Substrate Resistance Research Articles

When anthraquinone dyes meet pillared montmorillonite: Stability or fading upon exposure to light?

Hybrid pigments have attracted great interest due to their stability and physicochemical properties that can be used in paintings, artworks and in the field of cultural heritage. The study of new materials includes the search for new pigments by immobilization of the dyes in resistant substrates such clays minerals to get new colour fonts and materials with high stability. Organic-inorganic based lake pigments, at different pH, have been prepared. Ti- and Al-pillared montmorillonite were synthesized and loaded with carminic acid (CA) and alizarin (Aliz) organic dyes. The pillaring process was investigated by X-ray diffraction, textural analysis, transmission electronic microscopy and solid state nuclear magnetic resonance of 27Al. The interactions between the organic guest and the inorganic host were highlighted by infrared, 13C and 27Al solid state magnetic nuclear resonance and time resolved fluorescence spectroscopies. The spectra support complex formation between the chromophores and the inorganic matrix. The colours of the pigments prepared were pH dependent. Lake pigments based on Al-Pillared Mt were more stable under light than Ti-based hybrid, even in oil painting formulations.

Dispersal-competition tradeoff in microbiomes in the quest for land colonization

Ancestor microbes started colonizing inland habitats approximately 2.7 to 3.5 billion years ago. With some exceptions, the key physiological adaptations of microbiomes associated with marine-to-land transitions have remained elusive. This is essentially caused by the lack of suitable systems that depict changes in microbiomes across sufficiently large time scales. Here, we investigate the adaptive routes taken by microbiomes along a contemporary gradient of land formation. Using functional trait-based metagenomics, we show that a switch from a microbial ‘dispersal’ to a ‘competition’ response modus best characterizes the microbial trait changes during this eco-evolutionary trajectory. The ‘dispersal’ modus prevails in microbiomes at the boundary sites between land and sea. It encompasses traits conferring cell chemosensory and motile behaviors, thus allowing the local microbes to exploit short-lived nutritional patches in high-diffusion microhabitats. A systematic transition towards the ‘competition’ modus occurs progressively as the soil matures, which is likely due to forces of viscosity or strain that favor traits for competition and chemical defense. Concomitantly, progressive increases in the abundances of genes encoding antibiotic resistance and complex organic substrate degradation were found. Our findings constitute a novel perspective on the ecology and evolution of microbiome traits, tracking back one of the most seminal transitions in the evolutionary history of life.

Fabrication of iron-doped titanium dioxide quantum dots/molybdenum disulfide nanoflower for ethanol gas sensing

In this paper, a high-performance ethanol sensor based on iron (Fe)-doped titanium dioxide (TiO2)/molybdenum disulfide (MoS2) nanocomposite was demonstrated. Flower-like MoS2 and Fe-TiO2 quantum dots (QDs) were synthesized by a facile hydrothermal route, and the Fe-TiO2/MoS2 composite was prepared via layer-by-layer (LbL) self-assembly technique. The Fe-TiO2/MoS2 film sensor was fabricated on a flame resistant (FR-4) epoxy substrate with interdigital electrodes. The microstructure, elementary composition, and morphology of the as-prepared samples were fully characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). The gas sensing properties of the Fe-TiO2/MoS2 film sensor were determined at room temperature upon exposure to different concentration of ethanol gas. The experimental results illustrated that high response, short response/recovery time, stable repeatability, excellent selectivity long-term stability, and a detection limit of low ppb level was achieved by the Fe-TiO2/MoS2 sensor. The underlying sensing mechanism of the Fe-TiO2/MoS2 sensor toward ethanol is explored through systematically experimental investigation combining with first-principle density-functional theory (DFT) simulations. The enhanced ethanol sensing properties were ascribed to the Fe3+ ion doping, and p-n heterojunctions created at interfaces of n-type Fe-TiO2 and p-type MoS2.

