Bandgap Narrowing Effect Research Articles

Facile Synthesis of Bandgap-Engineered N-Doped MgO/g-C3N4 Nanocomposites for Enhanced Sunlight-Driven Photocatalytic Degradation of Organic Dyes

This study tests the theory of using a p-n junction to inhibit the recombination of photo-generated electrons and holes in N-MgO/g-C3N4 for the photocatalytic degradation of methylene blue (MB) dye. While the use of n-type semiconductor junctions with g-C3N4 for bandgap narrowing is well-studied in dye degradation, this research explores the innovative application of nitrogen (N)-doped MgO to create a p-type junction with n-type g-C3N4. The N-MgO/g-C3N4 nanocomposites were designed and synthesized to leverage both the bandgap narrowing effect and the formation of a p-n junction. The results demonstrate that these nanocomposites can effectively degrade MB dye under sunlight, achieving over 90% degradation efficiency with a bandgap of 2.63 eV. Under high pH conditions, the degradation efficiency further increased to 94%. The enhanced photocatalytic activity of the N-MgO/g-C3N4 composite is attributed to the formation of a heterojunction, which facilitates efficient separation and transmission of photo-induced charge carriers. This study discusses the detailed mechanism of this enhanced activity, emphasizing the role of the p-n junction in promoting effective charge separation and transfer, thereby improving the photocatalytic performance under sunlight.

Effective bandgap narrowing and enhanced optoelectronic performance of Cs2PtBr6 double perovskites by pressure engineering.

Tuning the structure-property relations of perovskites by pressure engineering holds great promise for discovering materials with favorable properties. The newly synthesized Cs2PtBr6 double perovskite exhibits excellent water resistance and chemical stability. Yet its photoelectric conversion efficiency is limited by its intrinsic wide-bandgap nature. In this work, based on density functional theory calculations, we demonstrate the bandgap narrowing of Cs2PtBr6 via pressure engineering and maintain its structural stability. Strikingly, upon applying pressure up to 12 GPa, the bandgap value decreases to 1.34 eV, which exactly reaches the optimal bandgap required by the Shockley-Queisser efficiency limit. Moreover, optical calculation analysis shows that the optical absorption of Cs2PtBr6 exhibits a significant improvement within the visible range. Therefore, the potential of Cs2PtBr6 as a photovoltaic material by pressure engineering is improved. This work is useful for designing and synthesizing new perovskite materials with enhanced performance.

Physical mechanism of Zn and Te doping process of In0.145Ga0.855As0.108Sb0.892 quaternary alloys

We investigated p- and n-type In0.145Ga0.855As0.108Sb0.892 semiconductor alloys grown on GaSb (100) substrates by the liquid phase epitaxy (LPE) technique with different Zinc (Zn) and Tellerium (Te) mole fractions, respectively. Photoluminescence (PL) spectra showed a band gap narrowing effect for p-type doping and a band gap widening for n-type doping, attributed to the type of carrier concentration. The carrier concentration was determined from the band-to-band transition of the PL spectra in the range of 1.20 × 1016 to 2.80 × 1017 and 7.75 × 1016 to 1.02 × 1018 cm−3 for electrons and holes, respectively. Raman spectroscopy measurements showed the phonon modes LO (GaSb–InAs)-like and TO (GaSb–InAs)-like for both types of doping. The frequency dispersion of these modes is closely tied to the presence of native defects, such as vacancies of Ga(VGa), antisites of Ga in Sb (GaSb), and VGa–GaSb complexes. Incorporation of Zn- and Te-doping into the lattice led to a notable reduction in the full width at half maximum (FWHM) of the LO (GaSb–InAs)-like mode, as these dopants effectively diminished native defects. A detailed model is presented for the incorporation of dopants and their effect on the crystal quality. Phonon–plasmon coupling was observed through the L− mode, which overlaps with the TO (GaSb–InAs)-like mode for the carrier concentrations observed in the doped alloys. A theoretical estimation of the frequencies of the coupled modes L+ and L− was implemented as a function of the carrier concentration, based on the effective dielectric function of the quaternary compound. The L+ coupled mode shifts from the phononic to the plasmonic domain for theoretical electron concentrations ranging from ∼1017 to 5 × 1018 cm−3, while in p-type conductivity, the L+ mode remains in the phononic domain for the same range of hole concentrations. The increase in the frequency of the L+ mode with carrier concentration, such as the plasma frequency, provides another reliable method for determining carrier concentrations. This study reveals the physical mechanism of Zn an Te incorporation into InGaAsSb, which is required for the integration of p- and n-type doped quaternary alloys into optoelectronic applications. In addition, it provides a comprehensive understanding of the complex interaction mechanisms, including LO phonon–plasmon coupling modes and optical transitions, opening up new lines for exploring the electrical and structural properties of these materials.

