Papers by Keyword: High Resistivity

Abstract: In this study, we tried to grow SiC ingots with high resistivity and polytype stability with adoption hydrogen mixed gas flow to the PVT method. Three different types of growth atmosphere of N₂+Ar, H/Ar ratio:10% and 30% were employed. The polytype inclusion, crystal shape and transparency, and their resistivity were systematically investigated by UVF images, exposing backlighting, and high resistivity analysis using COREMA (Contactless Resistivity Mapper), respectively. The SiC ingot grown with adoption N₂+Ar exhibited a suppression of polytype inclusion, a convex shape and a lower resistivity. In contrast, the SiC ingot with more higher H/Ar ratio of 30% than that of 10% shows no polytype inclusion and highest resistivity of 1.7E11mΩ∙cm. The growth atmosphere of relative higher H/Ar ratio in SiC crystal growth could be led the way to manufacture HPSI (high-purity semi-insulating)-SiC single crystal with polytype stability.

Abstract: A series of [Fe₈₀Ni₂₀-O/ZnO]_n multilayer thin films with different ZnO separate layer thicknesses (t, from 0 to 3 nm) and fixed Fe₈₀Ni₂₀-O layer thickness (about 5 nm) have been fabricated on (100)-oriented silicon wafers and glass substrates by reactive magnetron sputtering. Microstructure analysis and static magnetic measurement results indicate that the magnetic properties of the films can be adjusted by the variation of ZnO monolayers thickness. All films reveal an evident in-plane uniaxial magnetic anisotropy (IPUMA). The values of in-plane uniaxial magnetic anisotropy fields (H_k) and resistivity (ρ) can be changed from 8 to 57 Oe and 62 to 168 μΩ•cm respectively with the t increasing. While the values of hard axis coercivity (H_ch) and easy axis coercivity (H_ce) reveal minimums of 1.5 and 3 Oe respectively at t = 1 nm.

Abstract: Zinc Ferrite (ZF) nanopowders relatively uniform size distributions ranging from 5 to 14 nm were prepared by solution combustion and hydrothermal methods. The PXRD showed cubic phase, spinel structure, and particle size in nanoscale. The SEM images confirm the agglomeration of the product composed of uniform nanoparticles of flakes type and spherical type in combustion and hydrothermal methods respectively. The purity check was done by FTIR. The optical band gap energy (Eg) obtained by UV-Vis spectra of the ZF nanopowders prepared by solution combustion and hydrothermal methods were found to be 1.985 eV and 1.99 eV respectively. The present study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles are strongly affected by the synthesis method used. Results suggest that the electrical properties depend on the particular method of preparation and sintering temperature of the prepared samples. The resistivity of the samples increased to the order of 103 by sintering the samples. It is observed that the activation energy (Ea) decreases with increasing the sintering temperature.

Abstract: The continuous 1.0 µm GaN epilayers with and without partially Mg-doped were grown on Si (111) substrates by metal organic chemical vapor deposition (MOCVD). The DC current-voltage (I-V), time-of-flying secondary ion mass spectrometer (ToF-SIMS) and atomic force microscope (AFM) measurements were employed for comparison to characterize surface morphology and resistivity of GaN buffer layer with and without partially Mg-doped. The sample of 1.0 µm GaN epilayer with partially Mg-doped shows much higher resistivity than sample without Mg-doped, which indicates the partially Mg doping in 1.0 µm GaN epilayer can effectively increase the resistivity of GaN grown on Si (111) substrates. As a result, the high resistivity GaN buffer layer with good surface morphology is achieved in the partially Mg-doped GaN buffer layer.

Abstract: Unintentionally doped GaN were grown on Si (111) substrates by metal organic chemical vapor deposition (MOCVD). The high-resolution X-ray diffraction (HRXRD) and Lehighton contactless sheet resistance measuring systems were employed to characterize the quality and sheet resistance (R_s) of GaN epilayer. The threading dislocation density (TDD) was estimated by calculating the full width at half maximum (FWHM) of GaN (0002) and (10-12) diffractions measured by HRXRD. The relationship between R_s and TDD in GaN epilayer was investigated. The influence of growth conditions of bottom GaN initial layer including carrier gas category (H₂ or N₂), growth temperatures, and growth pressures on the quality or resistivity of top GaN epilayer was discussed and analyzed. As a result, the improved resistivity was achieved in top GaN epilayer with low TDD by using H2 carrier, low growth temperature of 1050°C, and high growth pressure of 400mbar during the growth of bottom GaN initial layer.

Abstract: The concept of fully encapsulated, semi-insulating silicon (SI-Si), Czochralski-silicon-on-insulator (CZ-SOI) substrates for silicon microwave devices is presented. Experimental results show that, using gold as a compensating impurity, a Si resistivity of order 400 kΩcm can be achieved at room temperature using lightly phosphorus doped substrates. This compares favourably with the maximum of ~180kΩcm previously achieved using lightly boron doped wafers and is due to a small asymmetry of the position of the two gold energy levels introduced into the band gap. Measurements of the temperature dependence of the resistivity of the semi-insulating material show that a resistivity ~5kΩcm can be achieved at 100°C. Thus the substrates are suitable for microwave devices working at normal operating temperatures and should allow Si to be used for much higher frequency microwave applications than currently possible.