High-resolution x-ray topography of dislocations in 4H-SiC epilayers
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William M. Vetter and Michael Dudley State University of New York, Department of Materials Science and Engineering, Stony Brook, New York 11794-2275 (Received 24 August 2006; accepted 5 January 2007)
Synchrotron x-ray topography with a high-resolution setup using 112¯8 reflection was carried out on 4H-SiC epilayers. Four different shapes of threading-edge dislocation according to Burgers vector direction were observed. The four types of threading-edge dislocation images were calculated by computer simulation, and the experimental results correlated well with the simulation results. The detailed topographic features generated by plural screw dislocations and basal plane dislocations were also investigated.
I. INTRODUCTION
SiC has excellent material properties, including a superior breakdown electric field, high thermal conductivity, and wide energy band gap. SiC devices are thus expected to be low-loss, high-voltage, and hightemperature resistive devices. Recently, some excellent performance of SiC devices has been reported.1 While SiC substrates and epitaxial layers (epilayers) still contain many crystal defects, large devices have yet to demonstrate good performance. Thus, it is important to understand the precise properties of crystal defects and dislocations and to reduce harmful defects and dislocations. Micropipes, screw dislocations, threading edge dislocations (TEDs), and basal plane dislocations (BPDs) are known as dislocations in SiC substrates and epilayers and may affect device performance. The micropipes produce lower reverse blocking voltages of devices.2 The BPDs in an epilayer introduce stacking faults when bipolar devices operate in a forward voltage bias (on-state) with forward current.3 For these reasons great effort has been dedicated to reducing the crystal defects in substrates and epilayers. Micropipes were dramatically reduced in commercial wafers in this decade,4 and micropipes closed in the epitaxial layer during chemical vapor deposition (CVD) growth by dissociation into several screw dislo-
cations.5 Recently, repeating a-face (RAF) growth has dramatically reduced dislocations.6 X-ray topography is a powerful tool used to observe crystal defects and dislocations in SiC. It is a nondestructive evaluation method, and there is no difference in this observation for Si-face and C-face samples. X-ray topography also provides in-depth information on dislocations in a sample. In a homoepilayer grown on a 4H-SiC wafer with an 8° surface off-cut, three types of dislocation are included: threading screw dislocations, TEDs, and BPDs propagating into an epitaxial layer at 8° inclinations. These types showed different topographic images when monochromatic synchrotron x-ray topography was performed by grazing-incidence reflection geometry using 112¯8 reflection.7 On the other hand, the fine structures of the dislocation images were proposed using the ray-tracing method of computer simulation.8 However, experimental images of dislocations were not fully matched to the fine structure of simulation ima
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