Effect of Seed Off-Axis Angles on Distribution of Basal Plane Dislocations in Top-Seeded Solution Growth of SiC Crystals

doi:10.16553/j.cnki.issn1000-985x.xb2026.0021

Abstract

Abstract: Basal plane dislocations （BPDs） are critical defects that severely degrade the quality of 4H-silicon carbide （SiC） crystal and the performance of 4H-SiC based devices. The top-seeded solution growth （TSSG） method is promising for high-quality SiC crystals with its near-thermodynamic equilibrium conditions. However，the distribution of thermal stress and BPDs is not fully understood in the TSSG growth of 4H-SiC crystals. Both on-axis and off-axis seeds are widely used in the industrial TSSG processes. To investigate the effect of seed off-axis angle （θ_off） on thermal stress and BPDs in 4H-SiC crystals grown by the TSSG method，a multi-physics coupled model was developed in this study by integrating global heat transfer，three-dimensional thermoelastic stress analysis，and the Alexander-Haasen dislocation evolution model. The resolved shear stress （RSS） and BPDs density distributions in 4H-SiC crystals grown at off-axis angles of 0°，4°，60°，and 90° were systematically simulated and analyzed. The results show that the seed off-axis angle critically affects the RSS distribution at the growth interface. Under on-axis （θ_off=0°） growth，the RSS exhibits a highly symmetric，low-stress state，with stress near the center approaching zero and only minor perturbations at the edge. At the θ_off is 4°，the RSS shows axisymmetric regional patterns. At the θ_off is 60°，the RSS transitions to a fourfold symmetric distribution with alternating tensile and compressive stresses，and the stress amplitude increases by an order of magnitude compared to that at θ_off ≤4°. At the θ_off is 90°，the RSS becomes fully fourfold symmetric distribution. Under all conditions，the maximum RSS on the growth surface is lower than that on the seed back surface，and high-stress regions consistently concentrate at the crystal periphery. The density and distribution of BPDs closely correlate with RSS. Under on-axis growth，BPDs exhibit a sixfold symmetric distribution. As the θ_off increases，the BPDs distribution gradually transitions to fourfold symmetric distribution，and the overall BPDs density increases significantly. At the θ_off are 60° and 90°，the maximum BPDs density reaches approximately 10⁵ cm^-2，which is two orders of magnitude higher than that at 4° （approximately 10³ cm^-2）. This substantial increase indicates that large θ_off promote BPDs multiplication and are detrimental to high-quality crystal growth. In addition，the BPDs density is consistently higher on the seed back surface than on the growth surface，and high-BPDs regions coincide with high-RSS regions at the crystal periphery. This study elucidates the correlation among the seed off-axis angle，thermal stress field，and BPDs distribution in 4H-SiC crystals grown by the TSSG method. The findings demonstrate that using a seed with a small off-axis angle （≤4°） effectively suppresses BPD generation，thereby facilitating the growth of high-quality 4H-SiC single crystals. These results provide theoretical guidance for optimizing the TSSG process to achieve low defect density and high crystalline perfection.

Key words: top-seeded solution growth; SiC crystal; numerical simulation; off-axis angle; shear stress; basal plane dislocation

CLC Number:

O782

LUAN Sen, QI Xiaofang, MA Wencheng, XU Yongkuan. Effect of Seed Off-Axis Angles on Distribution of Basal Plane Dislocations in Top-Seeded Solution Growth of SiC Crystals[J]. Journal of Synthetic Crystals, 2026, 55(6): 886-897.

Figures/Tables 11

Fig.1 Schematic diagram of growth furnace structure for SiC crystal by TSSG method

Table 1 Material physical property parameters in numerical simulation

Material	Property	Value	Unit
Si-40% （mole fraction） Cr	Density，ρ	5 199-0.552T	kg/m³
	Specific heat capacity，C_p	1 196	J/（kg∙K）
	Thermal conductivity，λ	-68.28+5.4×10^-2T	W/（m∙K）
	Dynamic viscosity，μ	1.266×10^-3exp（1 982/T）	Pa∙s
Graphite	Density，ρ	1 950	kg/m³
	Specific heat capacity，C_p	710	J/（kg∙K）
	Thermal conductivity，λ	150	W/（m∙K）
Graphite felt	Density，ρ	120	kg/m³
	Specific heat capacity，C_p	200	J/（kg∙K）
	Thermal conductivity，λ	0.336	W/（m∙K）
SiC	Density，ρ	3 215	kg/m³
	Specific heat capacity，C_p	1 463.9	J/（kg∙K）
	Thermal conductivity，λ	6.11×10 000/（T-115）	W/（m∙K）
Argon	Specific heat capacity，C_p	520.33	J/（kg∙K）
Argon	Thermal conductivity，λ	0.07	W/（m∙K）

Fig.2 Crystal growth simulation model. （a） Two-dimensional temperature distribution of crystal；（b） temperature distribution in three-dimensional model after importing two-dimensional temperature data；（c） three-dimensional mesh and boundary conditions for thermal stress simulation

Fig.3 Schematic diagram of slip systems in basal plane of hexagonal crystal system

Table 2 Parameters for A-H model

Property	Value and unit
Burgers vector，b	3.073×10^-10 m
Stress exponential factor，m	2.8
Activation enthalpy，Q	3.3 eV at T>1 000 ℃ 2.6 eV at T<1 000 ℃
Dislocation velocity，v	m/s
Multiplication constant，K	7×10^-5
BPDs density in $a k$ direction， $N m (a k)$	m^-2
Boltzmann constant， $k B$	8.615×10^-5 eV/K

Table 2 Parameters for A-H model

Property	Value and unit
Burgers vector，b	3.073×10^-10 m
Stress exponential factor，m	2.8
Activation enthalpy，Q	3.3 eV at T>1 000 ℃ 2.6 eV at T<1 000 ℃
Dislocation velocity，v	m/s
Multiplication constant，K	7×10^-5
BPDs density in $a k$ direction， $N m (a k)$	m^-2
Boltzmann constant， $k B$	8.615×10^-5 eV/K

Fig.4 Distribution of resolved shear stress （τRSS） in different slip directions of crystals under different off-axis angles

Fig.5 Maximum shear stress in crystals under different off-axis angles （a） and resolved shear stress in different slip directions （b）

Fig.6 Distribution of total shear stress in crystals under different off-axis angels. （a） Back surface of seed |τtotal|；（b） growth surface |τtotal|

Fig.7 Distribution of BPDs density in 4H-SiC crystals under different off-axis angles. （a） 0°；（b） 4°；（c） 60°；（d） 90°

Fig.8 Distribution of BPDs density under different off-axis angles for different cross-sections. （a） Back surface of seed；（b） growth surface

Fig.9 Distribution of maximum values of BPDs density along various cross-sections under different off-axis angles

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