Partial Schottky Research Articles

High‐Performance Self‐Powered Deep Ultraviolet Photodetector Based on NiO/β‐Ga2O3 Heterojunction with High Responsivity and Selectivity

A high‐performance self‐powered deep ultraviolet (DUV) photodetector based on the NiO/β‐Ga2O3 heterojunction is fabricated and analyzed. The NiO/β‐Ga2O3 heterojunction photodetectors are fabricated both with and without a post‐annealing process following NiO film deposition. Each photodetector structure is investigated through technology computer‐aided design simulations, including energy band diagram, trap density, and carrier concentration. The pristine self‐powered NiO/β‐Ga2O3 photodetector, lacking a post‐annealing process, exhibits partial Schottky contact formation between metal and NiO film, leading to performance degradation, including reduced responsivity, detectivity, and response time. On the other hand, the post‐annealed self‐powered NiO/β‐Ga2O3 photodetector demonstrates high performance such as a responsivity of 592.0 mA W−1, a detectivity of 4.30 × 1012 Jones, and response times of 30.93 ms and 72.32 ms, respectively. Therefore, the fabricated NiO/β‐Ga2O3 photodetector shows a promising potential for various applications requiring DUV detection without an external voltage bias.

Analysis of the Operation Mechanism of Superjunction in RC-IGBT and a Novel Snapback-Free Partial Schottky Collector Superjunction RC-IGBT.

This paper explores the operation mechanism of the superjunction structure in RC-IGBTs based on carrier distribution and analyzes the advantages and challenges associated with its application in RC-IGBTs for the first time. A Partial Schottky Collector Superjunction Reverse Conduction IGBT (PSC-SJ-RC-IGBT) is proposed to address these issues. The new structure eliminates the snapback phenomenon. Furthermore, by leveraging the unipolar conduction of the Schottky diode and its fast turn-off characteristics, the proposed device significantly reduces the turn-off power consumption and reverse recovery charge. With medium pillar doping concentration, the turn-off loss of the PSC-SJ-RC-IGBT decreases by 54.1% compared to conventional superjunction RC-IGBT, while the reverse recovery charge is reduced by 52.6%.

Injection enhanced SiC planar gate IGBT with partial Schottky contact emitter

A novel injection enhanced silicon carbide (SiC) planar gate insulated gate bipolar transistor with partial schottky contact emitter (PSE-IGBT) is proposed in this paper. The p-type schottky diode (p-SD) formed between the PSE and p-body region acts as a barrier to prevent the hole from flowing into the emitter, which enhances the conductivity modulation and optimizes the carrier distribution in the drift region in the conduction state. Therefore, compared with the conventional SiC IGBT (Con-IGBT), the device performance is significantly improved for the proposed structure. The simulation results show that the on-state voltage drop (Vceon) of the proposed SiC PSE-IGBT with the emitter metal of nickel (PSE-IGBTNi) and titanium (PSE-IGBTTi) is reduced from 6.61V of the SiC Con-IGBT to 5.83V and 5.48V, respectively. Meanwhile, the turn-off loss (Eoff) of the proposed SiC PSE-IGBTNi and PSE-IGBTTi is only 11.15 mJ/cm2 and 9.80 mJ/cm2, which is 47.5% and 53.9% lower than 21.25 mJ/cm2 of the SiC Con-IGBT at the Vceon of 6.4V, respectively. Furthermore, turn-off capability at high temperature and large current is checked and no degradation of the turn-off capability is observed for the proposed SiC PSE-IGBTs.

Novel non-stoichiometric (Ba0.91Ca0.09)x(Zr0.18Ti0.82)O3 ferroelectric ceramics with improved diffuse phase transition and dielectric tunable performance

Dielectric tunable properties in ferroelectric ceramics have been optimized by a variety of approaches, e.g., isovalent/aliovalent substitution, system composite et al., while the study of non-stoichiometric regulation on the performance of BCZT ceramics was rarely concerned. Herein, a series of novel non-stoichiometric (Ba0·91Ca0.09)x (Zr0·18Ti0.82)O3 (BCZTx) ceramic specimens were successfully prepared via solid-state reaction. The microstructures of BCZTx ceramics are simultaneously investigated through XRD and SEM. The diffuse phase transition (DPT) behaviour of BCZTx ceramics are studied by the Lorentz-type empirical formula. The significant enhancement of DPT behaviour is observed at x = 1.03, which probably due to the coaction of the generation of partial Schottky defects and prominent reduction of grain size. Furthermore, a high tunability (k) 87.80%, low dielectric loss (tan δ) 0.141%, and a remarkably enhanced FOM of 623 are achieved in x = 0.99 at a low DC bias electric fields (BEFs) of 7.28 kV/cm and room temperature (RT), which is superior to that of the stoichiometric BCZT ceramics and other available reported BT-based ceramics systems in term of the dielectric tunable properties. Meanwhile, it shows that the temperature dependent CQF value of x = 0.99 remained advantageous around the RT. These findings suggested that non-stoichiometric BCZTx ceramics with x = 0.99 are significantly competitive in the applications of dielectric tunable devices at RT. The non-stoichiometric regulation is an effective approach in improving the dielectric tunability properties of BCZT ceramics.

