Wide Gap Semiconductor Research Articles

Controllable p- and n-type behaviours in emissive perovskite semiconductors.

Reliable control of the conductivity and its polarity in semiconductors is at the heart of modern electronics1-7,and has led to key inventions including diodes, transistors, solar cells, photodetectors, light-emitting diodes and semiconductor lasers. For archetypal semiconductors such as Si and GaN, positive (p)- and negative (n)-type conductivities are achieved through the doping of electron-accepting and electron-donating elements into the crystal lattices, respectively1-6. For halide perovskites, which are an emerging class of semiconductors, mechanisms for reliably controlling charge conduction behaviours while maintaining high optoelectronic qualities are yet to be discovered. Here we report that the p- and n-type characteristics in a wide-bandgap perovskite semiconductor can be adjusted by incorporating a phosphonic acid molecular dopant with strong electron-withdrawing abilities. The resultant carrier concentrations were more than 1013 cm-3 for the p- and n-type samples, with Hall coefficients ranging from -0.5 m3 C-1 (n-type) to 0.6 m3 C-1 (p-type). A shift of the Fermi level across the bandgapwas observed. Importantly, the transition from n- to p-type conductivity was achieved while retaining high photoluminescence quantum yields of 70-85%. The controllable doping in the emissive perovskite semiconductor enabled the demonstration of ultrahigh brightness (more than 1.1 × 106 cd m-2) and exceptional external quantum efficiency (28.4%) in perovskite light-emitting diodes with a simple architecture.

Effects of mechanical alloying methods on structural phase stability, chemical state, optical, electrical and ferroelectric properties in Sc-doped α-Fe2O3 system

The development of metal doped α-Fe2O3 (hematite) based wide band gap semiconductors with high electrical conductivity, high electrical polarization and wide optical band gap is a challenging problem and also useful for application point of view. In this work, a substantial enhancement of electrical conductivity, optical band gap and ferroelectric polarization have been recorded at room temperature for Sc doped α-Fe2O3 system. Two different methods of the mechanical alloying and subsequent heat treatment have been used to synthesize the samples of α-Fe2-xScxO3 oxide (x = 0.2–1.0). The X-ray diffraction patterns have confirmed formation of single-phased Rhombohedral structure for low Sc doping content (x = 0.2), whereas a mixture of Rhombohedral-structured α-Fe2O3 type phase and cubic-structured Sc2O3 type phase has been formed for the higher Sc contents (x = 0.5 and 1.0). The phase fractions varied depending on the amount of Sc content, chemical reaction during mechanical alloying of the elementary oxides and solid-state reaction during the heat treatment. Response of the Sc2O3 type phase in Raman spectra is sensitive depending on the methods of inter-mixing the α-Fe2O3 and Sc2O3 by mechanical alloying. X-ray photoelectron spectroscopy (XPS) confirmed the metal (Fe, Sc) ions in +3 charge state, although the samples for low Sc content x = 0.2 showed a signature of Fe+2 and Sc+4 states. A detailed analysis of the Fe 3s XPS band confirmed a strong 3s-3d spins exchange coupling of strengths 1.18 eV–1.34 eV.

Controlled Fabrication of Native Ultra‐Thin Amorphous Gallium Oxide From 2D Gallium Sulfide for Emerging Electronic Applications

AbstractOxidation of 2D layered materials has proven advantageous in creating oxide/2D material heterostructures, opening the door for a new paradigm of low‐power electronic devices. Gallium (II) sulfide (β‐GaS), a hexagonal phase group III monochalcogenide, is a wide bandgap semiconductor with a bandgap exceeding 3 eV in single and few‐layer form. Its oxide, gallium oxide (Ga2O3), combines a large bandgap (4.4–5.3 eV) with a high dielectric constant (≈10). Despite the technological potential of both materials, controlled oxidation of atomically‐thin β‐GaS remains under‐explored. This study focuses on the controlled oxidation of β‐GaS using oxygen plasma treatment, addressing a significant gap in existing research. The results demonstrate the ability to form ultrathin native oxide (GaSxOy), 4 nm in thickness, upon exposure to 10 W of O2, resulting in a GaSxOy/GaS heterostructure where the GaS layer beneath remains intact. By integrating such structures between metal electrodes and applying electric stresses as voltage ramps or pulses, their use for resistive random‐access memory (ReRAM) is investigated. The ultrathin nature of the produced oxide enables low operation power with energy use as low as 0.22 nJ per operation while maintaining endurance and retention of 350 cycles and 104 s, respectively. These results show the significant potential of the oxidation‐based GaSxOy/GaS heterostructure for electronic applications and, in particular, low‐power memory devices.