S-Doped Hollow Multi-Metallic Prussian Blue Analogue (PBA) Nanoplatform for Enhanced Anticancer for Cervical Cancer.

Developing novel multimodal nanomaterials-based anticancer agents to meet complex clinical demands is an urgent challenge. This study presents a novel uniform hollow S-doped NiCuFe Prussian blue analogue (NiCuFe-S) with satisfactory size and properties as anticancer agents for efficient cervical cancer therapy using a simple and environmentally friendly procedure. The formation mechanism and the reason for enhanced performance of NiCuFe-S were characterized and discussed by diverse spectroscopic and microscopic methods. Moreover, to demonstrate the anti-cancer ability of NiCuFe-S, in vitro and in vivo experiments were carried out. Compared to the non-doped NiCuFe, the NiCuFe-S exhibited significantly enhanced photothermal and catalytic activity attributed to the electronic bandgap-narrowing effect and the increased electron circuit paths resulting from S doping. The hollow structure of NiCuFe-S facilitated the loading of small-molecule drugs, such as doxorubicin (DOX), transforming it into a multimodal nanoplatform for cervical cancer treatment. In vitro and in vivo experiments proved the potential of the NiCuFe-S nanotheranostic agent for chemodynamic therapy (CDT), photothermal therapy (PTT), and chemotherapy for cervical cancer. This research not only overcomes inherent limitations but also significantly broadens the applications of Prussian blue analogues in biomedicine.

Investigations of microstructures and thermoelectric properties of TiNiSn half-Heusler compounds with micro- and nano-scale copper additions

The TiNiSn-based half-Heusler compounds have been considered as a promising thermoelectric material system for waste heat recovery applications. There have been numerous studies dedicated to improving its intrinsic low thermoelectric performance, and one strategy is to incorporate certain types of metal dopants into the host materials. Only a few research works have been focused on the effects of the dimensions of metal particles on the thermoelectric properties of materials. In this study, we investigate the roles of micro- (M) and nano-scale (N) Cu powders in affecting the microstructures and thermoelectric properties of TiNiCuxSn (x = 0−0.1) compounds. Owing to the ease of oxidation of Cu nanoparticles and the tedious preparation procedure, TiNiCux, NSn shows lower carrier concentration and electrical conductivity compared to the TiNiCux, MSn with the same nominal Cu content. The high-temperature Seebeck coefficient of TiNiCux, NSn gradually deteriorates as the temperature rises, partly due to the impurities-induced bandgap narrowing effect. The maximum power factor achieved for TiNiCux, NSn is about 20.2% lower than that for TiNiCux, MSn. Even though the reduced contribution of electronic component leads to a lower total thermal conductivity at low temperatures, the highest zT obtained in TiNiCux, NSn is markedly lower than that in the corresponding TiNiCux, MSn. These findings highlight the importance of investigating the dimensions of metal dopants in studies of the thermoelectric properties of materials.

