Multiplication of Basal Plane Dislocations via Interaction with c-Axis Threading Dislocations in 4H-SiC
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0911-B09-04
Multiplication of Basal Plane Dislocations via Interaction with c-Axis Threading Dislocations in 4H-SiC Yi Chen1, Govindhan Dhanaraj1, Michael Dudley1, Hui Zhang2, Ronghui Ma3, Yevgeniy Shishkin4, and Stephen E Saddow4 1 Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794-2275 2 Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY, 117942300 3 Department of Mechanical Engineering, University of Maryland at Baltimore County, Baltimore, MD, 21250 4 Department of Electrical Engineering, University of South Florida, Tampa, FL, 33620
ABSTRACT Silicon carbide (SiC) substrates with chemical vapor deposition (CVD) grown epilayers have been characterized by synchrotron white beam X-ray topography (SWBXT). Large numbers of circular basal plane dislocation loops (BPDs) were observed in the substrate which were anchored by threading screw dislocations (SDs). Threading edge dislocations (TEDs) are not observed to play an important role in the multiplication of BPDs. A SD-assisted “conservative climb” model is proposed to explain the multiplication of BPDs during growth and/or post-growth processes. BPDs are shown to multiply on adjacent parallel basal planes via single SD-assisted as well as opposite sign SD-pair-assisted “conservative climb”. INTRODUCTION Silicon carbide (SiC), a wide band-gap semiconductor, is steadily growing and replacing conventional silicon in certain critical applications. Its unique combination of properties including high thermal conductivity, saturated electron drift velocity and breakdown field make it suitable for high temperature, high power and high frequency device applications. For example, SiC-based electronic devices and sensors are used in automotive and modern aircraft engines to monitor emissions. Hollow-core superscrew dislocations (micropipes, or MPs) have been found to be “device-killing” defects in SiC [1] and several mechanisms have been proposed to interpret the formation of MPs (see for example [2]). Furthermore, closed-core screw dislocations with Burgers vector 1c/2c have been reported to reduce the breakdown voltage by 535% [3]. Both hollow and closed-core screw dislocations are growth dislocations, i.e. they are not produced by the usual dislocation multiplication mechanisms but rather are replicated on the moving crystal growth interface which is modified by their intersection [4]. Expansion of I2 type stacking faults bounded by Shockley partial dislocations (PDs) dissociated from BPDs results in an increase of voltage drop under forward bias in 4H-SiC p-n diodes [5]. This may be related to the thermodynamic instability of the polytype. Recently, high densities of threading edge dislocations (TEDs) were also found to affect breakdown voltage [6]. Although SiC epilayers with low densities of BPDs have been grown at temperatures around 1500oC by chemical vapor deposition (CVD) [7-9], comprehensive understanding of the formation and multiplication mechanisms of BPDs so as to be able to provide feedbac
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