Electron concentration in highly resistive GaN substrates co-doped with Si, C, and Fe

Electron concentration in highly resistive GaN substrates with intentional iron (Fe) dopants as well as unintentionally incorporated silicon (Si) and carbon (C) dopants has been investigated. Si, C, and Fe atomic concentrations were 2 × 1017, 1 × 1016, and 1 × 1019 cm−3, respectively as measured by secondary ion mass spectroscopy (SIMS). Temperature dependence of current–voltage (I–V) characteristics revealed that the resistivity (ρ) was 3.8 × 109 Ω cm at 300 K and monotonously decreased to 3.1 × 104 Ω cm at 570 K, giving an activation energy of 0.63 eV. Electron concentration (n) was modeled using analytical equation assuming three impurity levels of Si donor, C and Fe acceptors. The n of 5.0 × 107 and 3.1 × 1012 cm−3 at 300 and 570 K, respectively, with an effective activation energy of 0.60 eV, were derived based on the model. These calculated electron concentration values are in good agreement with the experimental results. In addition, quantitatively analyzed results revealed that around 2 orders of magnitude reduction of n is expected by increasing doping concentration of Fe from 1.0 × 1018 to 1.0 × 1020 cm−3.

Simulation-Based Sensitivity Analysis of Conduction and Switching Losses for Silicon Carbide Power MOSFETs

The behavior of silicon carbide power MOSFETs is analyzed using TCAD device simulations with respect to conduction and switching losses. Device designs with varying breakdown voltages are simulated. The contributions to the on-state resistance are shown at room and elevated temperature. Whereas channel and substrate resistance dominate at low breakdown voltages, drift and JFET resistance dominate at high breakdown voltages. With increasing temperature, the channel resistance decreases and thus the drift resistance is the main contributor already at medium breakdown voltages. Manufacturing processes of a device can have a high influence on its losses. Variations in interface mobility, drift doping, and p-body doping can lead to a significant change of on-resistance, internal capacitances, and reverse recovery charge. For higher voltage classes the drift layer properties should be of major interest as it influences on-resistance and reverse recovery charge.

Effect of multilayered CoO-CoAl2O4 films on improving solar absorptance of Co-WC solar selective absorbing coatings

The multilayered CoO-CoAl2O4 solar selective films were prepared on Co-WC coatings with different mole ratio of Co and Al by sol-gel process. The thin film has high and low refractive indices, respectively. The inner layer can improve surface condition of Co-WC coating as a high absorbing film and buffer lay, annealed at 650 °C in vacuum. The outer layer was annealed at the same condition. The absorptance (α) of the multilayer structure coating increased from 0.873 to 0.932. The properties of the sols were characterized by thermogravimetry-differential scanning calorimetry (TG-DSC). The phase compositions and structure of samples annealed at 650 °C were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure and elements distribution of thin films were investigated by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometer (EDS), respectively. The absorptance of coatings indirectly indicate the binding force between the Co-WC substrate, durability, long-time stability and corrosion resistance are fine. The results illustrated that defects on surface of the Co-WC coating gradually decrease with the deposition of sol films. And the good element gradients in multilayer structures and the structure of thin films might be the reasons for its improvement in absorptance.

Optimization of Graphene Conductive Ink with 73 wt% Graphene Contents.

With the pace of development accelerating in printed electronics, the fabrication and application of conductive ink have been brought into sharp focus in recent years. The discovery of graphene also unfolded a vigorous research campaign. In this paper, we prepared graphene conductive ink and explored the feasibility of applying the ink to flexible paper-based circuit. Since experimental study concentrating upon ink formulation was insufficient, orthogonal test design was used in the optimization of preparation formula of conductive ink for the first time. The purpose of this study was to determine the effect of constituent dosage on conductivity of graphene conductive ink, so as to obtain the optimized formula and prepare graphene conductive ink with good conductivity. Characterization of optimized graphene conductive ink we fabricated showed good adhesion to substrate and good resistance to acid and water. The graphene concentration of the optimized ink reached 73.17 wt% solid content. Particle size distribution of graphene conductive ink was uniform, which was about 1940 nm. Static surface tension was 28.9 mN/m and equilibrium contact angle was 23°, demonstrating that conductive ink had good wettability. Scanning Electron Microscope (SEM) analysis was also investigated, moreover, the feasibility of lightening a light-emitting diode (LED) light was verified. The graphene conductive ink with optimized formula can be stored for almost eight months, which had potential applications in flexible paper-based circuit in the future.