Plasmonic Ag Nanoparticles on SiC for Use as SERS Substrate and in Integrated Optical Sensors for Bio-Chemical Applications

Development of optical chemical sensors for the detection of specific toxic chemicals at ultratrace levels and analysis of complex mixtures is crucial for new green and safe technologies [1, 2]. Metallic structures confined at the nanoscale acquire interesting properties such as strongly localizing E fields on their surfaces through Plasmonic Resonance under stimuli of light at certain wavelengths. This nanostructures are called plasmonic structures [3–5]. This effect is exploited to amplify the optical signal obtained by the molecules of interest, located near plasmonic structures [3, 6]. Purpose of the work is the development of innovative, easy to manufacture and cheap optical active layer consisting of Plasmonic Ag Nanoparticles on a Wide Band Gap semiconductor material such as Silicon Carbide to be used as substrate for Surface Enhanced Raman Scattering or for the fabrication of integrated optical sensor for remote chemical and biological applications. In this contest, the phenomenon of Ag thin film thermal dewetting on SiC substrate was implemented to develop a simple nanoparticles synthetic approach. Scanning Electron Microscopy confirmed the formation of Ag nanoparticles by thermal annealing of thin silver film. 4-MBA was used as probe molecule for SERS phenomenon investigation. The formation of a covalent bond between the silver nanostructures, acting as plasmonic "hot spots", and the species of interest enable its detection at very low concentrations, in the range of 10-5 M or less, in both Raman and UV-Vis configurations.

Up-conversion luminescence and Bi SPR effect promoted Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst for efficient photocatalytic hydrogen production with simultaneous degradation of malachite green

Photocatalytic hydrogen production with simultaneous degradation of organic pollutants by using solar energy provide a promising strategy to solve the energy and environmental issue in the future. However, for onefold wide band-gap semiconductor, the poor photocatalytic efficiency limits its application on a large scale due to its easy recombination of photo-generated electron-hole pairs and low solar energy utilization. Herein, a novel Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst is prepared via photo-assisted isoelectric point method. In this composite photocatalyst, up-convention luminescence material, NaYF4:Er,Yb,Tm, can offer more ultraviolet light and visible light to intensify the activations of BiOBr and metal Bi nanoparticles, respectively. Furthermore, the formation of Z-scheme BiVO4(040)-BiOBr photocatalystic sytem, the spatial separation of the BiVO4(040) and BiVO4(110) facets and the presence of metal Bi surface plasmon resonance effect are contributed to the high-efficiency separation of the photo-generated electron-hole pairs. The experimental results show that as-prepared Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst exhibits advanced photocatalytic hydrogen production amount (192.0 μm) and excellent degradation ratio of malachite green (88.51 %) under simulated sunlight irradiation for 5.0 h. The apparent quantum yield of the Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst at 420 nm reaches a specific value of 5.8 %. In addition, Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst also remains a high stability in the photocatalytic hydrogen production with simultaneous degradation of malachite green within six reuse. At last, the possible reaction mechanism and degradation pathways of malachite green caused by Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst under simulated sunlight irradiation are put forward.

