The structure of stacking faults formed in forward-biased 4H- and 6H-SiC p–n− diodes was determined using conventional and high-resolution transmission electron microscopy. Typical fault densities were between 103 and 104 cm−1. All observed faults were isolated single-layer Shockley faults bound by partial dislocations with Burgers vector of a/3〈1–100〉-type.

The generation and evolution of defects in 4H–SiC p-n junctions due to carrier injection under forward bias have been investigated by synchrotron white beam x-ray topography, electroluminescence imaging, and KOH etching. The defects are Shockley stacking faults with rhombic or triangular shapes bound by partial dislocation loops with dislocation lines along Peierls valleys (〈11-20〉) or along the intersection of the basal plane containing the fault and diode surface. The Burgers vector of all bounding partials was of 1/3〈10-10〉-type. Among six possible types of partial dislocations with these properties, only two were observed in the volume of the epitaxial structure. One was tentatively identified as 30° carbon-core [C(g) 30°] and second as 30° silicon-core [Si(g) 30°] partial dislocation. Only one of them [proposed to be the Si(g) 30° partial] have been observed to move and emit light under forward bias. The other type of bounding dislocation [C(g) 30°] remained stationary during current injection. Low angle grain boundaries have been observed to act as one of a number of possible nucleation sites of stacking faults.

The structural defects in sublimation-grown silicon carbide layers have been investigated by transmission electron microscopy, atomic force microscopy, x-ray topography, and KOH etching. Nucleation of two-dimensional islands on damage free surfaces of high quality Lely seeds led to formation of stacking faults at the initial stages of growth. The location and number of stacking faults correlates with threading dislocation density. Also, the growth rate is shown to have a pronounced effect on the threading dislocation densities. Elementary screw dislocation density has been observed to increase from 20 cm−2 to 4×103 cm−2 for growth rates increasing from 0.02 to 1.5 mm/h. Growth on seeds miscut 5° off the c axis resulted in screw dislocation densities almost two orders of magnitude lower than on axis growth. The results are interpreted as due to SiC stacking disorder at the initial stages of growth.

Several characteristic features of surface-damage-related threading dislocations in SiC epitaxial layers have been investigated by transmission electron microscopy. Most of the observed threading dislocations are perfect-edge type with line direction along ͓0001͔ and Burgers vector of a/3͗11-20͘. The edge dislocations are arranged in form of cellular structures with cell walls aligned preferentially along ͗1-100͘ directions. Some small isolated cells were also observed in the areas of lower dislocation density. The density of elementary screw dislocations in the overgrowth was approximately 10 5 cm Ϫ2 and is about two orders of magnitude lower than the edge dislocation density. The screw dislocations appeared in pairs with the opposite sign of Burgers vectors separated by about 0.3 m. The formation of threading dislocations is associated with the subsurface damages caused by plastic deformation during the mechanical polishing process.

Silicon carbide (SiC) is a wide bandgap semiconductor with outstanding properties, such as high thermal conductivity, high electric breakdown voltage, and high carrier saturation velocity, making it an attractive candidate for potential applications in high-power, high-temperature and highfrequency electronic devices. As an IV-IV compound semiconductor, the crystal structure of SiC can be described in terms of an assembly of corner-sharing tetrahedra. In each tetrahedron, an atom of carbon (or silicon) at the centroid is bonded to four atoms of silicon (or carbon) at the corners. SiC exhibits a number of structural variants called polytypes. The most common polytypes of SiC are 6H, 4H, 3C and 15R (Ramsdell's notation) with C, H, and R representing cubic, hexagonal and rhombohedral structure, respectively, and the numbers denoting the periodicity of tetrahedral along c-axis of the crystal. The bandgap of SiC increases in proportion to its "hexagonality" (from 2.2 eV for 3C to 3.2 eV for 2H). In the past two decades, the technology for the SiC crystal growth has been improved, including bulk growth, epitaxial growth and heteroepitaxial growth. The investigations of defects in the crystals and electronic devices are indeed of fundamental importance, since the presence of defects affects the crystal physical properties and performance of devices.A recently reported degradation phenomenon, that occurred in 4H-and 6H-SiC diodes during the forward-bias operation, was proposed to be associated with the presence of extended defects in the epitaxial layers. [1][2][3] This paper presents one example of extended defect characterizations in SiC by transmission electron microscopy (TEM). 3C-SiC films were deposited on device-sized mesas fabricated on hexagonal 4H-SiC on-axis substrates.[4] Some 3C-SiC heterofilms are completely free of doubleposition-boundaries (DPB's) and stacking faults (SF's). However, isolated stacking faults were revealed by thermal oxidation on some nearly ideal mesas. [4] We are attempting to determine the detailed microstructure of an isolated fault at its nucleation site by high-resolution TEM. In spite of the small size (0.1 × 0.1 mm) of the mesa, the cross-sectional TEM sample was made using a "sandwich" method. Figure 1 illustrates the sample preparation procedures. A conventional TEM image of the fault is shown in Figure 2. High-resolution TEM examination is ongoing.