Reliability analysis of BiCMOS SiGe:C technology under aggressive conditions for emerging RF and mm-wave applications: proposal of reliability-aware circuit design methodology

AbstractIn this contribution, the impact of extreme environmental conditions in terms of energy-level radiation of protons on silicon–germanium (SiGe)-integrated circuits is experimentally studied. Canonical representative structures including linear (passive interconnects/antennas) and non-linear (low-noise amplifiers) are used as carriers for assessing the impact of aggressive stress conditions on their performances. Perspectives for holistic modeling and characterization approaches accounting for various interaction mechanisms (substrate resistivity variations, couplings/interferences, drift in DC and radio frequency (RF) characteristics) for active samples are down to allow for optimal solutions in pushing SiGe technologies toward applications with harsh and radiation-intense environments (e.g. space, nuclear, military). Specific design prototypes are built for assessing mission-critical profiles for emerging RF and mm-wave applications.

Penetrating cations induce pleiotropic drug resistance in yeast

Substrates of pleiotropic drug resistance (PDR) transporters can induce the expression of corresponding transporter genes by binding to their transcription factors. Penetrating cations are substrates of PDR transporters and theoretically may also activate the expression of transporter genes. However, the accumulation of penetrating cations inside mitochondria may prevent the sensing of these molecules. Thus, whether penetrating cations induce PDR is unclear. Using Saccharomyces cerevisiae as a model, we studied the effects of penetrating cations on the activation of PDR. We found that the lipophilic cation dodecyltriphenylphosphonium (C12TPP) induced the expression of the plasma membrane PDR transporter genes PDR5, SNQ2 and YOR1. Moreover, a 1-hour incubation with C12TPP increased the concentration of Pdr5p and Snq2p and prevented the accumulation of the PDR transporter substrate Nile red. The transcription factor PDR1 was required to mediate these effects, while PDR3 was dispensable. The deletion of the YAP1 or RTG2 genes encoding components of the mitochondria-to-nucleus signalling pathway did not prevent the C12TPP-induced increase in Pdr5-GFP. Taken together, our data suggest (i) that the sequestration of lipophilic cations inside mitochondria does not significantly inhibit sensing by PDR activators and (ii) that the activation mechanisms do not require mitochondria as a signalling module.

Process and Formulation Strategies to Improve Adhesion of Nanoparticulate Coatings on Stainless Steel

The use of ceramic nanoparticles in coatings can significantly improve their mechanical properties such as hardness, adhesion to substrate, and scratch and abrasion resistance. A successful enhancement of these properties depends strongly on the coating formulation used, and the subsequent structure formed during coating. The aim of the present work was to enhance the adhesion between nanoparticulate coatings and stainless-steel substrates. A covalent particle structure was formed and better mechanical properties were achieved by modifying alumina nanoparticles, as well as substrates, with 3-aminopropyltriethoxysilane and by using a formulation consisting of solvent, modified particles, and bisphenol-A-diglycidylether as cross-linking additive. In addition to the adhesion force needed to remove the coating from the substrate, the type of failure (adhesive or cohesive) was characterized to gain a deeper understanding of the structure formation and to identify interdependencies between process, formulation, and coating structure properties. The modification process and the formulation composition were varied to achieve a detailed conception of the relevant correlations. By relating the results to other structural properties, such as the theoretical porosity and thickness, it was possible to understand the formation of the coating structure in more detail.

(Invited) Additives in Cu Plating for Microelectronics Applications

Electrodeposition is a prevailing method in fabrication of Cu interconnects in microelectronics due to its ability to fill complex structures having a wide range of critical dimensions. A typical acidified Cu electrolyte contains a number of additives, organic and inorganic species in ppm amounts, with a specific role in the plating process. The additives in Cu plating have been extensively studied in the past couple of decades, and grouped according to their role in filling/creating features for microelectronics applications. This categorization is not a uniform one, and it might differ from author to author. In one popular convention, organic additives in the so-called three-component plating bath are named accelerator, suppressor and leveler, with their names hinting at how they influence Cu deposition. Ultimately, it is thanks to these additives that defect-free Cu features ranging from tens of nanometers to hundreds of micrometers can be economically fabricated. However, it is not enough to successfully fill a given single feature. The same has to be done for all the features on a 300 mm wafer, and then performed reproducibly over and over again. So, one needs to monitor the state of the electrolyte, i.e. of all the bath constituents, and either replace or replenish the electrolyte when the need arises. Additives could also have a strong influence on the physical properties of the deposit and therefore have a strong influence on the post-plating processing results. An additive that promotes void-free deposition of Cu structures in the end might not be used in a production line if it creates issues in the processing steps following electrodeposition. In our presentation we focus on a number of specific examples showing the effect of additives on nucleation and growth of Cu, propagation of Cu fronts on resistive substrates, post-plating processing, and their use in substrate surface modifications. A closer look is taken into in situ microscopic and electrochemical techniques and their use in studies of electrochemical nucleation and growth of Cu. We discuss advantages and drawbacks of potential step and galvanostatic deposition techniques in determining nucleation and growth parameters, and selection criteria for additive sets for a given plating task. We demonstrate that substrate surface modifications prior to plating could help simplify bath composition, i.e. eliminate need for some additives in the electrolyte, or improve the filling performance of the given plating bath. We also give examples of additives that promoted void-free filling of features but also influenced physical/mechanical properties of the final product in such a way that rendered it unusable in a specific application.