Thermal cycling characterization of an integrated low-inductance GaN eHEMT power module

To exploit the potential of wide-bandgap semiconductors in high-frequency applications, innovative packaging designs are developed to minimize the parasitic inductance of power modules. This study presents an integrated power module with a hybrid PCB/DBC structure, which uses top-side cooling prepackaged GaN enhancement-mode high-electron-mobility transistors. The module achieves a remarkably low parasitic inductance of 2.65 nH. However, there is relatively scarce research on the reliability of this heterostructure, particularly its sensitivity to thermomechanical stress due to the coefficients of thermal expansion mismatch among material interfaces. In this work, the thermal cycling characteristics of the integrated power module are comprehensively investigated. Electrical and thermal parameters were periodically and separately measured offline on a simplified package to monitor the health conditions and decouple possible synergy and competition effects among the failure modes from all packaging components. A thorough failure analysis was conducted using nondestructive visual inspections and scanning acoustic microscopy, complemented by destructive cross-sectional examination and scanning electron microscopy. The findings identified the delamination of the DBC upper copper layer, which exhibited a conchoidal fracture interface, as the primary factor that contributed to the failure of the power module with increased thermal resistance. Furthermore, the study dissected its initiation and propagation mechanisms. This investigation provides valuable insights for the development of more reliable low-inductance power module designs.

Impurity Level-Induced Broadband Photoelectric Response in Wide-Bandgap Semiconductor SrSnO3.

Broadband spectrum detectors exhibit great promise in fields such as multispectral imaging and optical communications. Despite significant progress, challenges like materials instability in such devices, complex manufacturing process, and high cost still hinder their further application. Here, we present a method that achieves broadband spectral detection by impurity-level in SrSnO3. We report over 500 mA/W photoresponsivity at 275 nm (ultraviolet C solar-bind) and 367 nm (ultraviolet A) and ∼60 mA/W photoresponsivity at 532 and 700 nm (visible) with a voltage bias of -5 V. Further transport and photoluminescence results reveal a new phase transition at 88 K, which would significantly affect the impurity level of the La-doped SrSnO3 film, indicating that the broadband response attributes to the impurity levels and mutual interactions. Additionally, the photodetector demonstrates excellent robustness and stability under repeated tests and prolonged exposure in air. These findings show the potential of SrSnO3 as a material for photodetectors and propose a method to achieve broadband spectrum detection, creating new possibility for the development of single-phase, low-cost, simple structure, and high-efficiency photodetectors.

Characteristics of 2N4416 Si JFETs for radiation spectrometer charge sensitive preamplifiers

The input transistors (JFETs) of feedback resistor-less charge sensitive preamplifiers (CSPs), for photon and charged particle counting radiation spectrometers, that use semiconductors as their detectors, are operated in an unusual forward biased mode; consequently, manufacturer datasheets cannot necessarily be relied upon, as they do not specify the characteristics of the JFETs when they are operated with the gate-to-source junction forward biased. This experimental study, in which 165 2N4416 and 2N4416A NJ26 silicon junction field effect transistors (JFETs) were electrically characterised at ambient laboratory temperature, focused on the JFETs’ performances in the context of their use as input transistors of feedback resistor-less charge sensitive preamplifiers (CSPs). The experimental study found evidence which supports much of the common practice of the skilled CSP designer but which had not been documented with results in the open literature until now. This includes, inter alia, that: the 2N4416 performs better than the 2N4416A; not all transistors even of the same type have comparable performance when operated in forward bias mode; only a small proportion of 2N4416 and 2N4416A transistors are of desirable performance characteristics for CSPs; and, individual screening of each candidate JFET is required if an optimally performing CSP is to be produced – even when using JFETs of the same type from the same batch. The methodology and analysis documented here will also be useful to researchers developing new wide bandgap semiconductor JFETs for high temperature tolerant and radiation-hard CSPs.

Ultrathin 2D/2D ZnIn2S4/La2Ti2O7 nanosheets with a Z-scheme heterojunction for enhanced photocatalytic hydrogen evolution.

