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.
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.
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.
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.
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.
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.
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.
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.
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Simran Arora et al 2024 Semicond. Sci. Technol. 39 075009
Pulsed laser deposition technique is used to grow unintentionally n-type (0001)ZnO layers with high crystalline and morphological qualities on p-type (0001)GaN/sapphire templates. Electroluminescent devices are fabricated on these p–n heterojunctions. Oxygen pressure during growth has been found to influence strongly the crystalline and defect properties of the grown layers, which affect not only the current–voltage characteristics but also the emission properties of the electroluminescent devices. It has been observed that the electroluminescence (EL) spectra have both defects related visible and band-edge related ultraviolet (UV) transition features stemming from both GaN and ZnO sides. The study reveals that UV to visible EL intensity ratio maximizes at an optimum oxygen pressure. The relative contribution of EL originating from ZnO and GaN sides can be tuned by the applied bias, as the bias can control the depletion width and hence the carrier interdiffusion across the junction. This finding thus offers a scope to electrically tune the colour of the emitted light in these devices.
Yuechang Sun et al 2024 Semicond. Sci. Technol. 39 075008
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.
Yifan Zhu et al 2024 Semicond. Sci. Technol. 39 075007
The surface of the deep ultraviolet (DUV) photodiodes requires an enhanced light absorption to improve wall-plug efficiency. The resonant Mie scatterer has a high optical mode density with a high refractive index all-dielectric resonant structure, which causes strong light coupling and improves forward scattering, providing a new perspective for efficient light absorption on the surface of the DUV photodiodes. In this work, a method is proposed for the design of nano-optical structures that is capable of supporting forward light scattering across the resonant bandwidth. This is achieved by utilizing intelligent algorithms in conjunction with Maxwell's equations. The results show that the average light absorption coefficient of the optimized optical structure is improved to more than 96% with angle-independent and polarization-independent characteristics. Based on intelligent algorithms, a reverse design approach can be employed to maximize this effect, thereby offering novel avenues for enhancing the wall-plug efficiency of the DUV photodiodes.
Hengbo Liu et al 2024 Semicond. Sci. Technol. 39 075006
Applying the valley contrasting properties of valleytronic materials to logical operations is the foundation of valleytronic device manufacturing. It is predicted that single-layer (SL) 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 (DL) structure (∼80 meV) is much greater than that of the SL structure (∼59 meV) due to the increased magnetic moment of the DL structure, indicating the potential tunable character by stacking few layers. We believe that SL LaCl2 has great potential for device manufacturing and application in the field of valley electronics.
Wun-Ciang Jhang et al 2024 Semicond. Sci. Technol. 39 07LT01
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, long retention time, 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.
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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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Zhang et al
Solid-state UV photodetectors (PD) have received numerous attention because of the advantages of small size, absence of external cooling, high selectivity, and the ability to utilize the energy band structure semiconductor materials to achieve detection across various wavelengths. III-nitride thin films, as typical wide bandgap semiconductors with mature n-type and p-type doping capabilities, are ideal candidates for solid-state UV-PDs. However, a combination between III-nitride and other wide bandgap materials can either enrich the functionality of such devices such as spectrum-selective and broadband UV detection, or offers opportunities to enhance device performance, including high photoresponsivity, high external quantum efficiency, low dark current and fast response time. This topical review focuses on giving a thorough review of the III-nitride based hybrid-type UV photodetectors, their recent progress and future prospects. This review highlights different optical and electrical properties of various materials including GaN, Ga2O3, ZnO, perovskite etc. By carefully choosing the materials on two sides of the heterojunction and modulating the thickness and fermi levels and corresponding layers, p-i-n, Schottky, or MSM type photodetectors were successfully fabricated with outstanding device performances and novel spectral-selective properties. The advantages for future development of such hybrid-type PDs will be discussed, such as inherently formed p-n junction with large depletion region at the interface of two different materials, capability of bandgap engineering to tune the band offset of conduction band and valence band, thus enabling large barrier height for one type of carrier without influencing the other. The drawbacks in hybrid-type UV-PD due to poor interface quality and challenges in forming electrical contact in nanostructure hybrid UV-PD will also be discussed.
Kumar et al
This study focuses on a cost-effective method for fabrication of a metal oxide semiconductor-heterostructure field effect transistor (MOSHFET) based on MgZnO/CdZnO (MCO) using dual ion beam sputtering (DIBS), in contrast to the more expensive epitaxial growth system. The MOSHFETs developed in this research exhibit notable characteristics, such as a such as a substantial two-dimensional electron gas (2DEG) transconductance (~2.6 mS), a high ION/IOFF response ratio in the order of 108, and minimal gate leakage current. Furthermore, we explore the impact of rapid thermal annealing (RTA) on the drain current at various temperatures (600 and 800 ℃). The results indicate a fourfold improvement in drain current compared to unannealed conditions, primarily attributed to reduced contact resistance and no degradation in term of MgZnO/CdZnO structure. Additionally, an analysis of post-RTA treatment under a nitrogen (N2) atmosphere on gate leakage current is presented. The investigation spans temperatures ranging from 400 to 800 ℃, revealing that above 600 ℃ (gate leakage at 400 to 600 ℃ is around ~10-9 A), gate leakage in HFET is augmented by one order of magnitude (~10-8 A) due to a phase change in the dielectric. These findings underscore the feasibility of DIBS-grown MCO MOSHFETs as an economical solution for the mass production of switching devices and sensors.