Effects of the hierarchical macro/mesoporous structure on the osteoblast-like cell response.

To improve the success of medical devices, implants with strong surface bioactivity are urgently required. Coatings with a macroporous structure produced by micro-arc oxidation possess advantages, such as strong adhesion to substrate and excellent resistance to wear and corrosion. Mesoporous structures contain pores with sizes of 2-50 nm, which can endow the biomaterials with the ability to enhance osteogenesis and to be loaded with diverse drugs. Thus, in this study, we aimed to evaluate the effects of both macroporous and mesoporous structures using a hierarchical macro/mesoporous structure to modify the titanium implant surface. The behaviors of SaOS-2 human osteosarcoma cells on the macro/mesoporous structure, including initial adhesion, proliferation, alkaline phosphatase (ALP) activity, and collagen secretion, were investigated. Cells that attached on the macro/mesoporous surface showed the highest cell numbers and greatest spreading area after incubation for 1, 2, and 4 h compared with the polished smooth substrate and macroporous surface in the presence of fetal bovine serum (FBS). However, in the absence of FBS, cell adhesion on the polished substrate, macroporous structure, and macro/mesoporous structure did not differ significantly. Cell proliferation on the macroporous and macro/mesoporous surfaces increased compared with that on the smooth substrate surface. Furthermore, ALP activity and collagen secretion were enhanced on the macro/mesoporous structure. Our findings provided important insights into the cellular responses to macro/mesoporous structures in the field of implant surface modification. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1896-1902, 2018.

High ${f}_{{T}}$ AlGa(In)N/GaN HEMTs Grown on Si With a Low Gate Leakage and a High ON/OFF Current Ratio

A 55-nm T-gate high-electron-mobility transistor was fabricated with a quaternary barrier AlGa(In)N/AlN/GaN heterostructure grown on a highly resistive Si substrate. The device shows a maximum current density of 1.25 A/mm, a peak extrinsic dc transconductance of 420 mS/mm, and the cutoff frequencies ${f}_{T}/{f}_{\text {max}}$ of 145/220 GHz, which gives a record high value of ( ${f}_{T}\cdot {f}_{\text {max}}{)}^{1/2} = 178$ GHz among the reported GaN-on-Si ratio frequency devices. The Al-rich quaternary barrier featured an incorporation of little indium, which yet significantly improved the crystalline quality, resulting in a record low gate leakage below 10−5 A/mm and a high ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio of $1.78\times 10^{5}$ .

Experimental Demonstration and Analysis of a 1.35-kV 0.92-m $\Omega \cdot \text {cm}^{2}$ SiC Superjunction Schottky Diode

This paper presents the fabrication, experimental analysis and electrical characterization of the first functional SiC superjunction (SJ) device. A trench-etching-and-sidewall-implant method has been developed to implement the SJ principle on a SiC Schottky diode. Several key process steps, including deep trench etching, ion implantation, and high-temperature annealing, are found to have noticeable influences on the device performances. The corresponding influences are studied by both simulation-aided theoretical analysis and experimental measurements. The highest measured cell blocking voltage was 1350 V, which achieves 95% of the simulated blocking voltage for the perfectly charge-balanced SJ structure. The measured device specific on-resistance was 0.92 $\text{m}\Omega \cdot \text {cm}^{2}$ . The SJ drift region specific on-resistance as low as 0.32 $\text{m}\Omega \cdot \text {cm}^{2}$ was obtained after subtracting the substrate resistance. This result successfully breaks the SiC 1-D unipolar limit.