Effects of non-stoichiometric defects on the dielectric properties of (Ba0.5Sr0.5)xTiO3-ZnGa2O4 composite ceramics

In order to explore the effects of non-stoichiometric defects on the dielectric properties of composite ceramics, 70 wt% (Ba0.5Sr0.5)xTiO3-30 wt%ZnGa2O4 ((BS)xT50-ZG, x = (Ba + Sr)/Ti = 0.99, 1.00, 1.01 and 1.05) composite ceramics were fabricated by the traditional sintering technique. The association between structure and dielectric properties has been studied. The results show that the distortion of the crystal lattice brought by the partial Schottky defects, namely [V″Ba,Sr–V˙˙O]× and [V′′′′Ti–2V˙˙O]×, induces a decrease in the Curie temperature of (BS)xT50-ZG composite ceramics. The orientation of the elastic dipoles brought by oxygen vacancies causes the pinning of the domain walls, which reduces the dielectric loss at low frequencies. Tunability is related to the dipole polarization caused by [V″Ba,Sr–V˙˙O]× and [V′′′′Ti–2V˙˙O]× defect complexes. In addition, compared with the composite ceramic with x = 1, the Q values of the composite ceramics with x < 1 and x > 1 decreases due to the deterioration of the microstructure homogeneity and the enhancement of the disorder of the B-site cations in (BS)xT50.

Investigation of 4H-SiC Extraction-Enhanced Vertical Insulated-Gate Bipolar Transistor with Lightly Doped Extractor in Collector Region

This paper proposes a new N-type 4H-SiC extraction-enhanced vertical insulated-gate bipolar transistor (E2VIGBT), which uses a partial Schottky contact to the collector region bottom surface as a carrier extractor to enhance the carrier extraction, so that the switching performance will be improved. TCAD simulation shows that, at an operation frequency of 250 kHz, the E2VIGBT offers a turn-off loss decrease of 69.2% and a total energy loss in a single period reduction of 34.4% when compared with conventional field-stop 4H-SiC IGBTs. With further specific optimization, the proposed structure consumes less energy in a much wider frequency range. The simulation results indicate that this new type of IGBT performs better in high frequency applications.

Structures and energetics of point defects with charge states in zircon: A first-principles study

The fundamental problem of point defects under different phase equilibrium conditions in zircon (ZrSiO4) is carried out by first-principles calculation. The formation energies with the structural deformation of various native defects, i.e., single vacancy, interstitial, Frenkel and Schottky pairs at different charge states are calculated, which agree well with the available results. We identify VO2+ shows an important role in non-stoichiometric regime of ZrSiO4−x (x < 1). When Fermi level (εF) locates close to the CBM, the VZr4− becomes more easily observed than VO2+ in O-rich environment. In turn, the most abundant interstitial defects are IZr4+ and ISi4+. The non-interacting Si Frenkel-pair, made of the association of quadruply charged defect in energy of 5.947 eV, is more likely to form than other type of Frenkel-pairs. By formation the complex defects associating partial and full Schottky defects requires higher formation energy. These results provide a good reference to understand storage state as well as disposal of excess weapons-grade Pu and high-actinide wastes.

