MSE Colloquium - Prof. Patricia Mooney
Date: February 24, 2012 from 2:00 pm to 3:00 pm EST
Location: Room 214, S. W. Mudd
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to wjh2121@columbia.edu or by calling 2128547860.
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P.M. Mooney
Professor and Tier 1Canada Research Chair
Physics Department, Simon Fraser University, Burnaby, BC, Canada

"Effects of N Incorporation on Defects at SiO2/SiC Interfaces"


Wide bandgap semiconductors are under intense investigation for high power devices with improved energy efficiency for applications such as power transmission and solar energy conversion. As well as the wide bandgap (3.26 eV for 4H-SiC) and corresponding high breakdown voltage, an advantage of SiC is that, as for Si, a very high quality thermal oxide can be grown on SiC. However, implementation of SiO2/SiC MOSFETS for high power applications has been hindered by the high density of defect electronic states near the SiO2/SiC interface. To investigate insulator/semiconductor interfaces, we have developed a method to distinguish the energy and spatial distribution of near interface defects through a comparison of the thermal emission energy extracted from constant capacitance transient spectroscopy (CCDLTS) measurements and the interface Fermi energy (FP), determined from temperature-dependent 1MHz C-V curves. We have applied this method to investigate nitrogen passivation of interface defects leading to improved SiC MOSFET channel mobility.


NO-annealing following thermal oxidation was found to decrease the SiO2/SiC interface state density by a factor of 10. Electron capture by tunneling was observed and the difference in defect energy levels with respect to the SiC bandgap in 4H-SiC and 6H-SiC is consistent with the conduction band offsets of the two polytypes at the SiO2/SiC interface, thus leading to the conclusion that the traps passivated by N are oxide traps. Comparison with results from first principles calculations suggests that the observed oxide traps are CO=CO and interstitial Si. SiC defects that are not affected by NO-annealing are suggested to be carbon di-interstitial defects, (C2)i, introduced by in-diffusion of C during oxidation.N implanted near the SiC surface prior to oxidation is less effective in reducing the density of oxide traps. The higher channel mobility in N pre-implanted transistors is due at least in part to activation of a small fraction of the implanted N near the SiO2/SiC interface as donors in SiC during oxidation, thus reducing the effects of interface trapping. In addition, the absence of the oxidation-induced SiC defects may contribute to the improved mobility in N pre-implanted transistors. Well-known traps introduced in SiC by ion-implantation are also observed in 4H-SiC MOS capacitors fabricated by N pre-implantation, thus validating this new characterization method.