MATERIALS SCIENCE AND ENGINEERING

DMSE Colloquia, Fall 2009

Tuesday, September 22, 2009 | 10:00 AM | 411 White Building

Colorful, Misbehaving Defects:
On the Luminescence and Driving Force of Stacking Fault Motion In SiC

Joshua D. Caldwell

Physical Scientist
U.S. Naval Research Laboratory
Washington, D.C. 20375
U.S.A.

Abstract:

Over the past decade, a significant effort has been put into understanding the structural, electrical, luminescence properties of various defects within hexagonal SiC. Perhaps the most puzzling and damaging defect found within this promising material has been the recombination-induced stacking fault (SFs), which nucleates at basal plane dislocations (BPDs). These SFs have been observed to nucleate and expand due to the injection of electron-hole pairs during forward bias operation of a bipolar SiC device, such as a pin diode. This SF expansion in turn induces a drift in the forward voltage drop (V_f), causing the turn-on voltage for the device to continuously shift to higher values during operation. Understanding the primary driving force for SF nucleation and expansion has thus become a primary focus of numerous research groups in an effort to alleviate their deleterious effects. Up until recently, the reported driving force models were all based on the hypothesis that SFs were thermodynamically stable with respect to the 4H-SiC host lattice.¹ Therefore, these prior models tended to focus on explaining the reason for the improved stability of the material in the faulted state and provided little hope that their effects could be sufficiently minimized without the complete eradication of the BPDs from the epitaxial material. However, annealing² and high temperature device operation³ experiments have clearly shown that SFs can also contract, inducing a full recovery of the initial electrical characteristics of the device. Thus SFs are not the preferred state of 4H-SiC in the absence of injected electron-hole pairs and SF motion and their impact can be mediated by varying the injected electron-hole pair density and/or the operating temperature.
Here, we introduce and discuss a possible mechanism describing the primary driving force governing SF expansion and contraction that is consistent with our previously reported experimental observations. We will also present further experimental and simulation results that strengthen the support for this model. These simulation results imply that SF-induced degradation of the V_f is due to a reduction in the carrier lifetime within the SFs. Finally, we investigate some of the interactions observed between the growing SFs and other extended defects within the lattice and as well as explore some interesting changes in the luminescence properties of these defects during the expansion process.

References
1 M. E. Twigg, R. E. Stahlbush et al., Appl. Phys. Lett. 82, 2410 (2003); S. Ha, M. Skowronski et al., Phys. Rev. Lett. 92 (17), 175504 (2004); W. R. L. Lambrecht and M. S. Miao, Phys. Rev. B 73 (15), 155312 (2006).
2 J. D. Caldwell, R. E. Stahlbush et al., Appl. Phys. Lett. 90 (14), 143519 (2007); T. Miyanagi, H. Tsuchida et al., Appl. Phys. Lett. 89 (06), 062104 (2006).
3 J. D. Caldwell, O. J. Glembocki et al., Appl. Phys. Lett. 91, 243509 (2007).

Speaker Biography:

Dr. Joshua Caldwell graduated from Virginia Tech with a B.A. in Chemistry and Minor in History in 2000. During this time he worked as a manufacturing engineer for ITT Industries Night Vision, working on the next generation of Night Vision Goggles for the U.S. Military. Following this, he began work at the University of Florida in Physical Chemistry, where he studied electron-nuclear interactions in low-dimensional electron structures via magnetic resonance. Upon earning his Ph.D. in 2004, he accepted an ASEE postdoctoral position at the U.S. Naval Research Laboratory in Power Electronics, after which he became a permanent staff member in 2007. At NRL he has studied defects in wide-bandgap semiconductors, graphene materials characterization and plasmonic and photonic nanostructures.

Coffee and doughnuts will be served from 9:30 AM.

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