Extended Defects in 4H-SiC PiN Diodes
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Extended Defects in 4H-SiC PiN Diodes M. E. Twigg1*, R. E. Stahlbush1, M. Fatemi1, S. D. Arthur2, J. B. Fedison2, J. B. Tucker2, and S. Wang3 1 Electronics Science and Technology Division, Naval Research Laboratory, Washington DC, 20375 2 General Electric Corporation Research and Development Center, Niskayana, NY 3 Sterling Semiconductor, Danbury, CT ABSTRACT Using site-specific plan-view transmission electron microscopy (TEM) and lightemission imaging (LEI), we have identified SFs formed during forward biasing of 4H-SiC PiN diodes. These SFs are bounded by Shockley partial dislocations and are formed by shear strain rather than by condensation of vacancies or interstitials. Detailed analysis using TEM diffraction contrast experiments reveal SFs with leading carbon-core Shockley partial dislocations as well as with the silicon-core partial dislocations observed in plastic deformation of 4H-SiC at elevated temperatures. The leading Shockley partials are seen to relieve both tensile and compressive strain during PiN diode operation, suggesting the presence of a complex and inhomogeneous strain field in the 4H-SiC layer.
INTRODUCTION Silicon Carbide is a wide band gap semiconductor with promising applications in highpower devices. The recent development of 4H and 6H SiC substrates with dislocation densities of less than 103/cm2 bodes well for the development of electrical devices based on SiC thin films grown homoepitaxially by chemical vapor deposition (CVD). However, recent studies of 4HSiC PiN diodes have revealed that extended defects grow during device operation, causing a degradation of the forward-biased operation [1,2]. A number of authors have suggested that the extended defects seen to form in 4H-SiC PiN diodes under forward bias operation are stacking faults (SFs) [1-5]. Cross-sectional transmission electron microscopy (XTEM) observations indicate that these planar defects occur in 4H-SiC are Shockley faults [3]. Light Emission Imaging (LEI) reveals that the degradation of 4H-SiC PiN diodes under forward voltage operation is due to the lateral migration of the SFs, as well as their migration to the surface of the active device region [4,5]. Our objective is to use site-specific plan-view transmission electron microscopy (PVTEM) to directly observe diodes that have been biased at ambient-temperature during LEI observation, and identify the extended defects.
EXPERIMENTAL DETAILS The SFs were introduced into the 4H-SiC PiN diode presented here by electrically stressing under forward bias at 160 A/cm2 for an accumulated time of 50 min. During the stressing, the junction temperature was kept below 100oC by using a low duty cycle, and SF growth was monitored by LEI. The details of the diode fabrication have been previously
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reported [5]. The wedge-shaped plan-view specimens observed in this study have been prepared by angle-lapping using a tripod angle polishing tool, and are able to sample a large area of each 4H-SiC PiN diode. The surface of the sample was smoothed and the device metallization
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