J. Q. Liu

Structure of recombination-induced stacking faults in high-voltage SiC p–n junctions

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.

Structural instability of 4H–SiC polytype induced by n-type doping

Spontaneous formation of stacking faults in heavily nitrogen-doped 4H-polytype silicon carbide crystals have been observed by transmission electron microscopy (TEM). Faults were present in as-grown boules and additional faults were generated by annealing in argon at 1150 °C. All faults had identical structure consisting of six layers stacked in a cubic sequence as determined by high-resolution TEM, and were interpreted as a result of two Shockley partial dislocations gliding on two neighboring basal planes of SiC. It is argued that the energy of faulted 4H silicon carbide is lower than the energy of perfect heavily doped (n>1×1019 cm−3) crystal at typical processing temperatures, thus providing a driving force for transformation.

Recombination-enhanced defect motion in forward-biased 4H–SiC p-n diodes

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 a...

Nucleation of threading dislocations in sublimation grown silicon carbide

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.

Dislocation loops formed during the degradation of forward-biased 4H–SiC p-n junctions

Abstract The partial dislocations that border triangle or parallelogram-shaped stacking faults formed during the degradation of p-n diodes fabricated on 4H–SiC wafers were determined by transmission X-ray topography to be dislocation loops of Burgers vector 1/3〈10 1 0〉, the Shockley partial type, consistent with previously reported TEM results. Some were separated from axial screw dislocations also present in the sample, indicating that the axial dislocations were not involved in the loops’ nucleation; while others were seen to have interacted during their growth with the axial screw dislocations, distorting their shapes from those of ideal parallelograms.

Pseudomorphic SiC alloys formed by Ge ion implantation

Pseudomorphic-strained layers containing from 0.07–1.25atomic% Ge were formed by ion implantation at 1000°C into 4H-SiC substrates. X-ray diffraction revealed high crystalline quality and coherent interfaces for strains up to 1.4%. Infrared reflectivity indicated a phonon mode at 948cm−1, attributed to Ge implantation disorder. Annealing above 1250°C caused the disappearance of the 948cm−1 disorder mode, and the strengthening of the phonon mode at 848cm−1, associated with the 4H stacking sequence. Structural measurements of the annealed samples revealed thermally stable, coherently strained layers of the 4H polytype, without precipitation, suggesting an isoelectronic Ge alloy compatible with SiC for heterostructure strained layer engineering.

Stacking fault formation in highly doped 4H-SiC epilayers during annealing

Spontaneous stacking fault formation during annealing in n(+) 4H-SiC epilayers deposited on the n(-) 4H-SiC substrates has been analyzed by conventional and high-resolution transmission electron mi ...

Surface-damage-induced threading dislocations in 6H-SiC layers grown by physical vapor transport

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 [0001] and Burgers vector of a/3 . The edge dislocations are arranged in form of cellular structures with cell walls aligned preferentially along <1-100) 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 2 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 μm. The formation of threading dislocations is associated with the subsurface damages caused by plastic deformation during the mechanical polishing process.