Layered lanthanum titanate (La2Ti2O7) perovskite is a good photocatalytic material owing to its high stability, strong redox ability, and non-toxicity. However, its inherent wide bandgap limits its application in photocatalytic hydrogen evolution. Therefore, combining La2Ti2O7 with two-dimensional (2D) narrow-bandgap semiconductors to form 2D/2D layered structures is the preferred strategy to improve its photocatalytic performance. In this study, a novel 2D/2D ZnIn2S4/La2Ti2O7 Z-scheme heterojunction was prepared through a solvothermal method. The experimental results show that when the molar ratio of La2Ti2O7 to ZnIn2S4 is 1 : 4, the hydrogen evolution rate of the composite under ultraviolet-visible light reaches 6.97 mmol g-1 h-1, which is 3.5 times higher than that of the pure ZnIn2S4. The results of the morphological characterization studies of the samples and the photoelectrochemical measurements show that channels for the rapid transfer of carriers are generated by the unique 2D/2D structure of these samples, and the separation and migration efficiency of the photogenerated carriers significantly improved due to the formation of the Z-scheme heterojunction. This study provides useful insights into the modulation of wide-bandgap semiconductors and research into solar energy conversion.

Structural, wide band gap half-metallic, and pressure-dependent thermodynamic predictions of Li2TMMgO6 (TM = V, Nb, and Ta) double perovskites.

Li2VMgO6, Li2NbMgO6, and Li2TaMgO6 double perovskite compounds were energetically the most stable in the FM phase. The lattice constants were 7.63Å, 7.94Å, and 7.95Å, and the Curie temperatures were 910.451K, 930.739K, and 1258.821K, respectively. The wide bandgap semiconductor characters were provided in the GGA-PBE methods as 2.139eV, 4.209eV, and 5.007eV, respectively. This wide band gap semiconductor state in the majority carriers and the metallic state in the minority states made these double perovskites true half-metallic ferromagnetics. The bulk modulus obtained in the ground state calculations and the values obtained from thermodynamic calculations were relatively close. Debye temperatures in the initial state conditions were 747K, 685.13K, and 587.77K, respectively. The total magnetic moment values were calculated as 3.00 µB/f.u. The most significant contribution to this value came from oxygen atoms. The theoretical calculations of Li2VMgO6, Li2NbMgO6, and Li2TaMgO6 double perovskite alloys were performed using the WIEN2k program developed by Blaha et al. The electronic calculations were made with GGA-PBE, GGA + mBJ, and GGA + U approximations in the space number 225 and the Fm-3m symmetry group. The thermodynamic calculations were performed using Gibbs2. In thermodynamic calculations, temperature increases were determined as 100K and temperature values were increased from 0 to 1200K.

Improving the efficiency and stability of betavoltaic batteries based on understanding efficiency fluctuations and gaps with theoretical limits

Wide-bandgap semiconductors are regarded as preferred materials for preparing semiconductor conversion devices in betavoltaic batteries due to their high theoretical conversion efficiency (ηc). However, there are a few comprehensive analytical studies on why the experimental values of ηc are generally much lower than the theoretical limit of ηc (ηc-limit) and how to improve ηc and its stability. In this work, combined with the energy deposition distributions of Ti3H2, 63Ni, and 147Pm2O3 radioactive sources in SiC obtained from Monte Carlo simulations, a multi-physical mechanism, multi-parameter coupling numerical model was established. This model can comprehensively analyze the output characteristics of betavoltaic batteries under the influence of actual device structural and material parameter changes. Our results show that changes in structural and material parameters cause significant variations in the collection efficiency (Q) of the radiation-generated electron–hole pair (RG-EHP). Considering structural parameters are easy to control, instabilities in actual SiC material parameters, which include electron diffusion length (Ln), hole diffusion length (Lp), and surface recombination velocity (S), are the main reason that ηc fluctuates significantly and is generally far lower than ηc-limit. Due to differences in the distribution of RG-EHP produced by different radioactive sources in SiC, the dominant parameters causing ηc fluctuations differ. By analyzing differences in recombination loss mechanisms under different radioactive sources, the device structures were designed in a targeted manner to make ηc closer to ηc-limit. Meanwhile, when the SiC material quality fluctuates, the stability of ηc increases by 58.5%, 35.3%, and 48.2% under Ti3H2, 63Ni, and 147Pm2O3, respectively.

An Aerosol-Assisted Chemical Vapor Deposition Route to Tin-Doped Gallium Oxide Thin Films with Optoelectronic Properties.