Ex situ and in situ nanoscale wear mechanisms characterization of Zr/ZrxN tribological coatings

The lifetime of protective coatings is usually limited due to the formation of defects in the form of cracks, resulting in the destruction of coatings. Understanding the initial stages of structural defects during the wearing process of coatings on the nano- and atomic scale allows for predictions of the lifetimes of fabricated coatings.The main goal of the presented work was to study the nanoscale wear mechanisms of advanced Zr/ZrxN multilayer coatings both ex situ and in situ. These coatings allow for reduced failures due to crack deflection characteristics and the ability for layers by layer coating remove. The analysis indicated thatto increase the quality of the coating's adhesion, it was necessary to decrease the thickness of the metallic buffer layer. This decrease caused the formation of much finer, equiaxial grains, resulting in the stabilization of the isotropic residual stress of the total coating and the improved resistance to the formation of defects in the form of cracks. The adequate thickness of the buffer layer is a very important aspect in the explanation of the differences in the quality of coating adhesion; however, it is insufficient to explain differences in its wear resistance properties. The detailed microstructure study revealed that the nature of the tribofilm formed during the wear process might have a significant impact on the speed of its progression. The analysis showed that at higher phase ratios, namely, 1:4, with a larger amount of ceramic phase in the multilayer structure, a lower amount of the unfavourable hard tribofilm was produced.A similar behaviour was observed in the scratch experiments performed in situ of the scanning electron microscope. In the case of plastic dominated deformation, continuous chips were formed remaining within the scratch track. In the coating with ceramic dominated properties, the chips were discontinuous and moved away from the scratch track during the test. To have adequate coating adhesion to the substrate and appropriate wear resistance, it was necessary to limit the thickness of not only the first metallic buffer layer but also all the other metallic interlayers in the ceramic/metallic multilayer system. Limiting this thickness allowed for the stabilization of the residual stress at the substrate/coating interface and resistance to the formation of defects in the form of cracks, and it increased coating adhesion while minimizing the formation of unfavourable tribofilm, which accelerates the wear process.

On the Influence of the Photo-Induced Leakage Current in Monolithically Interconnected Modules

This paper describes the influence of an irradiance-dependent photo-induced leakage current through a semi-insulating GaAs substrate on the performance of photovoltaic monolithically series-interconnected multisegment laser power converters. A reciprocal relation between the resistivity of a semi-insulating GaAs substrate and irradiance of monochromatic light is experimentally observed. A reduced resistivity of the substrate with an increasing irradiation results in a substantial increase of a leakage current through the semi-insulating GaAs substrate between adjacent segments. For a multisegment laser power converter, this photo-induced leakage current is identified as a major shunting mechanism between adjacent segments that arises under high irradiances. Open-circuit voltage $V_{{\rm{oc}}}$ , fill factor (FF), and consequently conversion efficiency of a multisegment laser power converters are highly affected by the shunting mechanism. Based on a shading experiment, we observed that $V_{{\rm{oc}}}$ drops up to 21.5 mV per segment at a short-circuit current density $J_{{\rm{sc}}}= 47.3{\rm{\,A/ cm}}^{2}$ for the studied six-segment MIM specimen. For the same device, FF drops by 4.1% absolute at $J_{{\rm{sc}}}= 40.5{\rm{\,A/ cm}}^{2}$ . For the two-segment specimen, 5.8 mV drop of $V_{{\rm{oc}}}$ per segment and 1.5% absolute drop in FF is reported at $J_{{\rm{sc}}}= 47.3$ and $43.7{\rm{\,A/ cm}}^{2}$ , respectively.

Extremely large magnetoresistance in a high-quality WTe2 grown by flux method

We have grown single crystals of WTe2 by a self-flux method and evaluated the quality of the crystals. A Hall bar-type device was fabricated from an as-exfoliated film on a Si substrate and longitudinal resistance Rxx was measured. Rxx increased with an applied perpendicular magnetic field without saturation and an extremely large magnetoresistance as high as 376,059 % was observed at 8.27 T and 1.7 K.

