Optical, Electrical and Lifetime Characterization of In-Grown Stacking Faults in 4H-SiC
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0911-B03-05
Optical, Electrical and Lifetime Characterization of In-Grown Stacking Faults in 4H-SiC Joshua David Caldwell, Paul B Klein, Orest J Glembocki, Robert E Stahlbush, Kendrick X Liu, Karl D Hobart, and Fritz Kub Electronic Science and Technology Division, Naval Research Laboratory, 4555 Overlook Ave, S.W., Washington, DC, 20375
ABSTRACT Here we present optical beam induced current, electroluminescence, time resolved photoluminescence and current-voltage measurements on several 4H-SiC PiN diodes containing in-grown stacking faults (IGSFs). These defects were observed to act as either current shorts, creating a direct electrical contact between the p+ and n+ layers, or as a current barrier. Carrier lifetime measurements verify that the change in behavior is indeed associated with changes in the conductivity of the material in the vicinity of the defect and not due to local changes in the carrier lifetime. The IGSFs discussed here appear to differ from those previously discussed in the literature and may constitute a new, multi-layered IGSF. INTRODUCTION In-grown stacking faults (IGSF) within 4H-SiC epilayers and diodes have recently come under increased scrutiny. Currently, three different types have been identified; a triple SF,[1] the basal plane stacking fault associated with the carrot defect [2] and the 8H-SiC planar inclusion.[3, 4] However, electrical characterization has been limited to IV [4] and Ballistic Electron Emission Microscopy [5]. Here we contrast two varieties of IGSFs via optical and electrical characterization in 4H-SiC PiN diodes and present data supporting the possible identification of a fourth type, consisting of multiple stacked layers of planar defects and/or dislocations. This new variety provides an electrical short between the p+ top layer and the substrate, altering the forward voltage characteristics and causing dramatic increases in leakage currents. EXPERIMENT The samples utilized for this study were grown on n+ 4H-SiC substrates (>300 µm thick), cut 8° off axis. A 100 µm thick, n-type epitaxial layer was grown with nominal doping levels in the mid 1014 cm-3 range and a thin (2-3 µm) p+ epitaxial layer was then grown on top. Ohmic contacts were deposited on the front and back-side, with a gridded contact structure on the frontside being created using photolithography. Further discussion of a device fabrication similar to what was used here is available in the literature [6]. Measurements were made on 9 separate diodes, D29L, D46R, D3 and D4 with IGSFs and comparison diodes D29R, D46L, D1 and D2 without IGSFs, but from the same wafer and proximity, respectively. Furthermore, diode DC3, which also contained an IGSF, will be discussed. The diodes were taken from four wafers, with samples varying in size from double diode dies to a full 3” wafer patterned with a series of diode contacts. The diodes themselves varied from 1.2 to 2.4 mm2 in size.
Electroluminescence (EL) images were collected using a sensitive, liquid nitrogen cooled charge-couple device (CCD) camera, mounted o
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