Gallium oxide is a wide-bandgap compound semiconductor material renowned for its diverse applications spanning gas sensors, liquid crystal displays, transparent electrodes, and ultraviolet detectors. This paper details the aerosol assisted chemical vapor deposition synthesis of tin doped gallium oxide thin films using gallium acetylacetonate and monobutyltin trichloride dissolved in methanol. It was observed that Sn doping resulted in a reduction in the transmittance of Ga2O3 films within the visible spectrum, while preserving the wide bandgap characteristics of 4.8 eV. Furthermore, Hall effect testing revealed a substantial decrease in the resistivity of Sn-doped Ga2O3 films, reducing it from 4.2 × 106 Ω cm to 2 × 105 Ω cm for the 2.5 at. % Sn:Ga2O3 compared to the nominally undoped Ga2O3.

EFFECT OF SNO2 POROUS STRUCTURE ON ITS OPTICAL AND PHOTOELECTROCHEMICAL PROPERTIES IN WATER AND WATER-METHANOL SOLUTIONS

Tin(IV) oxide is a wide-gap semiconductor material that is widely used in photooxidation reactions of organic compounds. However, the relationship between energetic and photoelectrocatalytic properties in the oxidation of small organic molecules has not yet been sufficiently explored. In this work, a series of tin oxides were synthesized using hydrothermal, sol-gel, and template methods. Polystyrene spheres with a size of 250 nm, as well as cetyltrimethylammonium bromide, were used as templates. X-Ray diffraction, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy and diffuse reflectance spectroscopy methods were used to study the structure, surface composition, optical and energy characteristics. Using photoelectrochemical methods, the potentials of the conduction band and valence band were determined, and photocurrents in aqueous and aqueous-methanol solutions were studied depending on electrode polarization. It is shown that the preparation method (sol-gel or hydrothermal) does not affect the position of energy bands, while the use of a template during synthesis leads to an increase in the average pore diameter in the samples and an increase in photocurrent values in the presence of methanol. It has been established that for template-synthesized samples, the magnitude of photocurrents in a water-methanol mixture increases with an increase in the valence-band potential. The sample prepared by the hydrothermal method using a template showed the highest photocurrent values both in the background electrolyte (17.3 μA/cm2) and in the presence of methanol (26 μA/cm2), compared to the sample prepared without using a template in the electrolyte with the addition of methanol (7.6 μA/cm2) and without it (7.8 μA/cm2).

Schottky-Barrier-Free Plasmonic Photocatalysts for Solar-Driven Ammonia Synthesis

