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Influence of the growth conditions of LT-AlN on quality of HT-AlN growth on Si (111) by metalorganic chemical vapor deposition
摘要： In this study, AlN films on Si(111) using LT-AlN nucleation layer with various conditions at TMAl preflow were grown and investigated. It was shown that the main factor influencing the quality of AlN films is the degree of the substrate coating by aluminium at preflow. The qualitative model of AlN growth using the LT-AlN nucleation layer for three different coverage by Al (high, optimal and low) was suggested. For the film grown under optimal conditions, the rocking curve FWHM for the AlN (0002) reflection was 0.59о. The demonstrated possibility of the high-quality growth of AlN films below 1000oС would be useful for high power electronics.
关键词： B1. Silicon,B1. Aluminum Nitride,B1. Nitrides,B2. Semiconducting III–V materials,A3. Metalorganic chemical vapor deposition,A1. Crystal structure
更新于2025-09-10 09:29:36
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Niobium oxynitride prepared by thermal NH3 nitridation as a photoanode material for solar water splitting
摘要： Niobium oxynitride (NbON) is a promising photoanode material for photoelectrochemical water splitting using visible light up to ~600 nm in wavelength. However, the NH3 nitridation method widely used for oxynitride synthesis cannot convert Nb2O5 (Nb5+) to crystalline NbON (Nb5+), due to the generation of NbOxNy (Nb2+-3+). To prevent Nb reduction during nitridation, we added O2 as an oxidant to the NH3 nitridation reaction system. Investigation of the relationship between O2 concentration and the crystal phase of the resulting samples revealed that Nb2O5 nitridation produces crystalline NbON (Nb5+) within a specific O2 concentration range. The O2 concentration required to synthesize NbON increases from 0.05% to over 0.40% upon increasing the nitridation temperature from 600 °C to 750 °C. The photoelectrochemical properties of NbON films were also investigated. Under simulated sunlight illumination, a NbON photoanode produced a photocurrent of 0.6 mA cm-2 at 1.2 V vs. RHE in H2O2 aqueous solution.
关键词： B. Optical properties,C. X-ray diffraction,D. Electrochemical properties,A. Nitrides,A. Ceramics
更新于2025-09-10 09:29:36
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Influence of quartz on silicon incorporation in HVPE grown AlN
摘要： Aluminum nitride growth via hydride vapor phase epitaxy has been investigated with respect to impurity uptake. The precursor aluminum chloride was identified to react with quartz glass and provide silicon into the reactor atmosphere and subsequently into grown AlN layers. Reactor parts made of quartz were consecutively replaced by carbon glass parts to prevent unintentional silicon incorporation into III-nitride layers during growth. Carbon glass substitution of quartz parts led to a reduction of silicon levels in AlN by three orders of magnitude to 4*1016 cm-3, while carbon concentration in grown AlN layers remained low in the range of 1017 cm-3.
关键词： A1. Substrate,B1. Nitrides,B2. Semiconducting III-V materials,A3. Hydride Vapor Phase Epitaxy,B1. Sapphire
更新于2025-09-09 09:28:46
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Alloy Engineered Nitride Tunneling Field-Effect Transistor: A Solution for the Challenge of Heterojunction TFETs
摘要： Being fundamentally limited to a current–voltage steepness of 60 mV/dec, MOSFETs struggle to operate below 0.6 V. Further reduction in VDD and, consequently, power consumption can be achieved with novel devices, such as tunneling transistors (TFETs) that can overcome this limitation. TFETs, however, face challenges with low ON-current leading to slow performance. TFETs made from III-nitride heterostructures are quite promising in this regard. The lattice mismatch induces a piezoelectric polarization field in a nitride heterojunction that can boost the ON-current. However, it is shown here that the carrier thermalization at the heterointerface degrades the subthreshold characteristics. Therefore, a good design should minimize the number of confined quantum well (QW) states at the heterointerface so as not to degrade the subthreshold characteristics while maintaining the lattice mismatch induced polarization to boost the ON-current. We show here that an InAlN QW on an InGaN substrate alloy engineered TFET design is promising to fulfill these requirements. Proper engineering of the alloy mole fractions and the width of the well can eliminate (or at least minimize) the undesired thermalization effects and, at the same time, provide a lattice mismatch to induce a piezoelectric field for boosting the ON-current. We have used a suitable atomistic quantum transport model to simulate these devices. The model accounts for the different mechanisms that are involved, and captures realistic scattering thermalization effects. This model has been benchmarked in our earlier work with experimental measurements of nitride tunneling heterojunction diodes and is used here to optimize the alloy engineered nitride TFET.
