Mechanism of Replicating Polytype of 4H-SiC by Solution Growth on

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Mechanism of Replicating Polytype of 4HSiC by Solution Growth on Concave Surface Hironori Daikoku, Sakiko Kawanishi, and Takeshi Yoshikawa Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00032 • Publication Date (Web): 25 May 2018 Downloaded from http://pubs.acs.org on May 25, 2018

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Crystal Growth & Design

Mechanism of Replicating 4H-SiC Polytype during Solution Growth on Concave Surface Hironori Daikoku*1, Sakiko Kawanishi2, Takeshi Yoshikawa1

1

Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo

153-8505, Japan 2

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1,

Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan *E-mail: [email protected] KEYWORDS: Silicon carbide, top-seeded solution growth, polytype, concave surface

Abstract To determine the mechanism of 4H-SiC replication during solution growth on a concave surface, SiC growth on 2-inch-diameter 4H-SiC (0001ത) seed and on 0.5-inch square seeds of different planes was carried out at 2273 K using Si–40mol%Cr-based solvent with and without Al addition. Grown crystal that replicated 4H-SiC possessed (11ത02ത) facets at the periphery of the growth interface, with its growth tips located at both edges of the facet. Al addition to the solvent enlarged such facets on the growth interface and increased the probability of 4H-SiC replication. Furthermore, Al addition to the solvent improved the stability of crystal grown on (11ത02ത) seed, as evaluated from surface roughness analysis. According to the surface stability, we proposed a mechanism for 4H-SiC replication and the effect of Al addition into the solvent during solution growth on a concave surface. Introduction Silicon carbide (SiC) is a promising material for applications in high-voltage power devices due to its high electric field strength, high thermal conductivity, and high electron mobility [1, 2]. SiC has a number of polytypes with different stacking sequences of Si–C bilayers along the c-axis; those of 4H-, 6H-, 3C-, 1

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and 15R-SiC have high generation frequency. Of these, 4H-SiC is suitable for high-power and hightemperature electronics because of its superior properties attributed to its wide bandgap. To date, mass production of 4H-SiC bulk crystals used for power devices has been carried out using the physical vapor transport (PVT) method; however, PVT wafers have not yet been commercially adopted because the cost of SiC is much higher than that of Si in conventional devices. In addition, currently available SiC crystals contain a variety of crystalline defects that significantly reduce material and device yields and consequently increase the production cost. Low-cost, high-quality wafers are needed to achieve widespread adoption of SiC power devices. Solution growth has attracted significant attention with regard to its ability to generate high-quality SiC wafers, because the growth proceeds close to thermal equilibrium [3]. A decrease in dislocation density of 4H-SiC crystals generated by solution growth has recently been reported [4, 5]. A wafer with low dislocation density can be useful for bipolar devices because defects such as dislocations are detrimental to such devices [6]. The growth rate in solution growth techniques has been greatly improved by adding transition metals to Si-based solvents to increase the carbon solubility [7, 8, 9]; however, two issues still need to be solved to achieve practical application of solution growth. When the growth rate is increased, surface instability occurs and causes solvent inclusions in the grown crystal. Such inclusions in wafers may affect the properties of epilayers and contaminate the chemical vapor deposition process. One of the authors proposed carrying out solution growth on a concave surface (the so-called SGCS method) with a silicon (Si)–chromium (Cr)-based melt to improve the surface instability [10]. Application of convection of the solution in the opposite direction to that of step flow during solution growth suppresses step bunching, resulting in a smooth surface without solvent inclusions; however, the surface instability issue remains when further rapid growth and larger diameter crystal growth are attempted. Control of the replication of 4H-SiC from (0001ത) seed crystal is also a significant issue. Generally, spiral growth at a threading screw dislocation (TSD) is well known to allow replication of this polytype, because the spiral growth steps comprise its particular stacking sequence. Regarding the PVT process, 2