Ammonia is not only an indispensable feedstock to produce essential industrial chemicals like fertilizers, but it is also a potential hydrogen energy carrier owing to its high energy density and hydrogen capacity. Currently, most ammonia required for humans comes from the Haber–Bosch process, which contributes more than 90% of the annual global ammonia output. However, the harsh reaction conditions of this process result in serious energy and environmental issues. According to the relevant statistics, the ammonia industry consumes about 2% of the total energy and generates about 1.6% of the total CO2 emission annually in the world.It is therefore crucial to develop a green and sustainable strategy for ammonia synthesis. Among various alternative technologies of the Haber–Bosch process, artificial photosynthesis has attracted wide research interests and has been regarded as a promising, environmentally friendly, and energy-saving process. Photocatalytic ammonia synthesis can utilize renewable solar energy to drive the reaction and operate under mild conditions, which possesses the benefits of the simple reaction system, low cost, and safety. Although numerous photocatalysts have been explored over the past several decades, their activity and efficiency have still been low and far from the practical application requirements. It is therefore a huge challenge to design efficient photocatalysts for ammonia synthesis.Localized surface plasmon resonance (LSPR) has recently drawn enormous attention. LSPR can not only endow plasmonic nanomaterials with large absorption cross-sections and intense local field enhancement but also generate energetic hot electrons and hot holes. Owing to the appealing features of LSPR, plasmonic photocatalysis has shown great potential in ammonia synthesis. Plasmonic photocatalysts are usually composed of noble metals and wide bandgap semiconductors. However, the Schottky barrier will form at the metal–semiconductor interface in such hybrid structures due to the mismatch of the band structures between plasmonic metals and semiconductors. Hence, a large portion of the hot electrons cannot cross the Schottky barrier and get lost in the metal through the recombination with the holes. To overcome the drawbacks caused by the Schottky barrier, it is strongly desirable to develop a new type of plasmonic semiconductor photocatalysts, i.e., Schottky-barrier-free plasmonic photocatalyst.The Schottky-barrier-free plasmonic photocatalysts are usually degenerately doped semiconductors containing lattice oxygen vacancies. They possess high free electron densities and strong plasmon resonance because of the high-level doping, which results in abundant hot charge carriers upon plasmon excitation. Moreover, they also have appropriate surface sites that can adsorb reactant molecules and activate them. The photogenerated plasmonic hot charge carriers can get trapped at the defect sites and thereafter drive redox reactions. Compared with traditional metal–semiconductor hybrid plasmonic photocatalysts, Schottky-barrier-free plasmonic photocatalysts enable hot charge carriers to be transported nearly freely in the material, resulting in high charge utilization and photocatalytic efficiency.We have demonstrated the synthesis of Schottky-barrier-free plasmonic MoO3−x nanospheres (NSs) with remarkably high oxygen vacancy (OV) contents by aerosol-spray. The MoO3−x NSs can achieve efficient ammonia photosynthesis through a “killing two birds with one stone” mechanism. On the one hand, the OVs can serve as chemisorption sites for N2 molecules and participate in their activation. On the other hand, the introduction of OVs generates a large number of free electrons near the conduction band, which induces a broad absorption band from the visible to the NIR region owing to the plasmon resonance. The Schottky-barrier-free nature of this plasmonic semiconductor allows free transportation of the plasmonic hot charge carriers, while the defect states introduced by the OVs can effectively trap the hot electrons to prevent rapid electron–hole recombination. As expected, the as-prepared material exhibits a superior ammonia production rate, with the highest apparent quantum efficiency (AQE) of 1.24% at 808 nm and an appreciable solar-to-ammonia conversion efficiency (SACE) of 0.057% for NH3 production. Besides MoO3−x , WO3−x is also an excellent candidate for Schottky-barrier-free plasmonic photocatalysts. We have synthesized square WO3−x nanoplates hydrothermally. The WO3-x nanoplates possess regular morphology, wide light absorption, and great ammonia production performance. Furthermore, by introducing doping elements (Mo, V, Fe, Bi) into WO3−x nanoplates, the N2 activation and dissociation can be improved by refining the defect states. The Mo-doped WO3−x nanoplates exhibit the highest ammonia production rate of 145.50 μmol g−1 h−1 with SACE of 0.011% since the Mo species can promote the chemisorption and polarization of N2 molecules and significantly reduce the reaction barrier. Notably, Mo-doped WO3−x nanoplates are a dual-function photocatalyst that can oxidize water to hydrogen peroxide in a stoichiometric ratio while synthesizing ammonia. Figure 1

(Invited) The Evolving SiC Market and Impact on CMP Supply Chain

Silicon carbide (SiC) is a wide bandgap semiconductor with physical and electrical properties that provide superior performance in high-voltage or high-power applications. Compared to the more established silicon devices, SiC provides better thermal conductivity, ~10x higher breakdown voltage, faster switching speeds and lower resistivity. Even with the performance advantages, the adoption rate of SiC is slowed by high cost and the inherent difficulty of processing this material. SiC is extremely hard (just below diamond on the hardness scale) and chemically inert which makes processing boules into wafers rather difficult. This presentation will contrast some of the basic differences between process methods developed for silicon and other semiconductor materials versus those required for SiC.Demand for high-quality single crystal SiC substrates continues to rise as the worldwide demand for electric vehicles, charging infrastructure, green energy production, and more efficient power devices in general requires more and more SiC devices. SiC wafer manufacturers are trying to ramp output as quickly as possible but technical difficulties of processing SiC are often a limiting factor. In spite of aggressive capital spending by many of the major players, the actual growth in substrate production has been constrained to around 15% CAGR even though demand would support a much faster ramp. As end use markets continue to evolve, ripple effects are also evident in the underlying supply chains, such as CMP pads and slurries.

