Papers by Keyword: Nitrogen Doping

Abstract: High-performance ultraviolet photodetectors require high sensitivity, fast response, strong radiation resistance, and high on/off ratio. This study investigates the impact of in-situ nitrogen doping on the performance of Silicon Carbide ultraviolet photodetectors (SiC-UVPDs). The SiC-UVPD devices demonstrated high sensitivity, fast response, low dark current, and good stability. Notably, the sensitivity of the devices increased with higher nitrogen doping, reaching 1.94 × 10⁵ % for the 8-sccm nitrogen-doped SiC-UVPD under 254 nm UV light illumination at 20 V - a 51% improvement compared to undoped SiC-UVPDs. Furthermore, nitrogen doping did not compromise the devices' response speed. Consequently, the combination of high sensitivity, fast response, low-cost fabrication, and robust radiation resistance positions SiC-UVPDs as promising candidates for high-performance ultraviolet photodetectors, particularly in harsh environment applications.

Abstract: This study investigates the multifaceted relationships between key process parameters such as C/Si ratio, system pressure, temperature, and growth rate and their effects on nitrogen dopant incorporation in homoepitaxial layers on 4H-SiC substrates. We focus on understanding how these growth parameters influence the in situ nitrogen incorporation during chemical vapor deposition (CVD) of epitaxial layers on 150 mm commercially available SiC substrates. Through a carefully designed experimental framework, which explores the interactions between each parameter and the C/Si ratio, we have shed light on a refined approach for epitaxial growth. This approach may not only stabilize the nitrogen dopant concentration across the wafer but possibly also reduces the formation of epitaxial defects.

Abstract: Proton Exchange Membrane Fuel Cell is a promising green energy conversion machine. However, some drawbacks, such as Pt corrosion on the cathode side, the high price of Pt, Nafion membrane, and the need for the high precision assembly process, limit their commercialization. In this study, PtCrCo alloy which is supported by nitrogen-doped activated carbon was synthesized by facile method to increase electrochemical performance as a cathode catalyst and reduce Pt catalyst usage. Nitrogen-doped Activated Carbon/PtCrCo/Nitrogen-doped Carbon (NAC/PtCrCo/N) catalyst was investigated to analyze the effect of increasing the composition of nitrogen-doped activated carbon in the synthesis process on the morphology and electrochemical performances of the catalyst. Polyaniline (PANI) as Nitrogen precursor was added to Activated Carbon (AC) powder with ratio of AC to PANI; 1:0, 3:1, 1:1, 1:3, as called AC, NAC1, NAC2, and NAC3 respectively. The catalyst synthesis process is carried out with the four activated carbon supports. Material characterizations were carried out using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Brunauer-Emmett-Teller (BET), Cyclic Voltametry (CV), and Linear Sweep Voltametry (LSV). The XRD measurement shows that the addition of nitrogen doping tends to reduce the diffraction peak intensity of nitrogen-doped activated carbon compared to the pristine carbon. The doping also increases the surface area of the activated carbon as measured by the BET method. Nitrogen doping increases the conductivity and the addition of alloys can add better stability and catalytic activity for cyclic voltammetry results of the four catalysts cannot be calculated. The NAC3/Pt-Cr-Co/N electrocatalyst exhibited the highest initial potential at ~1 mAcm^-2 of 0.997 V compared to the other four samples. On the other hand, AC/Pt-Cr-Co/N catalyst has the highest current density value of 22.156 mAcm^-2.

Abstract: A method for mitigating loss of conformational stability in 150 mm n-type 4H SiC wafers was investigated. Modifications to the physical vapor transport (PVT) process used to grow the parent bulk crystals, combined with post-growth thermal treatment, were examined as means of reducing the internal stresses hypothesized to promote instability. The magnitude of the stresses was analyzed by mechanically thinning sets of wafers produced from each process to determine the critical thickness of stability loss. The average critical thickness was found to be reduced by 13% via growth cell modification, at a reduced level of thermal treatment relative to a control process, with all wafers becoming unstable greater than 30 μm below the minimum recorded production thickness. Assessment of the spatial uniformity of dislocations indicated that lower conformational stability corresponded to elevated densities of basal plane dislocations (BPDs) and threading edge dislocations (TEDs) at the wafer edge relative to the center.