Correlated carrier transport and optical phenomena in CdO layers grown by plasma-assisted molecular beam epitaxy technique

In this work, we have investigated a series of CdO layers grown by the plasma-assisted molecular beam epitaxy technique on the m-plane sapphire substrate. The relation between Cd and O2 parameters during growth influences the stoichiometry of the CdO layers and it affects morphological, optical, and electrical properties which are manifested in the roughness parameter, lattice constant, optical bandgap, and electrical parameter of the layers. The surface morphology and structural properties of CdO layers were studied using atomic force microscopy and X-ray diffraction respectively. Temperature-dependent Hall measurement revealed the maximum mobility of 352 cm2V−1s−1 achieved at room temperature with a carrier concentration of about 4.5 × 1019 cm−3. The optical properties and bandgap of CdO layers were investigated using UV–Visible spectroscopy at room temperature. It is observed that the shift of the bandgap depends upon the carrier concentration and is acquired by combining the effect of bandgap widening and bandgap narrowing.

Oxygen vacancy luminescence and band gap narrowing driven by Ce ion doping with variable valence in SnO2 nanocrystals

Although considerable research works have witnessed the important modulations of oxygen vacancies on the optical, electrical, and magnetic properties of SnO2 nanostructures, it is not easy to control oxygen vacancy defects in such systems.The difficulty stems from that oxygen vacancy is a kind of atomic defect, and its distribution is sensitive to process conditions and external factors, which makes direct characterization and purposeful control difficult. The purpose of this work on Ce-doped SnO2 nanocrystals is to investigate the tolerance of the host lattice to Ce ions, the population and evolution of Ce3+/Ce4+ ions, and the possibility to adjust oxygen vacancies by Ce3+ ions, and then focus on the influence of oxygen vacancy defects on the band gap and luminescence performance. As Ce doping concentration increases from 0 to 12 at.%, the doped system changes from Ce3+ dominated at low doping amount (≤3 at.%) to Ce3+/Ce4+ coexistence at medium doping concentration (3 at.% ∼ 9 at.%), to occurrence of CeO2 impurity phase at over doping (∼12 at.%). The optimum doping occurs at 6 at.%, which corresponds to the saturated critical point of Ce3+ content and the maximum oxygen vacancy concentration. Importantly, the oxygen vacancies in the current Ce-doped SnO2 nanocrystals is directly regulated by the Ce3+ ion concentration on the Sn sites, which plays an important role in the band gap tuning and visible light emission. With Ce concentration increasing from 0 to 12 at.%, the band gap monotonicity decreases from 3.36 eV to 3.12 eV, while the intensity of the oxygen vacancy luminescence band first increases and then decreases, with the turning point at 6 at.%. Both band gap narrowing effect and enhanced emission indicate that Ce-doped SnO2 should be a promising method to design and manufacture visible light responsive SnO2 based optoelectronic materials by manipulating oxygen vacancy defects.

Chromium-doped ZnO nanoparticles synthesized via auto-combustion: Evaluation of concentration-dependent structural, band gap-narrowing effect, luminescence properties and photocatalytic activity

Herein we report the effect of the Cr3+ content on the distinctive features of the first-ever auto-combustion-synthesis-produced Cr3+ doped ZnO nanoparticles utilizing leucine as the fuel. To assess the impact of fuel and Cr3+ content on the structural, optical, and luminescence characteristics, as-synthesized powders were systematically examined using powder XRD, UV–Visible, and Photoluminescence spectroscopy. Structural studies show that the exothermicity of the redox mixture containing oxidizer and fuel combination leads to the development of polycrystalline, single-phase, and nanosized particles. XRD analysis shows that, reduced crystallite size with Cr3+ content. In contrast, other characteristics like lattice parameters, unit cell volume, strain, and dislocation density, were shown to increase linearly with Cr3+ concentration up to 7 mol%. Additionally, it is seen that the predicted Urbach energy values rise as Cr3+ is added to the ZnO host matrix, indicating that the substitution of Cr3+ for Zn in the host ZnO lattice has increased structural disorder. In contrast to the other samples, the 5 mol% Cr3+ doped ZnO sample exhibits the emission near the white region according to the PL emission measurements. Furthermore, the photocatalytic activity of the as-prepared Cr3+ doped ZnO NPs was examined. It was found that the as-prepared samples exhibit outstanding photocatalytic activity in the visible wavelength region against Malachite Green (MG) dye. Among all, 9 mol% Cr3+ doped ZnO has shown the maximum 95.4% degradation against MG dye. All the investigated results conclude that the produced Cr3+ doped ZnO nanoparticles could be exploited in a variety of upcoming optoelectronic and photocatalytic applications.