RF MEMS Based Tunable Bandpass Filter For X-Band Applications

In this paper, we present the design and simulation of RF MEMS based Tunable combline band pass filters for X-band applications at different substrate thicknesses and studied the effect of thickness on tuning. The proposed filters are designed on high resistive silicon substrate of 500µm and 300 thicknesses. The tunability is achieved by using MEMS based varacter replaced with fix capacitor in conventional combline filter. First, the microstrip combline filter is designed at the centre frequency of 9.5 GHz and then tuning is achieved by varying the capacitance in the designed combline filters. The electromagnetic simulation has been carried out using HFSS v15 software based on finite element method (FEM). The tuning of the filter on silicon substrate of 500 μm is achieved by changing the capacitance value from 0.2035 pF to 0.4035 pF in the model in HFSS, which resulted the tuning in the frequency range of 7.85 to 10.35GHz. Insertion loss of design filter is in the range of 1dB within the tuning range. In case of substrate thickness 300 μm the tuning of the filter is achieved by changing the capacitance value from 0.293 pF to 0.403 pF in the model in HFSS, which resulted the tuning in the frequency range of 8.80 to 9.90 GHz. Insertion loss of design filter is in the range of ∼1.2dB within the tuning range.

Holocene resistant substrate and their roles in ecological safety of the Mu Us sandy land, Northern China

Resistant substrata are the sediments that are abundant in organic matter and outcropped as near-vertical cliff faces due to erosion. Palaeoenvironment research on resistant substrata (including lacustrine and peat sediments and palaeosols) is an important aspect of Quaternary science. Previous studies in the Mu Us sandy land in Northern China have focused on paleoclimatic evolution and aeolian activity, but the relationships between resistant substrata and modern human activity, and their role as animal habitats, are poorly understood. In this study, we used remote-sensing images and field investigations to produce a synthesis of the distribution of resistant substrata, and subsequently analyzed their roles in ecological safety. The results showed that they are closely related to the presence and economic activity of the local people who use them as sources of stable litter for animals, or for human dwelling places, and for agriculture. Our findings indicate that because of the value of eutrophic peat as a natural fertilizer and its function as a water-retaining layer, the location of modern agricultural zones is closely related to the distribution of ancient peatland. We also formulate a preliminary plan for the use of peatland for the development and extension of modern agriculture. In addition, we also consider its role as a protective layer preventing the reworking of the underlying sands and the potential risks if it is over-exploited. Our research is part of an attempt to focus attention on the relationships and potential applications of Quaternary research to environmental management and economic development of the region, emphasizing its utility for policy-makers and main stakeholders. Specifically, we anticipate that our study will provide a reference for subsequent efforts to balance economic development and resource conservation in this region.

D–T Neutron and 60Co-Gamma Irradiation Effects on HPSI 4H-SiC Photoconductors

The 14.1-MeV neutron irradiation- and 60Co-gamma irradiation-produced traps in high-purity semi-insulating (HPSI) 4H-SiC photoconductors (PCs) are reported, and the irradiation-induced changes in substrate resistivity, dark current, and UV response of the 4H-SiC PCs are analyzed. From the zero-bias thermally stimulated current measurements, six new traps at the energy levels $E_{v} \,+\, 0.58$ eV, $E_{v} \,+\, 0.68$ eV, $E_{v}\,+\, (0.7-0.9)$ eV, $E_{c} \, - \,0.64$ eV, $E_{c}\, -\, 0.91$ eV, and $E_{c} \, - \,1.04$ eV are identified in the 14.1-MeV neutron-irradiated PCs at the fluence of 1011 n/cm2, along the defects already detected before neutron irradiation. The thermal activation energy range (1–1.3 eV) for HPSI 4H-SiC is unaffected, and no considerable changes in the UV response of the PCs are noticed after the 14.1-MeV neutron irradiation. On the other hand, in addition to the traps determined prior to the irradiation, one new deep hole trap at $E_{v} + 1.31$ eV and significant changes in the activation energies (1.1–1.35 eV) are observed in the gamma-irradiated PCs at the dose of 100 Mrad, which suggest that the HPSI 4H-SiC substrate resistivity is increased due to the gamma irradiation-produced traps. Moreover, the signal-to-dark current ratio of the PCs is reduced after the gamma irradiation, as inferred from the UV response of the PCs.