关键词： EQNEQ,band-to-band tunneling (BTBT),phenomenological scattering,nitrides,TFET,tight binding (TB),Atomistic,nonequilibrium Green’s function (NEGF),internal polarization,steep devices
更新于2025-09-09 09:28:46
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Structural, optical and electrical properties of reactively sputtered CrxNy films: Nitrogen influence on the phase formation
摘要： The properties of various CrxNy films grown by direct current (DC) reactive sputtering process with different values of nitrogen partial pressures (0, 2×10-4, 3.5×10-4 and 5×10-4 mbar) were studied. The structural analysis of the samples was performed by using X-ray diffraction and transmission electron microscopy (TEM), while an elemental analysis was realized by means of Rutherford backscattering spectrometry. By varying nitrogen partial pressure the pure Cr layer, mixture of Cr, Cr2N and CrN phases, or single-phase CrN was produced. TEM analysis showed that at pN2 = 2×10-4 mbar the layer has dense microstructure. On the other hand, the layer deposited at the highest nitrogen partial pressure exhibits pronounced columnar structure. The optical properties of CrxNy films were evaluated from spectroscopic ellipsometry data by the Drude or combined Drude and Tauc-Lorentz model. It was found that both refractive index and extinction coefficient are strongly dependent on the dominant phase formation (Cr, Cr2N, CrN) during the deposition process. Finally, the electrical studies indicated the metallic character of Cr2N phase and semiconducting behaviour of CrN.
关键词： spectroscopic ellipsometry,thin films,chromium nitrides,electrical properties,microstructure
更新于2025-09-09 09:28:46
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Compensation effects of high oxygen levels in semipolar AlGaN electron blocking layers and their mitigation via growth optimization
摘要： InGaN-based laser diodes (LDs) grown on the semipolar plane of GaN offer advantages arising from predicted higher gain compared to c-plane devices. However, the performance of semipolar devices has been limited by low injection efficiency. In prior work, this has been proposed to be caused by an inefficient AlGaN electron blocking layer (EBL). A high oxygen level in the EBL found in previous work could cause compensation of the p-type dopants. In this work the oxygen impurities were eliminated via optimizations during the metalorganic chemical vapor deposition (MOCVD) growth. Optimization of the V/III ratio and an increase in the growth temperature during the AlGaN growth was found to reduce the oxygen incorporation. Additionally, residual sources of oxygen were removed from the MOCVD growth process. These combined steps reduced the peak oxygen level in the AlGaN from 5 × 1018/cm3 to 6 × 1017/cm3 as measured by secondary ion mass spectroscopy. LDs were fabricated with and without these modifications to clarify the effect of the reduced oxygen. The threshold current and differential efficiency showed improvement with reduced oxygen. The internal loss and gain of these LDs were measured using the segmented contact method, confirming that the injection efficiency was boosted from 60% with high oxygen to 80% with low oxygen.