Netzel et al
Defect-selective etching with molten Ba(OH)2/MgO etch drops was performed on c-plane AlGaN layers covering the entire composition range between GaN and AlN. Regardless of the aluminum content, the etchant produced shallow, hexagonal etch pits with depth-to-diameter ratios of 1/10 – 1/100. Two predominant types of etch pits were observed, which differed in size. In addition, the etch rate decreased from the center to the edge of the area exposed to the etch drops, providing a radially symmetric variation in etch pit size. 
For all AlGaN compositions, the positions of the etch pits correlate perfectly with the positions of the dark luminescence spots in cathodoluminescence measurements. Areas on the AlGaN samples that were not exposed to the etching procedure showed identical dark spots with the same size and density as those in the etched regions. Additionally, the density of etch pits and dark spots corresponded to the density of threading dislocations in the AlGaN layers. 
These observations demonstrate that the density of threading dislocations in c-plane AlGaN layers can be determined by destructive defect-selective etching with Ba(OH)2/MgO and etch pit counting, as well as by nondestructive counting of the dark spots in cathodoluminescence images. 
Sarkar
In this study, we examined the gate leakage characteristics of normally off pGaN/AlGaN/GaN HEMTs through a simulation study. The Fowler Nordheim Tunneling (FNT) mechanism mainly contributes to the gate leakage process as indicated by the TCAD simulation. However, at low bias, the FNT undercalculates the leakage current since the electric field is low in this region. This extra leakage current component at this low bias region can be attributed to the presence of surface traps. Trap-assisted tunneling current along with the FNT current can explain forward leakage characteristics of the pGaN HEMTs. Our TCAD simulations were matched with the experimental data for five devices from four different research groups to support this claim. Using TCAD simulations, we have been able to analyze several device parameters including the various potential drops inside the gate stack structure. We were able to identify some of the trap levels and compare them to the dominant defects expected to be present in the pGaN cap layer. Furthermore, we studied the effects of different device parameters on the gate leakage process in the pGaN HEMT.
Wang et al
To reduce the static power consumption of the NT JLFET and the effect of SCEs on the NT JLFET, A nanotube junctionless field effect transistor with cyclic low doping concentration regions (C NT JLFET) is proposed. Based on Sentaurus TCAD numerical simulations, the electrical properties of the C NT JLFET and the NT JLFET were comparatively investigated, and the effects of the length (LCD) and radius (RCD) of cyclic low doping concentration regions on the electrical properties of the C NT JLFETs were studied. The C NT JLFET reduces the gate-induced drain leakage (GIDL) due to lateral band-to-band-tunneling (L-BTBT) as compared to the NT JLFET. As the LCD or RCD increases, the off-state current decreases. In addition, the C NT JLFET suffers from fewer short channel effects (SCEs), such as threshold voltage roll-off, drain-induced barrier lowering and subthreshold swing deterioration, compared to the NT JLFET. The inhibition of L-BTBT and attenuation of SCEs by cyclic low doping concentration regions remains when the channel length of the C NT JLFET is shortened to 10 nm. The C NT JLFET are suitable for low power applications as they exhibit reduced L-BTBT and suffer from fewer SCEs.
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Anitha Jose et al 2024 Semicond. Sci. Technol. 39 075004
The mean inner potential (MIP), V0, for a series of Zn group VI semiconductor nanostructures were measured experimentally using off-axis electron holography. 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.
Carsten Netzel et al 2024 Semicond. Sci. Technol.
Defect-selective etching with molten Ba(OH)2/MgO etch drops was performed on c-plane AlGaN layers covering the entire composition range between GaN and AlN. Regardless of the aluminum content, the etchant produced shallow, hexagonal etch pits with depth-to-diameter ratios of 1/10 – 1/100. Two predominant types of etch pits were observed, which differed in size. In addition, the etch rate decreased from the center to the edge of the area exposed to the etch drops, providing a radially symmetric variation in etch pit size. 
For all AlGaN compositions, the positions of the etch pits correlate perfectly with the positions of the dark luminescence spots in cathodoluminescence measurements. Areas on the AlGaN samples that were not exposed to the etching procedure showed identical dark spots with the same size and density as those in the etched regions. Additionally, the density of etch pits and dark spots corresponded to the density of threading dislocations in the AlGaN layers. 
These observations demonstrate that the density of threading dislocations in c-plane AlGaN layers can be determined by destructive defect-selective etching with Ba(OH)2/MgO and etch pit counting, as well as by nondestructive counting of the dark spots in cathodoluminescence images. 
Arghyadeep Sarkar 2024 Semicond. Sci. Technol.
In this study, we examined the gate leakage characteristics of normally off pGaN/AlGaN/GaN HEMTs through a simulation study. The Fowler Nordheim Tunneling (FNT) mechanism mainly contributes to the gate leakage process as indicated by the TCAD simulation. However, at low bias, the FNT undercalculates the leakage current since the electric field is low in this region. This extra leakage current component at this low bias region can be attributed to the presence of surface traps. Trap-assisted tunneling current along with the FNT current can explain forward leakage characteristics of the pGaN HEMTs. Our TCAD simulations were matched with the experimental data for five devices from four different research groups to support this claim. Using TCAD simulations, we have been able to analyze several device parameters including the various potential drops inside the gate stack structure. We were able to identify some of the trap levels and compare them to the dominant defects expected to be present in the pGaN cap layer. Furthermore, we studied the effects of different device parameters on the gate leakage process in the pGaN HEMT.
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.
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.