the device. To reduce the SHEs, diamond heat spreaders integrated to the device have proven efficient for heat extraction from the device. In this report using electro-thermal TCAD simulations, we demonstrate an understanding of multiway heat extraction utilizing diamond heat spreaders for improving HEMT thermal performance at high DC output power density
(~40 W/mm). The impact of each heat extraction pathway is understood while considering the thermal boundary resistance between Diamond/GaN hetero-interface and optimization of the GaN buffer layer thickness. Using these findings, we simulated an AlGaN/GaN HEMT device operating at 40 W/mm DC output power while maintaining device temperature at approximately 470 - 500 K.
Getye Behailu Yitagesu et al 2024 Semicond. Sci. Technol.
Today's energy demand is highly increased with the world's population growth and technological advancement. Natural dye-sensitized solar cells (N-DSSCs) are attracting research areas as an alternative and renewable energy source due to their simple preparation technique, availability, cost-effectiveness, and environmentally friendliness. In the present work, we have successfully fabricated DSSC from Thymus schimperi Ronniger plant flowers for the first time. The solvents used for extraction of the flower dye were deionized water and its mixture with ethanol. The Thymus schimperi Ronniger flowers extracted dye solutions and sensitized photoanodes were characterized by FTIR and UV-Vis characterization techniques. The crystallinity of TiO2 film was analyzed by the XRD technique and shows pure anatase phase behavior. The photoelectrochemical solar cell performance parameters, like, short circuit current density (JSC), open circuit voltage VOC), fill factor (FF), and efficiency were evaluated from the current density-voltage (J-V) measurement using a Keithley 2450 source meter. DSSC sensitized with extracted dye solution by the mixture of water and ethanol showed better performance (1.37%) as compared with that of extracted dye solution by Deionized water alone (1,02%). 

Keywords: Renewable energy, Dye-sensitized solar cells, Thymus Schimperi Ronniger, photoelectrochemical
Yuting Li et al 2024 Semicond. Sci. Technol. 39 065004
This paper demonstrates low-resistance and high-transparency p-type contact materials for ultraviolet (UV) micro-light-emitting diodes (LEDs) at 365 nm. As a commonly used p-type LED contact, indium tin oxide (ITO) and nickel/ITO (Ni/ITO) contacts were studied before and after rapid thermal annealing (RTA) treatments. The transmittance at 365 nm wavelength of 200 nm thick ITO films increased from approximately 57%–90% after RTA at a temperature exceeding 400 °C, while the Ni/ITO film had a transmittance of about 73% after annealing. Micron-sized UV-LEDs with Ni/ITO p-contact were fabricated. Electrical characterization shows that Ni/ITO films annealed at 600 °C demonstrated good ohmic contact behavior and the highest on-wafer external quantum efficiency, despite slightly lower transmittance. This paper shows the potential of annealed Ni/ITO films as promising p-contact materials for high-performance 365 nm UV-LEDs.
Lourdes Nicole Dela Rosa et al 2024 Semicond. Sci. Technol.
In this work, the terahertz (THz) time-domain spectroscopy was employed in studying the carrier dynamics in low-temperature grown (LT-) and semi-insulating (SI-) gallium arsenide (GaAs) photoconductive antenna (PCA) at above- (λ = 780 nm, Eg = 1.59 eV) and below- (λ = 1.55 μm, Eg 0.80 eV) bandgap excitation. We measured the excitation power dependence of the LT-GaAs (SI-GaAs) THz emission. Then,
the equivalent circuit model (ECM) which considers the (i) photogeneration, (ii) screening effects, and (iii) transport of carriers was utilized in analyzing the THz radiation mechanisms in the above- and below-bandgap excitation of the two substrates. In simulating the above-bandgap THz emission of both PCAs, we employed the direct bandgap excitation model which takes into account the
band-to-band transitions of photoexcited carriers. Meanwhile, to simulate the LT-GaAs (SI-GaAs) THz emission at below-bandgap excitation we utilized the two-step photoabsporption facilitated by the mid-gap states. In this model the
photoexcited carriers jump from the valence band to the mid-gap states and then to the conduction band. Results suggest that the THz emission from LT-GaAs and SI-GaAs at above- and below-bandgap excitation occur due to band-to-band
transitions, and two-step photoabsorption process via midgap states, respectively.