Density Functional Theory Modeling of Cation Diffusion in Bulk Lanthanum Manganite and Tetragonal Zirconia for Solid Oxide Fuel Cell Applications

Cation diffusion in perovskites such as La1-xSrxMnO3±δ (LSM) and fluorites such as Yttria Stabilized Zirconia (YSZ) plays a key role in controlling performance and long-term stability of solid oxide fuel cells (SOFCs) and of the corresponding electrode/electrolyte interfaces. For point defects based cation migration mechanisms, discrepancies between experimental studies and atomistic modeling results are generally observed when trying to identify the apparent activation energies of the cation diffusivities. In particular, computational modeling of the simple point defect migration generally overestimates the apparent activation energies by several eVs [1-3] relative to experimental results. Despite the existence of few proposed defect cluster pathways in the SOFC literature, the corresponding energetics based on atomistic level modeling is quite limited. As a result, outstanding questions related to the influence of the local bonding environment of the material upon the activation energies of cation diffusion and upon the energetics of the defect cluster carriers are still open. In this presentation, density functional theory (DFT) calculations of the cation diffusion involving mechanisms beyond the isolated point defect migration mechanism are discussed in connection to SOFC applications. The barriers of the cations, cation vacancy clusters, and cation impurities migration as well as their corresponding saddle point configurations in bulk LaMnO3±δ (LMO) and tetragonal ZrO2 are investigated. For cation vacancy migration in both LaMnO3 and tetragonal ZrO2 systems, it was revealed that significant reduction in the barriers of 1~3 eV takes place when there exists an additional nearest neighbor vacancy or a nearest neighbor vacancy pair bound to the original cation vacancy transport carrier (i.e., partially or fully bound Schottky defects). Such a significant reduction in the migration barriers of isolated cation vacancy migration due to the presence of an additional nearest neighbor vacancy or a vacancy pair invokes the need to examine other possible defect cluster diffusion mechanisms that exhibit attractive or weakly repulsive interactions between point defects. For example, our recent studies [1,3] suggest that the presence of a nearest neighbor B-site cation vacancy in bulk LMO decreases the electrostatic repulsion and steric constraints to the migrating A-site cations in the transition state configurations, leading to a more active A-site cation diffusion with apparent activation energies in good agreement with the experimental measurements. An analogous scenario is also observed for the Lanthanide impurity migration (via a cation vacancy related mechanism) in tetragonal ZrO2, where the migration barriers of partial and full Schottky bound defects are about 1.5 and 2.4 eV lower than those of simple cation vacancy migration (about 3 eV). By considering the attractive interactions of -1.0 and -1.4 eV for the partial (VZr-VO) and full (VO-VZr-VO) bound Schottky defects along with the separated Schottky defect formation energies of 4~5 eV (in a 288-atom ZrO2 supercells), it follows that cation impurity diffusion via partially and fully bonded Schottky defects could be more active than the cation vacancy migration of the separated Schottky defects in tetragonal ZrO2. Finally, the trends in the migration barriers of the defect cluster mechanisms among several types of cation impurities relevant for SOFC applications in LMO and tetragonal ZrO2 will be also discussed.

Critical Role of Water in Defect Aggregation and Chemical Degradation of Perovskite Solar Cells.

The chemical stability of methylammonium lead iodide (MAPbI3) under humid conditions remains the primary challenge facing halide perovskite solar cells. We investigate defect processes in the water-intercalated iodide perovskite (MAPbI3_H2O) and monohydrated phase (MAPbI3·H2O) within a first-principles thermodynamic framework. We consider the formation energies of isolated and aggregated vacancy defects with different charge states under I-rich and I-poor conditions. It is found that a PbI2 (partial Schottky) vacancy complex can be formed readily, while the MAI vacancy complex is difficult to form in the hydrous compounds. Vacancies in the hydrous phases create deep charge transition levels, indicating the degradation of the lead halide perovskite upon exposure to moisture. Electronic structure analysis supports a mechanism of water-mediated vacancy pair formation.

Evaluation of thermodynamics, formation energetics and electronic properties of vacancy defects in CaZrO3

Using first-principles total energy calculations we have evaluated the thermodynamics and the electronic properties of intrinsic vacancy defects in orthorhombic CaZrO3. Charge density calculations and the atoms-in-molecules concept are used to elucidate the changes in electronic properties of CaZrO3 upon the introduction of vacancy defects. We explore the chemical stability and defect formation energies of charge-neutral as well as of charged intrinsic vacancies under various synthesis conditions and also present full and partial Schottky reaction energies. The calculated electronic properties indicate that hole-doped state can be achieved in charge neutral Ca vacancy containing CaZrO3 under oxidation condition, while reduction condition allows to control the electrical conductivity of CaZrO3 depending on the charge state and concentration of oxygen vacancies. The clustering of neutral oxygen vacancies in CaZrO3 is examined as well. This provides useful information for tailoring the electronic properties of this material. We show that intentional incorporation of various forms of intrinsic vacancy defects in CaZrO3 allows to considerably modify its electronic properties, making this material suitable for a wide range of applications.

