Nucleation mechanism of dislocation half-loop arrays in 4H-silicon carbide homoepitaxial layers

Abstract

A model is presented for the formation mechanism of dislocation half-loop arrays formed during the homoepitaxial growth of 4H-SiC. The reorientation during glide of originally screw oriented threading segments of basal plane dislocation (BPD) renders them susceptible to conversion into sessile threading edge dislocations (TEDs), which subsequently pin the motion of the BPD. Continued glide during further growth enables parts of the mobile BPD to escape through the surface leaving arrays of half loops comprising two TEDs and a short BPD segment with significant edge component. The faulting behavior of the arrays under UV excitation is consistent with this model.

X-ray Topography Studies of Relaxation during the Homo-Epitaxy of 4H-SiC

“…1 (a) reveals the presence of pairs of additional linear features which are slightly inclined to the ID segments. The Burgers vector associated with these features is also 1/3 [11][12][13][14][15][16][17][18][19][20]. These features are also clearly visible in Fig.…”

“…These configurations comprise two straight, screw-oriented BPD segments (with Burgers vector along the offcut direction, i.e. 1/3 [11][12][13][14][15][16][17][18][19][20], as determined by their invisibility on the [1-100] reflection, not shown here) in the substrate, connected to two ID segments, which in turn are connected to two mobile segments on the basal plane of the epilayer. The lower ends of the straight, screw oriented segments in the substrate are invariably connected to complex BPD nodes that apparently have provided pinning points.…”

“…Conversion rates of up to 99% have been reported [8,9] with only the remaining 1% which are usually in screw orientation, with Burgers vector along the offcut direction, being available for replication. While such screw oriented BPD segments present in the drift layer of devices can themselves lead to Shockley fault expansion, they can become even more harmful if strain relaxation occurs whereby they are forced to glide in the epilayer leading to the simultaneous production of IDs [2,10,11] and arrays of dislocation half loops known as HLAs [3,[11][12][13]. Sasaki et al recently demonstrated that the mismatch stress at the CVD growth temperature, in similarly doped systems as those studied here, is large enough to lead to such relaxation [14].…”

“…Within the HLAs, each half loop comprises of a short BPD segment connected to the surface by two threading edge dislocation (TED) segments. The short BPD segments provide multiple sites for the expansion of the Shockley faults that cause forward voltage drop thus further exacerbating the problem [12]. It is therefore of great interest to understand the sources for these IDs and HLAs.…”

Electron-beam-induced current and cathodoluminescence study of dislocation arrays in 4H-SiC homoepitaxial layers

“…10 The recombination activities of dislocations in 4H-SiC homoepitaxial layers were reported to be stronger in the order of BPDϾ TSDϾ TED. 11 Recently, it has shown that one kind of TEDs, dislocation arrays ͑DAs͒, can also be dissociated to form SFs, [12][13][14] although they have the lowest recombination activity. Thus, extensive studies are needed to clarify their dissociation behavior.…”