Improved photocatalytic, antimicrobial and photoelectrochemical properties of nanocrystalline Cu2+-doped ZnO nanoparticles

Herein we present the first report on the synthesis of Cu2+-doped ZnO nanoparticles via the solution-combustion using a new fuel (Glutamine). Systematic studies were carried out to assess the influence of Cu2+-concentration on photocatalytic, antimicrobial, and photoelectrochemical characteristics through various characterizations such as XRD, SEM-EDS, FTIR, UV–Visible, photocatalytic, antimicrobial, photoelectrochemical and Photoluminescence. XRD results show the formation of single-phase nanocrystalline particles and the substitution of Cu2+ at the Zn2+ site without the occurrence of impurity phases. SEM & EDS analysis revealed almost spherical particles and nominal (measured and experimental) element compositions. The structural changes induced due to the substitution of Cu2+ into the ZnO host lattice are evident in FTIR data, which show the presence of stretched ZnO bonds. The band gap narrowing effect was observed up to 5 mol% Cu2+ and thereafter band gap widens. PL spectra exhibit multiple emission peaks related to defects present in the host ZnO induced by the Cu2+ & PL intensity increases with the increase of doping concentration up to 3 mol % of Cu2+ beyond that its decreases with increasing concentration. The prepared NPs demonstrate promising photocatalytic activity against MB dye in both the UV and visible ranges. The maximum 94% percentage degradation was recorded for 9 mol% CuZnO, which is the highest among CuZnO NPs reported to date. In addition, 3 mol% and 2 mol% CuZnO NPs have shown potential antimicrobial activity against Bacillus and Pseudomonas respectively. The possible mechanism for both photocatalytic activity and antimicrobial activity is demonstrated. Furthermore, 5 mol% CuZnO has shown the largest transient photocurrent of 1.147 mA/cm2, which is ∼12 times larger than undoped ZnO (0.096 mA/cm2) due to the band-gap narrowing, suggests the possibility of photoelectrochemical sensors.

Photoluminescence characterization of GeSn prepared by rapid melting growth method

In this work, single crystalline GeSn on insulator (GSOI) were grown by rapid melting growth (RMG). The Sn content distribution along the strip was investigated, reaching to 7.8% near the end of the strip. The GeSn strip had high quality with no threading dislocations, as revealed by cross-sectional transmission electron microscopy (XTEM). Photoluminescence (PL) measurements along the strip were performed to check the indirect-direct bandgap transition Sn content of GeSn alloys. It was found the integrated PL intensity increased about 6.6 times for Sn content 0.86%–7.8%. For GeSn with Sn content 6.1%, the temperature-dependent PL shows that the energy difference between direct Γ-Γ valley and indirect L-Γ valley decreases due to the bandgap narrowing (BGN) effect, and the direct band transition gradually dominates the PL spectra as temperature increases. The temperature-dependent PL spectra have only one peak for GeSn with Sn content 7.8%, suggesting the direct bandgap property. These results indicate that GeSn grown by RMG is very promising for fabricating efficient Si based light sources.

Effect of cobalt incorporation on the photocatalytic degradation of brilliant green using SnO2 nanoparticles under visible light irradiation

• Bare and Co-doped nanocrystals of SnO 2 were synthesized by a simple chemical precipitation method. • The result of UV-DRS proposed a band gap narrowing effect on SnO 2 with cobalt doping. • The defects and vacancies induced band gap reduction and increased BET surface area on cobalt doping, have played a vital role in the photochemistry of SnO 2 . Suggested here are a simple chemical precipitation method in order to synthesize bare and various levels of Co doping samples. The harvested samples were tested for their structural, optical, morphological and photocatalytic properties. The optical study shows a decline in the band gap of SnO 2 on 0.075 M of cobalt doping. The tuned band gap of SnO 2 on doping utilizes the visible light for the photodegradation of brilliant green (BG) and recommends the usage of the optimum level of Co-doped SnO 2 in environmental remediation applications.

