Formation mechanism of horizontal-half-loop arrays and stacking fault expansion behavior in thick SiC epitaxial layers

Abstract

The formation mechanism of half-loop arrays (HLAs) that form parallel (horizontal) to the step-flow direction in 120 μm thick 4H-silicon carbide (SiC) epitaxial layers was investigated using ultraviolet photoluminescence (UVPL) imaging and x-ray topography (XRT). The horizontal-HLAs are generated by the multiplication and glide of basal plane dislocation (BPD) loops that are created within the epitaxial layer. The BPD loops were initiated after ∼40–50 μm of growth from a small BPD segment, which glides toward the surface as well as the substrate interface. BPD multiplication occurs and several loops are generated. Some of these loops are terminated by the growth front and create HLAs due to the 4° offcut of the wafer. XRT images show that successive BPD loops interact with previously generated HLA segments. Successive loops also interact with the moving growth front and create new HLAs that are spatially displaced from the previous HLA segments. These appear as a string of horizontal-HLAs in the UVPL images. The expansion of stacking faults (SFs) from these horizontal-HLAs was investigated, and we show that they all lie on the same basal plane. The complex defect structure is created in the epitaxial layer from a single BPD loop but extends over a large (∼5 × 0.5 cm2) region of the SiC wafer during epitaxial growth. The high density of HLAs and BPDs would generate several SFs upon device operation leading to severe device degradation.

Nanoscale Infrared Spectroscopic Characterization of Extended Defects in 4H-Silicon Carbide

“…Despite the commercialization of unipolar 4H-SiC devices in the early 2000s, defects remained a challenge for bipolar and higher voltage (6.5 kV+) devices. 4,5 Other promising WBG semiconductors such as GaN and β-Ga 2 O 3 6−10 also face issues such as reduced breakdown voltage and increased leakage current due to extended defects. 6,7 Examples of extended defects include micropipes, 11 threading dislocations (TD), 12 basal plane dislocations (BPDs), 13 ingrown stacking faults (IGSF), 14 polytype inclusions, 15 and recombination-induced stacking faults (RISF).…”

“…Similar formation energies of its many polytypes hampered development via challenges in crystal growth and defect formation. Despite the commercialization of unipolar 4H-SiC devices in the early 2000s, defects remained a challenge for bipolar and higher voltage (6.5 kV+) devices. , Other promising WBG semiconductors such as GaN and β-Ga 2 O 3 − also face issues such as reduced breakdown voltage and increased leakage current due to extended defects. , Examples of extended defects include micropipes, threading dislocations (TD), basal plane dislocations (BPDs), in-grown stacking faults (IGSF), polytype inclusions, and recombination-induced stacking faults (RISF) . The impact of these defects on device performance depends on the combination of defect structure, material system, and device type.…”

Formation of basal plane dislocations by stress near epilayer/substrate interface of large-diameter SiC wafers with thick epitaxial layers

“…However, in epitaxial wafers with thick epilayers, the effect of the lattice mismatch extends to the substrate side, generating a considerable stress inside the substrate. Mahadik et al 21 recently reported the formation of BPD loops in a 120 μm thick 4H-SiC epi-wafer. They observed BPDs that were generated by inclusion and propagated beyond the epi/sub interface to the interior of the substrate.…”