SiC CMP Process Sensitivities

Single-crystal silicon carbide (SiC) is a wide bandgap semiconductor with physical and electrical properties that provide superior performance compared to silicon or almost any other semiconductor material in high-voltage and high-power applications. It is also extremely hard, second only to diamond, and chemically almost inert which makes the CMP process step quite challenging. In recent years, a great deal of effort has been expended on advancing this process, particularly with regard to slurry formulations that can provide reasonable removal rates and damage-free final surface finishes. In this presentation, we will review a number of these developments for SiC CMP slurries. We will present data highlighting their process responses to standard CMP parameters, interactions with pad conditioning, and describe some of the requirements for production process controls.

(Electronics and Photonics Division Award) Research Advances Wide- and Ultrawide-Bandgap Power Switching Devices

Wide bandgap semiconductors such as SiC and GaN (WBG) and emerging ultrawide-bandgap materials such as Ga2O3, AlGaN, and Diamond (UWBG) represent the next-generation materials for high performance medium voltage and high voltage power switch technology. Such devices have a wide range of immediate Naval applications, including high-power satellite communications and radar, unmanned underwater and aerial vehicles, ship drive components, and hybrid vehicle inverters. Vertical SiC power device technology has matured rapidly over the past two decades, owing to advances in substrates, a fundamental understanding of epitaxial growth to eliminate performance-limiting defects, as well as device design breakthroughs. This has enabled breakthroughs in highly integrated module design for medium voltage power conversion with switching frequency >100 kHz. In parallel, lateral GaN-based high electron mobility transistor (HEMT) technology has been highly successful for RF power amplifiers and is well positioned to supersede GaAs-based microwave circuits. Recently, GaN-based vertical and lateral power devices have attracted significant interest due to promising device results coupled with progress in native substrate, epitaxial growth, and processing technology developments. This seminar will present an overview of the WBG/UWBG power device efforts at NRL. This research has four primary focus areas – 1) thermal management in III-N power device structures by diamond thin film integration, 2) characterization of substrate materials and homoepitaxial layers used for drift regions of power devices identify appropriate specifications and benchmark performance, 3) process module development, particularly for selective area doping by ion implantation, and 4) pilot production manufacturing of 1.2kV-class PiN diodes including reliability assessments to identify and mitigate performance limiting defects.

(Invited) Tackling Interface Challenges for Shallow Diamond Color Centers

Spin defects in wide-bandgap semiconductors, such as color centers in diamond, can be highly sensitive to local (nanoscale) changes in magnetic field, temperature, and strain. These solid-state quantum sensors have certain advantages over their atomic counterparts owing to their room-temperature operation without the need for vacuum components and the relative ease of photonic- and RF-component integration. However, near-surface quantum defects exhibit spin decoherence and most of the light emitted is trapped within the bulk crystal due total internal reflection at the interface. In this presentation, I will summarize our recent work towards better understanding and addressing these interface challenges, including the modeling and experimental characterization of radiative emission of near-surface emitters, design of nanophotonic components to improve light extraction, and surface analysis and chemical termination techniques aimed at improving spin coherence of emitters.

(Electronics and Photonics Division Poster Award Winner) A High Breakdown Voltage Silicon Carbide (SiC)/Gallium Oxide (Ga2O3) Heterojunction Diode for High Power Applications