Dielectric properties and vacancy‐like defects in plasma‐sprayed barium titanate

AbstractPositron annihilation spectroscopy was employed for investigation of vacancy‐like defects in plasma‐sprayed barium titanate. Defect studies were combined with measurement of dielectric properties of barium titanate coatings. Samples prepared by gas‐stabilized plasma spray (GSP) torch and by plasma torch with the hybrid water‐argon stabilization (WSP‐H) were studied. Processing parameters were selected so that GSP coatings were sprayed in reductive conditions, whereas WSP‐H coatings were prepared in oxidizing environment. As‐sprayed GSP coating is dark, whereas WSP‐H one is light. The dielectric properties of WSP‐H coating are superior to those for GSP one. Defect studies revealed that both GSP and WSP‐H coatings contain titanium vacancies. However, GSP coating contains in addition a considerable concentration of oxygen vacancies. Some fraction of oxygen vacancies in GSP coating is coupled with titanium vacancies forming partial Schottky defect. The structure of WSP‐H coating is less disordered and contains only a low concentration of oxygen vacancies. This is consistent with reductive and oxidizing conditions in GSP and WSP‐H spraying, respectively. Annealing at elevated temperatures in air leads to removal of oxygen vacancies which are filled by oxygen diffusing into the samples.

Effect of the (Ba + Sr)/Ti ratio on the microwave‐tunable properties of Ba0.6Sr0.4TiO3 ceramics

AbstractThe impact of the (Ba + Sr)/Ti (A/B) ratio on the microwave‐tunable characteristics of diffuse phase transition (DPT) ferroelectric Ba0.6Sr0.4TiO3 (0.6‐BST) ceramics was investigated. The reduction in the lattice constant with increasing nonstoichiometry was attributed to introduced partial Schottky defects, i.e., and . The magnitude of the dielectric constant, ε′, at room temperature in the absence of an applied electric field was governed by the shift in the dielectric maximum temperature, Tm, because Tm was close to room temperature for the 0.6‐BST. The dielectric loss, tanδ, diminished as the ε′ decreased for 0.98≤A/B≤1.05, while the tanδ was much higher for A/B=0.95 having the greatest A‐site vacancy loading. The negatively charged and were mainly compensated by oxygen vacancies and likely partly compensated by holes, h•, which contributed to the electrical conduction. The tunability, T, at 100 MHz was almost constant at 20%–25% for A/B≥1.00 despite the reduction of the ε′, whereas T decreased for A/B&lt;1.00 to ca. 10% for A/B=0.95 having the greatest A‐site vacancy loading. The results implied that the for larger A/B values was more efficient in generating nucleation sites in the polar nanoregions (PNRs) than the for smaller A/B values, thereby providing greater dipole polarization. Consequently, the figure of merit, FOM, reached its maximum of 250 at A/B=0.9875, which was ca. 155% higher than that of the stoichiometric BST.

First-principles investigation of vacancies in LiTaO3

Formation energies of neutral and charged vacancies in lithium tantalate, as well as their electronic states have been investigated through first-principles calculations. It is found out that , and are the most energy favorable vacancies on O, Li and Ta sites respectively. The formation energy of vacancy on the O site is lower in oxygen poor environments than that in oxygen rich environments, and the formation energy of vacancy on the cation site is lower in oxygen rich environments than that in oxygen poor environments. Among all types of neutral vacancies considered in this study, the energy of Li partial Schottky reaction, 2 + , is the lowest at almost all considered chemical environments. Taking into account the distribution of vacancy induced energy levels, we suggest that either or is responsible for the light absorption band around 460 nm observed in annealed LiTaO3 crystal.

First-principles characterization of chemical stability, defect formation energies and n-type conductivity in SrZrO3

Thermodynamics and the electronic structure of intrinsic vacancies in SrZrO3 have been investigated by using density functional theory based ab-initio calculations. Our results indicate that the hole-doped state can be achieved in Sr and Zr deficient SrZrO3, while the O vacancy retains the insulating character by introducing a defect level in the band gap. We utilize electronic charge density calculations and atoms-in-molecules concept to elucidate the changes in electronic properties by introducing the vacancy defects. The variation of formation energy as a function of Fermi level shows that fully charged oxygen vacancy in SrZrO3 can lead to a hole-doped state. Moreover, we explore the chemical stability and defect formation energies of charge neutral and fully charged intrinsic vacancies under various synthesis conditions and analyze full and partial Schottky reactions. In addition to intrinsic vacancy defect, the clustering of neutral oxygen vacancies in SrZrO3 is examined in different crystallographic planes which provides useful information for tailoring the electrical conduction of this material. Therefore, we propose that hole-doped, semiconducting and n-type character in SrZrO3 further enhance its device application for semiconductor industry which are achievable through intentional incorporation of intrinsic defects and oxygen vacancy clustering.

