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Dr. Zongwei Xu is Associate Professor for College of Precision Instrument & Opto-electronics Engineering at Tianjin University, China. Zongwei Xu received his Doctoral Degree in Mechanical Manufacture and Automation from Harbin Institute of Technology, China in 2007. As Principal Investigator (PI), Four National Natural Science Foundation of China (NSFC) projects have been granted, including one International Cooperation and Exchange project. Dr. Xu has published more than 50 papers, 5 book chapters, 14 patents. He was invited as Guest Editor for Current Nanoscience, book Section Editor for Springer. He was selected as a representative by Chinese academy of engineering (CAE) in 2015, participated "4th China-America Frontiers of Engineering Symposium" organized by CAE and US National Academy of Engineering (NAE) and "1st Indo-Chinese Young Engineering Leaders' Conclave (ICON-1)" organized by CAE and Indian National Academy of Engineering (INAE). He was granted with "Young Researchers" Award in the 3rd Asian Precision Engineering and Nanotechnology International Conference (ASPEN), Japan, 2009. He was the academic or organization committee member for 8 International conferences. He gave 8 Invited talks at international conferences.
P-type doped 4H-SiC with very low resistivity is still one challenging technology in semiconducting fields. It is well accepted that p-type doping of 4H silicon carbide (SiC) by Al implantation and subsequent annealing results in free charge carrier concentrations which are significantly below what would be expected from activated and ionized Al concentrations. This is commonly explained by so-called compensating defects induced during the implantation process and which remain after annealing. Here, the experimentally determined compensation ratio (i.e., the ratio of defect concentration to activated Al concentration) is increasing with decreasing Al concentration. Obviously, this compensation significantly hinders the fabrication of todays and future SiC electron devices where both, fabrication of regions with moderate p-doping concentrations (such as p-well regions or junction determination structures) where accurate concentrations are required as well as regions where very high doping concentrations (e.g., ohmic contacts) are required. In this talk, Molecular Dynamics (MD) simulations, Raman spectroscopy and sheet resistance measurements were used to study the preparation processes of low-resistance p-type 4H-SiC by Al ion implantation with ion doses of 2.45×1012 - 9.0×1014 cm-2 and annealing treatment with temperatures of 1700 - 1900 °C. Greatly different from the LOPC (longitudinal optical phonon-plasmon coupled) Raman mode found from the sample of doping 4H-SiC during epitaxial growth, no significant influence on the surface concentration could be found for the longitudinal optical (LO) mode of Al-implanted 4H-SiC samples. When the Al surface concentration is larger than around 1018 cm-3, it was found that the intensity of the LO+ Raman peak (~ 980 - 1000 cm-1) increases and its full width at half maximum (FWHM) drops with the increase of surface concentration after annealing treatment. Moreover, for surface concentrations above 1018 cm-3, the LO+ Raman peak showed a left shift towards the LO peak, which could be related to the increase of free carrier concentration in the Al-implanted 4H-SiC samples. After higher annealing temperatures of 1800 °C and 1900 °C, the crystallinity of Al-implanted 4H-SiC was found to be improved compared to annealing at 1700 °C for surface concentrations larger than 1018 cm-3, which is consistent with the results of sheet resistance measurements.