Yihang Qiu and Li Wei 2024 Semicond. Sci. Technol. 39 055004
A novel GaN trench gate vertical MOSFET (PSGT-MOSFET) with a double-shield structure composed of a separated gate (SG) and a p-type shielding layer (P_shield) is proposed and investigated. The P_shield is positioned within the drift region, which can suppress the electric field peak at the bottom of the trench during the off state. This helps to prevent premature breakdown of the gate oxide layer. Additionally, the presence of P_shield enables the device to have adaptive voltage withstand characteristics. The SG can convert a portion of gate-to-drain capacitance (Cgd) into drain-to-source capacitance (Cds), significantly reducing the gate-to-drain charge of the device. This improvement in charge distribution helps enhance the switching characteristics of the device. Later, the impact of the position and length of the P_shield on the breakdown voltage (BV) and specific on-resistance (Ron_sp) was studied. The influence of the position and length of the SG on gate charge (Qgd) and BV was also investigated. Through TCAD simulations, the parameters of P_shield and SG were optimized. Compared to conventional GaN TG-MOSFET with the same structural parameters, the gate charge was reduced by 88%. In addition, this paper also discusses the principle of adaptive voltage withstand in PSGT-MOSFET.
Carolina J Diliegros-Godines and Francisco Javier Flores-Ruiz 2024 Semicond. Sci. Technol. 39 045003
The overall performance of the multilayer resulting in a sol-gel bismuth ferrite (BiFeO3) film will be primarily determined by the properties of the first layer, but this has yet to receive much attention, even though chemical and morphological defects of this layer can accumulate as the number of layers increases. Here, we perform an optical, conductive, and ferroelectric study of first layer (L1) dip-coating sol-gel BiFeO3 films using two routes that vary only in the dissolvent; the first one is based on 2-methoxyethanol (MOE), and the second one on acetic acid (AA) with some MOE (AA-MOE). Tauc plots reveal a band gap of 2.43 eV and 2.75 eV for MOE (30 ± 5 nm thick) and AA-MOE (35 ± 5 nm thick) films, respectively. MOE films showed a dielectric function with features at ∼2.5 eV, ∼3.1 eV, and ∼3.9 eV, which were associated with charge-transfer transitions, but such features are absent in AA-MOE films. Advanced atomic force microscopy techniques were used to identify the fine features or defects of the BiFeO3 films: The conductive maps show that the charge transport pathways in both film routes are controlled by nanometer defects rather than grain or grain boundary defects. Current-voltage curves reveal high conductive pathway at a lower voltage for the MOE films than for AA-MOE films. The piezoelectric coefficient for MOE films was ∼20% higher than AA-MOE films. Both deposition methods yield ferroelectric films with an electromechanical strain controlled by the piezoelectric effect and minimal contribution from electrostriction. An optimization for the AA-MOE-based route in the withdrawal speed results in a significant reduction of morphological defects and a more than twofold increase in the piezoelectric coefficient. Our results broaden the understanding of optical and ferroelectric BiFeO3 films based on a chemical solution by dip-coating.
Lara Sophie Theurer et al 2024 Semicond. Sci. Technol. 39 035009
An experimental study of straight and bent distributed Bragg reflector (DBR) ridge waveguide (RW) lasers and Fabry–Pérot (FP) RW lasers emitting at 785 nm is presented. To determine the losses introduced by the bent waveguides within DBR-RW lasers, different laser designs were manufactured and characterized. The bent waveguides investigated here within DBR-RW laser diodes are sine-shaped S-bends. S-bends with three different lateral offsets are manufactured. The experimental characterization of FP lasers and the straight DBR-RW lasers with different coatings at the rear facet enables a rough estimation of the losses caused by the DBR grating and the determination of the DBR reflectivity. Furthermore, additional losses in the bent DBR-RW lasers caused by the S-bend (i.e. radiation and scattering losses) are quantified by comparing them to the straight DBR-RW lasers. Within the active resonator, the S-bend losses amount to αBend = 0.6 cm−1 (αBend = 0.5 dB) for the smallest manufactured lateral S-bend offset H = 40 μm. For both straight and bent DBR-RW lasers spectrally narrow single-mode emission is obtained. A lateral beam width of 3.8 μm (using second moments) and a lateral far-field angle of about 18° and 19.5° (using second moments) for the straight and S-bend DBR-RW are measured, respectively. This gives a lateral beam propagation ratio of 1.2 and 1.3 (using second moments) for straight and S-bend DBR-RW, respectively. The radiation loss in dependency of the lateral S-bend offset is simulated and compared to experimentally estimated S-bend losses for bent DBR-RW lasers (H = 40 μm, H = 60 μm and H = 70 μm).