Wide and ultrawide bandgap semiconductors demonstrate exceptional performance due to their elevated energy bandgap. This characteristic results in breakdown electric fields surpassing those found in conventional silicon electronics by more than an order of magnitude. Furthermore, the high energy bandgap offers distinctive advantages, including enhanced efficiency, drift velocity, increased voltage blocking, and high-frequency switching, making these semiconductors crucial in pushing the boundaries of electronic technology. Gallium Oxide and Silicon Carbide, distinguished by their unique properties, contribute significantly to the advancement of power electronics. Gallium Oxide, with its wide bandgap of 4.6 – 4.9 eV and excellent thermal stability, stands out for its ability to handle high electric fields and temperatures. Silicon Carbide, on the other hand, boasts a robust combination of high thermal conductivity and a wide bandgap of 3.26 eV, making it well-suited for high-power and high-temperature applications. The combination of these two materials in a heterojunction holds promise for the development of high-performance power devices. In this study, we propose a novel high breakdown voltage Silicon Carbide (SiC)/ Gallium Oxide(Ga2O3) heterojunction diode through TCAD Sentaurus. We present a comparative study of the breakdown voltage and electric field across different heterojunction lengths and under various doping concentrations. The investigated heterojunction showcases a high breakdown voltage of 1899V, making it a promising candidate for advanced power electronics applications. Furthermore, simulation results revealed a significant increase in the breakdown voltage of the SiC/Ga2O3 heterojunction, escalating from 1899 V to 4864 V when extending the heterojunction length. Improved specific ON resistance (RON, sp) and Baliga figure-of-merit (BFOM) will also be presented.

(Invited) Wide Bandgap Semiconductor Homo- and Hetero-P-N Junctions

Wide bandgap (WBG) semiconductors, such as gallium nitride (GaN), gallium oxide (Ga2O3), aluminum nitride (AlN), and diamond, hold immense promise for power electronics applications by drastically reducing power loss, enhancing switching frequency, and reducing system volume. However, effective doping (p-type or n-type) remains a substantial challenge for these materials, given that the p-n junction is a fundamental building block for device design. Selective-area doping, crucial for high-performance electronic devices and integrated circuits, poses another significant obstacle.We report recent progress on selective-area doping for GaN homo-p-n junctions. Although GaN shows substantial development in both p-type and n-type doping, achieving selective doping, especially p-type, remains challenging through techniques such as ion implantation, diffusion, or in-situ doping. Our investigation delves into the challenges of p-GaN regrowth using metal-organic chemical vapor deposition (MOCVD). Interface contaminants post etching and regrowth, such as silicon (Si), carbon (C), and oxygen (O), have been systematically investigated. An optimized interface treatment has been identified to effectively reduce surface charge and, consequently, reverse leakage current to the level comparable to the as-grown p-n junction. Additionally, a novel hydrogen plasma treatment has been proposed to realize selective doping for GaN, successfully applied to p-GaN gated high electron mobility transistors (HEMTs) to improve the dynamic performance by avoiding the etching damage and edge termination for vertical GaN p-n diodes to realize high breakdown voltage.β-Ga2O3 has emerged as a standout in power electronics applications, surpassing Si (3000×), SiC (10×), and GaN (4×) in Baliga’s figure of merit. Its great potential for mass production, facilitated by the availability of high-quality and large-size wafers, significantly enhances its attractiveness. However, challenges, including the absence of p-type doping due to deep acceptor states and a flat valence band, as well as exceptionally low thermal conductivity, limit its performance at high power and temperatures. Overcoming these challenges necessitates hetero-integration with semiconductors possessing p-type characteristics and high thermal conductivity. P-type diamond stands out due to its exceptional thermal conductivity, high critical breakdown field, and well-established p-type characteristics. Moreover, since the n-type doping of diamond also poses challenges, fusing the p-type diamond and n-type Ga2O3 to create a diamond/Ga2O3 p-n-heterojunction can effectively overcome doping bottlenecks for both materials. Our successful construction of a diamond/β-Ga2O3 hetero-p-n junction through the mechanical integration of bulk p-type diamond and bulk n-type Ga2O3 presents robust electrical performance up to 125 ℃, with hysteresis lower than 0.7 V @ 1 μA. Impressively, the ideality factor of the p-n junction is remarkably low at 1.28, and the rectification ratio exceeds 108. This approach has also been applied to other hetero-p-n junctions, such as the diamond/GaN structure, demonstrating consistent robust performance. These findings underscore the significant potential of the mechanical integration approach, offering a promising avenue to simplify the fabrication process and facilitate the widespread application of WBG heterojunctions.