AVS 51st International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuA

Invited Paper EM-TuA3
In situ Studies of Stacking Fault Formation in Silicon Carbide

Tuesday, November 16, 2004, 2:00 pm, Room 304B

Session: Defects and Interfaces in Electronic Materials and Devices
Presenter: A. Galeckas, Royal Institute of Technology, Sweden
Authors: A. Galeckas, Royal Institute of Technology, Sweden
J. Linnros, Royal Institute of Technology, Sweden
P. Pirouz, Case Western Reserve University
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Silicon carbide (SiC) has long been recognized as one of the leading semiconductors for high-power applications. Recently, commercial implementation of 4H-SiC material in high-voltage bipolar electronics has seriously been obstructed by a phenomenon causing degradation of electrical characteristics. In this paper we will address the internal causes of degradation by presenting an overview of in situ studies of structural instabilities within active area of SiC device. Several applications of a novel time-resolved pump-probe imaging spectroscopy technique, recently developed by our group for studies of stacking fault (SF) nucleation and expansion dynamics, will be presented in conjunction with conventional TEM measurement results. More specifically, in our method an intense optical excitation is employed to provide excess carriers and to trigger recombination-enhanced motion of dislocations (REDM), whereas dynamics of defects is monitored by time-lapse imaging of the background luminescence, set by a low-intensity probe cw-excitation. We report optically induced nucleation, multiplication and rapid expansion of SF defects and provide experimental evidence of their detrimental impact on carrier transport properties. Our results show that degradation phenomenon is not restricted to the device’s active area – stacking faults likewise nucleate and expand on the outside as well as in the standalone epilayers. This fact essentially discards common assumptions that heavy doping of P+ layer and residual mechanical stress at P+/N junction are almost certain SF nucleation sources. In contrast, statistical analysis of PL imaging results strongly suggests that the pre-existing growth defects, for the most part threading screw dislocations, are the major nucleation sources of SFs. Temperature and excitation dependencies of optically stimulated dislocation glide have been quantified, providing an activation enthalpy of 0.25±0.05 eV, which is consistent with energy estimated from the electrical REDM experiments. We discuss the observed differences of glide velocities in terms of possibly different origin of dislocation partials (silicon-core versus carbon-core) and propose the anti-phase defects (APD) on the dislocation partials as likely sites for the kink-pair nucleation. Finally, in view of the important experimental observation that similar formations of SFs could be optically-induced also in p-type material and in 6H polytype, we conclude that degradation phenomenon seems to be rather a general problem of hexagonal SiC material than that of a bipolar device.