Performance Investigation of a Proposed Flipped npn Microstructure Silicon Solar Cell Using TCAD Simulation

This work aims at inspecting the device operation and performance of a novel flipped npn microstructure solar cell based on low-cost heavily doped silicon wafers. The flipped structure was designed to eliminate the shadowing effect as applied in the conventional silicon-based interdigitated back-contact cell (IBC). Due to the disappearance of the shadowing impact, the optical performance and short-circuit current density of the structure have been improved. Accordingly, the cell power conversion efficiency (PCE) has been improved in comparison to the conventional npn solar cell microstructure. A detailed analysis of the flipped npn structure was carried out in which we performed TCAD simulations for the electrical and optical performance of the flipped cell. Additionally, a comparison between the presented flipped microstructure and the conventional npn solar cell was accomplished. The PCE of the conventional npn structure was found to be 14.5%, while it was about 15% for the flipped structure when using the same cell physical parameters. Furthermore, the surface recombination velocity and base bulk lifetime, which are the most important recombination parameters, were studied to investigate their influence on the flipped microstructure performance. An efficiency of up to 16% could be reached when some design parameters were properly fine-tuned. Moreover, the impact of the different physical models on the performance of the proposed cell was studied, and it was revealed that band gap narrowing effect was the most significant factor limiting the open-circuit voltage. All the simulations accomplished in this analysis were carried out using the SILVACO TCAD process and device simulators.

Study on amplitude of the noise power spectrum for nano-strained Si NMOSFET

Based on the micro-transport mechanism of total dose to nano-strained Si MOS device, the trapped charge is calculated. By solving the two-dimensional Poisson equation, the channel surface potential is obtained, and the influence of the second-order effect is considered. The bandgap narrowing effect and the short channel effect are considered to obtain high-precision-strained Si threshold voltage of the nano NMOS device.. According to the noise power spectrum amplitude defined in the invention, the trap charge and threshold voltage models are calculated in the invention. The analytical model of correlation between the trap charge of strain Si MOSFET and the amplitude of 1/f noise power spectrum under the total dose effect is derived. The analytical model of correlation between trap charge and 1/f noise power spectrum amplitude constructed by the invention has a simple form, clear physical meaning and high calculation accuracy, which provides a feasible theoretical basis for irradiation reliability and circuit application of strained Si-integrated device.

TiO<sub>2</sub> Photoelectrode Band Gap Modification Using Carbon Quantum Dots (CQDs) for Dye-Sensitised Solar Cells (DSSCs)

In this study, a CQDs at different concentration is used to modify the TiO2 photoelectrode band gap which can improve light absorption of DSSC. The photoelectrode is immersed in different CQDs concentration at 2.5, 5.0, 7.5 and 10 mg/ml to study the effect on TiO2. It was found that photoelectrode with 7.5 mg/ml CQDs was successfully narrowing the TiO2 band gap and generated the highest photocurrent and power conversion efficiency at 17.06 mA/cm2 and 7.23% respectively, compared to pristine TiO2 (PT) at 10.94 mA/cm2 and 4.63% . The band gap narrowing mechanism for CQDs- TiO2 is obtained from the Tauc’s plot method using absorption spectra. The result shows a pristine TiO2 photoelectrode (PT) band gap is 3.38 eV, upon existing of CQDs, the band gap of all photoelectrodes with CQDs at 2.5, 5.0, 7.5 and 10 were reduced to 3.30 eV, 3.28 eV, 3.09 eV, and 3.29 eV respectively. PG 7.5 cell with lowest band gap at 3.09 eV generates effective electron transport from N719 dye to CQDs/ TiO2 layer compared to other photoelectrodes. The band gap narrowing effect is attributed from chemical bonds of Ti-O-C molecules between CQDs/TiO2. Thus, extra energy states are introduced between CQDs and TiO2. The location of these energy will present a quantum confinement effect which narrow the CQDs-TiO2 band gap which extend the light absorption to visible region.