关键词： B2. Semiconducting aluminum compounds,A3. Metalorganic chemical vapor deposition,B3. Laser diodes,B1. Nitrides,A1. Impurities
更新于2025-09-09 09:28:46
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Strong suppression of In desorption from InGaN QW by improved technology of upper InGaN/GaN QW interface
摘要： The aim of this work is to elucidate how di?erent growth mode and composition of barriers can in?uence the QW properties and their PL and to ?nd optimal QW capping process, to suppress the In desorption from QWs and to maintain the QW PL e?ciency. It concentrates on the technology procedure for growth of upper quantum well (QW) interfaces in InGaN/GaN QW structure when di?erent temperature for QW and barrier epitaxy is used. We have found that optimal photoluminescence (PL) results were achieved, when the growth after QW formation was not interrupted, but immediately continued during the temperature ramp by the growth of (In)GaN capping layer with small introduction of In precursor into the reactor. Optimal barrier between QW with respect to PL results was found to be pure GaN. We have shown according to SIMS and HRTEM results that by this technological procedure the InGaN desorption was considerably suppressed and three times higher In concentration and two times thicker QWs were achieved for the same QW growth parameters without deterioration of PL intensity in comparison to sample with usually used thin GaN low temperature capping protection. Additionally, for samples covered by the QW capping layer during the temperature ramp the defect band is almost completely missing, thus we can conclude that this defect band is connected with quality of the upper QW interface.
关键词： A1. Interfaces,A3. Quantum wells,B1. Nitrides,A3. MOVPE,B2. Scintillators
更新于2025-09-04 15:30:14
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Structural characteristics of m-plane AlN substrates and homoepitaxial films
摘要： Homoepitaxial non-polar AlN films were realized on m-plane (1010)-oriented AlN single crystals by metalorganic chemical vapor deposition (MOCVD). The microstructural properties of m-plane AlN substrates and homoepitaxial films were assessed by means of atomic force microscopy and high resolution x-ray diffraction characterization. Results indicated that both m-plane AlN substrates and films possessed exceptional structural quality, with some anisotropic mosaic distributions due to the quasi-bulk nature of the non-polar single crystals. An increase in the MOCVD growth temperature was noted to minimize the degree of inherited mosaic anisotropy without altering the m-plane AlN film growth rate, indicating that high temperature growth is critical to produce optimal film crystallinity. A dramatic change in the film surface morphology from heavily faceted “slate-like” features to monolayer steps was observed as the growth temperature was increased. The “slate-like” surface morphology produced low intensity cross-streaks in symmetric (1010) reciprocal space maps, tilted about 18° away from the (1010) crystal truncation rod. The orientation of these diffuse streaks corresponds to the physical alignment of the slates with respect to the substrate surface normal. X-ray line scans and defect-selective reciprocal space mapping confirmed that these low intensity streaks are solely dependent on this peculiar surface structure produced at low MOCVD growth temperatures and unrelated to basal plane stacking faults or other extended defects. All observations confirm that high quality III-nitride epitaxial structures on m-plane AlN substrates are attainable with controllable MOCVD growth processes, as demanded for future high performing AlN-based non-polar devices.
关键词： Characterization,Metalorganic chemical vapor deposition,High resolution x-ray diffraction,Surface structure,Nitrides,Crystal structure
更新于2025-09-04 15:30:14
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Polydopamine and Barbituric Acid Co-Modified Carbon Nitride Nanospheres for Highly Active and Selective Photocatalytic CO <sub/>2</sub> Reduction
摘要： Carbon nitride nanospheres modified with polydopamine and barbituric acid (BA-CNS-PDA) were successfully prepared by following a template-copolymerization and post-modification strategy. The photocatalytic CO2 reduction was carried out using BA-CNS-PDA as photocatalyst, Co(bpy)3 as the cocatalyst and TEOA as the sacrificial electron donor. The productivity and selectivity for photocatalytic reduction of CO2 to CO on BA20-CNS-PDA15 under visible-light for 4 h were measured to be 158 μmol and 86.0 %, respectively, and are nearly 5 and 1.5 times, respectively, that of unmodified CNS. Optical characterization indicates that the outstanding photocatalytic CO2 reduction performance is a result of improved charge separation and transfer due to copolymerization with barbituric acid and enhanced visible light absorption due to polydopamine. The adsorption isotherm of CO2 demonstrates that polydopamine increase CO2 adsorption capacity and promote CO2 activation due to the presence of the amino groups.
关键词： Photocatalysis,Nitrides,CO2 reduction,Nanostructures
更新于2025-09-04 15:30:14