Microstructural Aspects and Mechanism of Degradation of 4H-SiC PiN Diodes under Forward Biasing

Abstract

Devices fabricated from the wide bandgap semiconductor SiC have many advantages over those made from conventional semiconductors. Thus, performance characteristics of some 4H-SiC devices can be two orders of magnitude better than equivalent devices made from silicon. On the other hand, new and unexpected problems have emerged with the operation of some SiC devices that need to be understood and solved before further progress can be made in this area. One of the most intriguing problems has been the degradation of bipolar PiN diodes that have major advantages over unipolar Schottky barrier diodes at high blocking voltages. The electrical degradation of the PiN diodes refers to a drop in voltage under extended forward current operation. The degradation appears to be associated with the appearance of stacking faults (SFs) in the entire base region of the diode. In this paper, we discuss some puzzling aspects of stacking fault formation in such diodes. Electroluminescence as well as TEM has been used to investigate the degradation problem and, based on experimental results, the formation of stacking faults within the device, possible sources of partial dislocations responsible for the stacking faults, and the enhanced motion of dislocations under forward biasing are considered.

Combined photoluminescence-imaging and deep-level transient spectroscopy of recombination processes at stacking faults in4H−SiC

“…2,3 Studies show that degradation in the active region of forward operating devices is caused by spontaneous formation of planar defects, 4,5 identified as basal plane stacking faults ͑SF͒ bounded by Shockley partial dislocations ͑PD͒. 6,7 The phenomenon of recombination enhanced dislocation glide ͑REDG͒, 5,8 also known as the "phonon-kick" mechanism, 9,10 is believed to be responsible for the lateral expansion of SFs. Part of the electron-hole ͑e-h͒ recombination energy is redirected into nonradiative sites along the dislocation line to aid formation and migration of kinks, thus dramatically reducing the activation barrier for glide.…”

“…Part of the electron-hole ͑e-h͒ recombination energy is redirected into nonradiative sites along the dislocation line to aid formation and migration of kinks, thus dramatically reducing the activation barrier for glide. 8,10 Apart from this strong REDG effect, theoretical models interpret an SF in 4H-SiC as a two-dimensional ͑2D͒ quantum well ͑QW͒ for the conduction band electrons. 11,12 Since entrapment of electrons in the QWs leads to reduction of the mean electronic energy, a faulted n-type crystal is supposed to be more stable than a perfect one.…”

Investigation of Electron–Hole Recombination-Activated Partial Dislocations and Their Behavior in 4H-SiC Epitaxial Layers

“…As we know, the partial dislocations usually consist of 30°or 90°segments lying along their Peierls valley directions. The 90°s egment moves much faster 17 and so vanishes, leaving only the 30°segments remaining. In our case, segments ''D2'', ''F1'' and ''F2'' are 30°dislo-cations, while ''D1'' is of approximately 60°charac-ter (since it has terminated its motion upon arrival at the n -/p + interface, where the electron-hole recombination goes to zero).…”

Nitrogen doping and multiplicity of stacking faults in SiC

“…However, in contrast to the present problem, where processed 4H-SiC wafers were used for the fabrication of Schottky diodes, the stacking faults in degraded PiN diodes are single-and not Role of nitrogen in the formation of stacking faults double-layered [22]. In addition, it appears that in a bipolar device, such as a PiN diode, the high density of electron-hole pairs that are generated during device operation (forward biasing), recombine non-radiatively and the resulting recombination energy contributes to the glide of partial dislocations by effectively reducing the activation enthalpy for glide [23][24][25]. This is a well-known mechanism in semiconductors, called recombination-enhanced dislocation glide (REDG), and has been discussed extensively, e.g.…”