7/11/2023 0 Comments Psu crystalmakerHelically coiled carbon nanotubes as supercapacitor electrodesĭespite their low specific surface area (500 m 2 g -1) relative to that of activated carbon (1500–2000 m 2 g -1), carbon nanotubes are attractive as effective electrode materials for supercapacitors. The doping dependence of the thermal conductivity of bulk gallium nitride substrates. Song, Y., Lundh, J., Wang, W., Leach, J., Eichfeld, D., Krishnan, A., Perez, C., Ji, D., Borman, T., Ferri, K., Maria, JP., Chowdhury, S., Ryou, J., Foley, B., Choi, S. The results provide useful information for designing thermal management solutions for vertical GaN power electronic devices. This suggests that phonon-disclocation scattering dominatnes over phonon-impurity scattering in the tested HVPE-grown bulk GaN substrates. While doping is evidenced to reduce the GaN thermal conductivity, the highest thermal conductivity (201 W/mK) is observed in a heavily doped Si-doped (1-5.00 x 10 18 cm 3) substrate with the highest crystalline quality. Using this comprehensive suite of characterization methods, the interrelation among structural/electrical parameters and the thermal conductivity of bulk GaN substrates was investigated. Structural and electrical characterization methods including x-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS), Raman spectroscopy, and Hall-effect measurements were used to determine and compare the GaN crystal quality, dislocation density, doping level, and carrier concentration. In this work, a steady-state thermoreflectance (SSTR) technique was used to measure the thermal conductivity of HVPE-grown GaN substrates employing different doping schemes and levels. Hence, it is of crucial importance to measure and understand how the dopant type (Si, Fe, and Mg), doping level, and crystal quality alter the thermal conductivity of HVPE-grown bulk GaN. Vertical device structures consist of GaN layers of diverse doping levels. Halide vapor phase epitaxy (HVPE) is currently the most common approach for manufacturing commercial GaN substrates used to build vertical GaN transistors. Unfortunately, the higher power density of GaN electronics inevitably leads to considerable device self-heating which impacts device performance and reliability. Recent efforts have focused on realizing vertical power device structures such as in-situ oxide, GaN interlayer based vertical trench metal-oxide-semiconductor field-effect transistors (OG-FETs). Gallium nitride (GaN ) has emerged as one of the most attractive base materials for next-generation high-power and high-frequency electronic devices. The doping dependence of the thermal conductivity of bulk gallium nitride substrates Investigation of phase evolution within ZnO-Bi 2O 3 varistors utilizing thin film prototypes. Lastly, we began correlating as-deposited Bi 2O 3 phases with resulting electrical behavior and found on average, a 12x difference between nonlinear coefficients for γ *- and β *-BZO.įerri, K., Paisley, E., DiAntonio, C., Han, S-W., Chu, R., Maria, J-P. Next, we explored post heat-treated (Mn:ZnO)-Bi 2O 3 stacks. Subsequently we developed a saturated front model, based on Zn-out diffusion, which correlates changes in Bi 2O 3 thickness to phase evolution. Characterizing interactions between Bi 2O 3 films deposited on thin film and single crystal ZnO by XRD and TEM-EDS revealed primarily Zn-out diffusion, resulting in two (Bi 2O 3) 1-x(ZnO) x phases. To circumvent these challenges in the ZnO-Bi 2O 3 varistor system, we use as-deposited and post heat-treated thin film ZnO-Bi 2O 3 prototypes to simulate bulk varistor grain boundary phase formation and investigate resulting defect chemistry. Bulk studies are challenging due to random grain boundary formation and difficulties studying individual boundaries. While barrier heights can be modulated with formulation and defect chemistry, mechanisms by which dopant locations, defect compensation, and local phases determine varistor behavior is not completely understood. The prototypical ZnO-Bi 2O 3 varistor system forms electrostatic Schottky barriers at grain boundaries in response to residual Bi and other dopants left at grain surfaces during Bi 2O 3 segregation. Varistors are technologically important for their large energy handling capabilities and highly nonlinear electrical behavior when voltages above a characteristic switch field are applied. Investigation of phase evolution within ZnO-Bi 2O 3 varistors utilizing thin film prototypes
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