Sulfur-regulated defect engineering for enhanced ultrasonic piezocatalytic therapy of bacteria-infected bone defects

Infection within bone defects remains an intractable issue in clinical practice, causing infectious bone destruction, disability, and death. Facing the deep-seated and refractory characteristics of the infection, an urgent request for rapid in situ sterilization and bone repair therapy is required. In this study, an ultrasound (US)-responsive sulfur-doped (SDBTO) barium titanate (BTO) piezocatalyst is constructed and the relationship between the amount of sulfur dopant and piezocatalysis performance, which is dominant for Staphylococcus aureus (S. aureus) elimination and bone regeneration, is explored. In addition to the band gap narrowing effect, an optimal sulfur doping introduces an appropriate amount of oxygen vacancies to BTO, which can increase the piezoelectric properties and improve the separation of electron-hole pairs, thus endowing SDBTO with outstanding piezocatalytic performance. SDBTO-1 presents superior antibacterial performance with 97.12% antibacterial efficiency against S. aureus. Simultaneously, SDBTO-1, activated by mild medical US, generates a moderate piezoelectric electric signal in vitro and boosts the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) by upregulating the TGF-β signaling pathway. SDBTO-1 successfully cures S. aureus-infected rat tibia bone defects with depressed inflammation and significantly improved bone regeneration. This work offers an effective ultrasonic piezocatalytic therapy through sulfur-regulated defect engineering.

Effect of 150 keV Ti+ ion implantation on the structural, optical, and electrical properties of nonstoichiometric WO2.72 thin films

WO2.72 thin films were deposited on fluorine-doped tin oxide substrates using the e-beam evaporation technique, and 150 keV Ti+ ions were implanted at various fluences. The structural studies of these thin films confirm the presence of P21/m monoclinic phase. After implantation, the intensities of X-ray peaks varied significantly, and atomic force microscopy images revealed changes in grain size with realignments and surface roughness. The redshift observed in the calculated bandgaps is due to the bandgap narrowing effect. The photoluminescence (PL) study shows the decrease in the PL intensity after implantation due to an increase in nonradiative and Auger recombination effects. The electrical studies exhibit the semiconductor to metal transition in Ti-implanted films at the highest ion fluence. The decreasing trend of resistivity, accompanied by the decrease in the carrier concentration, and the higher mobility is understood based on various scattering mechanisms.

Enhanced sunlight driven photocatalytic activity of In2S3 nanosheets functionalized MoS2 nanoflowers heterostructures

Visible light-sensitive 2D-layered based photocatalytic systems have been proven one of the effective recent trends. We report the preparation of a 2D-layered based In2S3–MoS2 nanohybrid system through a facile hydrothermal method, capable of efficiently degrading of organic contaminants with remarkable efficiency. Transmission electron microscopy (TEM) results inferred the attachment of 2D-layered In2S3 sheets with the MoS2 nanoflakes. Field emission SEM studies with chemical mapping confirm the uniform distribution of Mo, In, and S atoms in the heterostructure, affirming sample uniformity. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy results confirm the appearance of 2H-MoS2 and β-In2S3 in the grown heterostructures. UV-DRS results reveal a significant improvement in the optical absorbance and significant bandgap narrowing (0.43 eV) in In2S3–MoS2 nanohybrid compared to pristine In2S3 nanosheets in the visible region. The effective bandgap narrowing facilitates the charge transfer between MoS2 and In2S3 and remarkably improves the synergistic effect. Effective bandgap engineering and improved optical absorption of In2S3–MoS2 nanohybrids are favorable for enhancing their charge separation and photocatalytic ability. The photocatalytic decomposition efficiency of the pristine In2S3 nanosheets and In2S3–MoS2 nanohybrids sample is determined by the decomposing of methylene blue and oxytetracycline molecules under natural sunlight. The optimized In2S3–MoS2 nanohybrids can decompose 97.67% of MB and 76.3% of OTC-HCl molecules solution in 8 min and 40 min of exposure of sunlight respectively. 2D-layered In2S3-MoS2 nanohybrids reveal the tremendous remediation performance towards chemical contaminations and pharmaceutical waste, which indicates their applicability in industrial and practical applications.

