Search

The p-type 4H-SiC are ideal materials of substrate for high-power electronic devices. However, p-type 4H-SiC single crystal substrates with high quality, large size and low resistance could not be produced in China due to technological constraints. In this paper, Al doped p-type 4H-SiC single crystal substrates with a diameter of 4-inch were prepared by physical vapor transport (PVT). Dislocation defects were tested by the corrosion of KOH on the substrate. The crystal quality was characterized by high resolution X-ray diffraction (HRXRD), the crystal polytype was determined by Raman spectrum scanning, and the resistivity was measured by non-contact resistivity tester, respectively. It suggest that as-prepared substrates with low overall dislocation density and total resistivity (less than 0.5 Ω·cm) are prepared, meanwhile their crystal quality are good and crystal polytype is stable. Furthermore, the energy band structure and density of states of pristine 4H-SiC and Al doped p-type 4H-SiC were calculated via the first-principles plane wave ultra-soft pseudopotential method. The results show that the gap width decreases and the Fermi level passes through the valence band after the introduction of Al, which is considered as the characteristics of a p-type semiconductor. This elaborate study pave the way for the large-scale production of the p-type 4H-SiC substrate with high quality and low resistance. [ABSTRACT FROM AUTHOR]

A strong chiral near-field plays significant roles in the detection, separation and sensing of chiral molecules. In this paper, a simple and symmetric metasurface is proposed to generate strong chiral near-fields with both circularly polarized light and linearly polarized light illuminations in the mid-infrared region. Owing to the near-field interaction between plasmonic resonant modes of two nanosheets excited by circularly polarized light, there is a strong single-handed chiral near-field in the gap between the two graphene nanosheets and the maximum enhancement of the optical chirality could reach two orders of magnitude. As expected, the intensity and the response wavelength of the chiral near-fields could be controlled by the Fermi level and geometrical parameters of the graphene nanosheets, as well as the permittivity of the substrate. Meanwhile, based on the interaction between the incident field and scattered field, the one-handed chiral near-field in the gap also could be generated by the linearly polarized light excitation. For the two cases, the handedness of the chiral near-field could be switched by the polarized direction of the incident light. These results have potential opportunities for applications in molecular detection and sensing. [ABSTRACT FROM AUTHOR]