Abstract: This work studies the variation of the defects density of in situ doped 3C-SiC layers during heteroepitaxial Chemical Vapour Deposition (CVD). A review on the evolution of defects density as a function of 3C-SiC grown thickness, for different N doping concentrations is offered. The doping range spanned in the experiment suits the realization of power devices.The outcome of this work provides an explanatory picture of the significant drop in stacking faults density by roughly an order of magnitude through the N doping at concentrations of the order of ~2.9×10¹⁹ cm^-3 during the growth. Conversely, N doping shows to favor the development of dislocation-like defects within the crystalline matrix. However, in few um, the crystal is able to display an effective dislocation closure mechanism, which rapidly recovers crystal quality.

Abstract: The scratch damage that caused the generation of double Shockley stacking faults (DSFs) in heavily nitrogen doped 4H-SiC crystal was investigated quantitatively. Scratch tests were carried out on 4H-SiC substrates with a nitrogen concentration of 2.6 × 10¹⁹ cm^-3. A residual tensile stress of 40 MPa was detected around the scratch loaded at 30 mN with a diamond tip. DSFs were generated from this scratch by annealing at 1100°C for 2 h in Ar atmosphere. After annealing, the residual stress around the scratch was reduced to a tensile stress of 10 MPa. This result suggests that the reduction of residual stress around the scratch coincided with the formation of DSFs.

Abstract: Shifts in the spatial distribution of threading dislocations in 150 mm 4H SiC wafers were examined as a response to intentional changes in both the flow of the nitrogen source gas used to control resistivity during bulk crystal growth, and the growth rate. The density of threading edge and screw dislocations was found to be more evenly distributed in wafers produced under a high-growth rate, low-resistivity process. This result corresponded to a flattening of the resistivity distribution, and a ~34% reduction in on-and off-facet resistivity differential. The effect was attributed to regularized 4H island coalescence due to modulation of step terrace width.

Abstract: Low field electron mobility in heavily nitrogen doped 4H-SiC epitaxial layers as well as in the regions formed by ion implantation was extracted from Hall and van der Pauw measurements. The measurements were done at room temperature in 4H-SiC samples with carrier concentrations ranged from 2.8×10¹⁸ to 2.3×10¹⁹ cm^-3. Fitting parameters in empirical expression given by Caughey and Thomas for room temperature low field electron mobility depending on carrier concentration in 4H-SiC were extracted.

Abstract: SrAl₂O₄:Eu²⁺,Dy³⁺ long-lasting phosphors were incorporated AlN successfully by a conventional solid-state reaction in the reductive atmosphere. When a certain amount of AlN was doped, the specimen SrAl₂O_4-3xN_2x: Eu²⁺, 0.01Dy³⁺ (x = 0.0-0.2) maintained the phase purity. Under the excitation at 398nm, an intense broadband emission centered at 514 nm, originating from the 4f⁶5d¹→4f⁷ transition of Eu²⁺, was observed. It is noteworthy that partial nitridation leads to an enhancement in the emission intensity up to 240%. The study of thermal stability shows that the intensity of SrAl₂O_3.55N_0.3:Eu²⁺,0.01Dy³⁺ phosphor still remains 72% at 150 °C comparing with the initial, while only 62% for the un-doped phosphor. Taking enhanced photoluminescence (PL) property and good thermal stability into account, SrAl₂O_4-3xN_2x:Eu²⁺, 0.01Dy³⁺ is a promising candidate for the phosphors used in alternating current (AC) LEDs.

Abstract: We investigated the spatial distribution of carrier concentration in n-type 4H-SiC grown by the solution method from the peak frequency of the longitudinal optical phonon-plasmon coupled (LOPC) mode of the Raman spectra on the surface. The carrier concentration at the position of the smooth terrace was higher than the carrier concentration at the position where the macrosteps were formed. This indicates the nitrogen incorporation efficiently occurs on the smooth surface where the density of macrosteps is relatively low. The different incorporation of nitrogen depending on the surface morphology can be understood from the view point of the adsorption time of impurity on the terrace. The present result implies that the uniform surface morphology is necessary to achieve uniform doping concentration in SiC crystal.