Structural, electrical properties and photoluminescence analyses of the terbium doped barium titanate

Multifunctional materials integrating optical and electric properties into a composite or into a doped single–phase material have attracted much attention from scientists for future optoelectronic devices. In this work, polycrystalline Ba1–xTbxTiO3, x = 0.00, 0.01 and 0.05 materials were synthesized by hydrothermal route and their photoluminescence and dielectric properties were studied. The as–prepared powders showed a microstructure consisting of grains with the shape of cube; and average particle size ranging from 75 nm to 150 nm. The investigated temperature dependence of dielectric permittivity of Ba1–xTbxTiO3 ceramics revealed a decrease of the Curie temperature (Tc) with increasing terbium content, and a more pronounced degree of diffuseness of phase transition. The resistivity at room temperature was discussed in terms of positive temperature coefficient of resistance (PTRC) effect. UV–vis reflectance spectra of Ba1–xTbxTiO3 samples showed a decrease of the band gap energy with the increase of Tb amount, due to the band–gap narrowing effect. The photoluminescence spectra recorded for Tb doped BaTiO3 materials, at 80 K, evidenced the typical f–f luminescence lines of the Tb3+ accompanied the broad luminescence band at about 425 nm due to self–trapped exciton recombination. These results demonstrated that the terbium enhances the dielectric properties and photoluminescence simultaneously, being suitable for electronic applications.

Dark-Current-Blocking Mechanism in BIB Far-Infrared Detectors by Interfacial Barriers

We fabricate Ge:B-blocked impurity band (BIB) far-infrared detectors using near-surface processing techniques. The current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> ) characteristics and the energy band structure are investigated. It is found that there are three interfacial barriers in Ge:B BIB detectors due to the bandgap narrowing effect. The barrier height can be adjusted by changing the doping concentration in the contact region of BIB detectors. A new dark-current-blocking mechanism is proposed that the interfacial barriers can block the transport of carriers at low temperatures. Moreover, the greater the barrier height, the stronger the blocking effect. Utilizing this new blocking mechanism, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics of Ge:B BIB detectors can be better explained. By increasing the barrier heights, the dark current is reduced significantly, almost six orders of magnitude within a certain voltage range, and the working temperature is increased from the usual 4.2–10 K, which is of great significance for extending the service life of BIB detectors on outer space observation platforms. Our findings will help to better design BIB detectors and improve their performance.

Structure and electron affinity of the 4H–SiC (0001) surfaces: a methodological approach for polar systems

The ability to accurately and consistently determine the surface electronic properties of polar materials is of great importance for device applications. Polar surface modelling is fundamentally limited by the spontaneous polarisation of these materials in a periodic boundary condition scheme. Surface data are sensitive to supercell parameters, including slab and vacuum thicknesses, as well as the non-equivalence of surface adsorbates on opposite surfaces. Using 4H–SiC as a specific case, this study explores calculation of electron affinities (EAs) of (000) and (0001) surfaces varying chemical termination as a function of computational parameters. We report the impact in terms of band-gap, electric fields across the vacuum and slab for single and double cell slab models, where the latter is constructed with inversional symmetry to eliminate the electric field in the vacuum regions. We find that single cells are sensitive to both slab and vacuum thickness. The band-gap narrows with slab thickness, ultimately vanishing and inducing charge transfer between opposite surfaces. This has a consequence for predicted EAs. Adsorbate species are found to play a crucial role in the rate of narrowing. Back to back cells with inversional symmetry have larger electric fields present across the slab than the single slab cases, resulting in a greater band-gap narrowing effect, but the vacuum thickness dependence is completely removed. We discuss the relative merits of the two approaches.