First-principles study of thermodynamic stability and the electronic properties of intrinsic vacancy defects in barium hafnate

The formation of intrinsic vacancy defects in barium hafnate, BaHfO3 and their corresponding electronic structures have been investigated using first-principles calculations. The thermodynamics of pristine and vacancy defects containing barium hafnate have been analyzed. Formation energies for neutral and fully charged Ba, Hf and O vacancies have been evaluated for determining their stability with respect to different chemical environments. From the calculated electronic structure and density of states, it is found that cation deficient barium hafnate is hole-doped, while the incorporation of oxygen vacancy retains the insulating nature of this material. The defect reaction energies for partial and full Schottky reactions are also computed, which controls the properties of non-stoichiometric barium hafnate.

Thermodynamic Stability and Vacancy Defect Formation Energies in SrHfO3

Density functional theory based ab initio calculations are used to investigate the thermodynamic stability, defect formation energies, and electronic properties of isolated neutral and charged vacancies in SrHfO3 under various chemical environments. We find that cation defects lead the system into a hole-doped state, while oxygen vacancies yield defect levels near the conduction band minimum. The partial and full Schottky defect reaction energies and mixed electron hole conduction behavior of SrHfO3 is also evaluated. Furthermore, various cases for neutral oxygen vacancy clustering are examined for tuning the electrical properties of oxygen deficient SrHfO3. We show that ordered oxygen vacancies in HfO layers are energetically favorable and induce metallicity in this system which emerges due to charge transfer between the vacancy site and the hafnium dangling bond.

Chemical stability and defect formation in CaHfO3

Defects in CaHfO3 are investigated by ab initio calculations based on density functional theory. Pristine and anion-deficient CaHfO3 are found to be insulating, whereas cation-deficient CaHfO3 is hole-doped. The formation energies of neutral and charged cation and anion vacancies are evaluated to determine the stability in different chemical environments. Moreover, the energies of the partial and full Schottky defect reactions are computed. We show that clustering of anion vacancies in the HfO layers is energetically favorable for sufficiently high defect concentrations and results in metallicity.

Defect energetics in LaAlO3polymorphs: A first-principles study

Formation energies of intrinsic defects in rhombohedral and cubic LaAlO${}_{3}$ were calculated using a first-principles projector augmented wave method based on the density functional theory. Defect energetics of single-atom vacancies, partial and full Schottky defects, and antisite cationic defects were investigated. Finite-size cell interactions in charged defects were corrected by calculating with various supercell sizes up to 480 atoms, and band-gap correction was also performed for neutral oxygen vacancy. It was found that the defect formation behaviors of both rhombohedral and cubic LaAlO${}_{3}$ are very similar to each other, that is, Schottky-type defects are preferably formed under all atmospheres and that the formation of neutral oxygen vacancies requires much more energy compared with other perovskite oxides.

The Structure and Defect Formation Energy in Tetragonal PbTiO3: Ab Initio Calculation

The first-principles calculation had been adopted to investigate the intrinsic vacancies in bulk PbTiO3. The atomic relaxation and the formation energy of isolated neutral vacancy were studied respectively. And the defect reaction energies of Pb partial Schottky (VPb 2−+VO 2+), Ti partial Schottky (VTi 4−+2VO 2+), and full Schottky (VPb 2−+ VTi 4−+3VO 2+), were obtained. It was found that both the formation energy of vacancy and the defect reaction energy were connected closely with the thermodynamic condition. By comparing the calculated formation energy values, Pb partial Schottky (VPb 2−+VO 2+) was considered to be the dominant defect species in the seven thermodynamic conditions, consistent with the experimental reports.

First-principles study of defect properties in tetragonal BaTiO3

Based on density functional first principles method, the defect properties in tetragonal BaTiO 3 have been studied. The results showed that the formation energies of neutral Ti vacancy and partial Schottky defect 2 V 3- Ti +3V 2+ O are the lowest under oxygen-rich condition; while under reducing condition oxygen vacancy becomes the primary defect. The calculated full Schottky formation energy is higher than that obtained in the cubic phase, which may be the result of the strong hybridization between the Ti-O bonds. The hybridization is also responsible for the Frenkel formation energy of Ti. The defect-interactions are important when dealing with Schottky defects.