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carbon (C)-enriched growth conditions are beneficial to the growth of polytypes with higher hexagonality, such as 4H-SiC [11]. Addition of aluminum (Al) to the growth field leads to preferential growth of 6HSiC, rather than 4H-SiC, on (0001) seed in PVT growth. In the case of solution growth, we reported that Al addition to the Si-Cr solvent did not change the carbon solubility [12]. Mitani et al. [13] reported that Al addition to the solvent stabilized interface morphology and replication of the 4H-SiC polytype under Al–N co-doping conditions. Hence, suitable conditions for PVT growth are not always applicable to solution growth. Knowledge of the mechanism and suitable conditions to control the 4H-SiC polytype are indispensable to the solution growth process. In this study, we investigated the replication conditions of 4H-SiC and the effect of Al addition to the solvent during the SGCS process. The growth of 2-inch-diameter SiC crystals by SGCS from Si– 40mol%Cr-based solvent was performed at 2273 K and the growth plane was examined for both 4H-SiCreplicated and 6H-SiC-converted crystals. Growth of SiC crystal from Al-added solvents was then conducted to determine the probability of 4H-SiC replication. Solution growth on seeds of different planes was carried out with and without Al addition to the solvent, and the interface stability and Al incorporation into the grown crystals were examined. Finally, we proposed a mechanism for 4H-SiC replication and the effect of Al addition to the solvent during the SGCS process.

Experimental Methods 1. Solution Growth on Concave Surface with 2-Inch-Diameter Seed Solution growth was performed in a top-seeded solution growth (TSSG) furnace in helium ambient atmosphere, as shown in Fig. 1 [14]. Two-inch wafers of n-type 4H-SiC (0001ത) were used as the seed crystals. A Si–40mol%Cr–based mixture with or without the addition of Al was charged in a high-purity graphite crucible (inner diameter: 100 mm) to achieve a melt height of 35 mm. After adjusting the pressure of the chamber to 40 kPa, the graphite crucible was heated by induction heating (5 kHz) until the temperature at the solution surface reached 2273 K. The temperature gradient from the solution surface to a depth of 10 mm was about 20 K/cm. The accelerated crucible rotation 3



technique was applied to enhance mixing in the melt [14]. The rotation rates of the seed and crucible were controlled at 10 rpm and 5 rpm, respectively. The meniscus-forming technique was applied to suppress parasitic reactions, such as polycrystalline SiC precipitation around the seed crystal. The meniscus height was controlled to 0.5 to 2 mm by pulling the seed at 0.05 to 0.2 mm/h during solution growth. Surface morphologies of the grown crystals were investigated using Nomarski microscope (Nikon, LV100) and laser microscope (KEYENCE, VK-X200). To investigate the distribution of dislocation density on the as-grown surfaces, molten KOH etching was conducted at 773 K [15]. The polytype was evaluated across the entire interface at intervals of 0.25 mm by Raman scattering (PHOTON DESIGN). In addition, carrier concentration and conduction type were estimated from deviation of the Raman shift for longitudinal optical (LO) phonons from 947 cm−1 due to plasmon coupling [16]. Impurity concentrations in the grown crystal were analyzed by secondary-ion mass spectroscopy (SIMS型番). The resistivity of the grown crystals was evaluated by eddy-current measurement (NAPSON, EC-80P). Insert Fig. 1 here.

2. Solution Growth on Seeds of Specific Planes Using the same equipment as described in Section 1, 0.5-inch round or square crystals of n-type 4Hഥ ) (m = 0, 1, 2, 3, 4) planes were used as seeds. Si–40mol%Cr-based SiC with (0001), (0001ത), and (11ത0m solvent, with and without addition of Al, was melted in the graphite crucible. The height of the solution was about 30 mm. Surface roughness of the grown crystals was measured by laser microscope and their Al concentrations were determined by SIMS.

Results and Discussion 1. Relationship between Polytype and Crystal Shape Obtained by Solution Growth on Concave Surface using Si–Cr-based Solvent ത ) seed crystals from the Si– When SiC was grown on 2-inch-diameter n-type 4H-SiC (0001 40mol%Cr-based solvent, 60% of crystals grown in 40 runs were converted to 6H-SiC. To establish a 4


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mechanism for polytype replication from 4H-SiC seed across the entire growth interface during SGCS, the shapes of grown crystals that replicated 4H-SiC and those that fully converted to 6H-SiC were compared. Figure 2 shows a side view, plain view, and cross-section of a 4-mm-thick crystal grown for 50 h, the polytype of which was controlled to 4H-SiC across the entire growth interface. As seen in Fig. 2(a), the diameter of the grown crystal increased from that of a round-shaped seed. The side surface was composed of six (11ത0m) facets and curved surfaces. The periphery of the grown interface consisted of six segments ത 0} plane, shown in and curves corresponding to the side surfaces. In the cross-section parallel to the {112 Fig. 2(c), the growth interface was mostly concave and a region of 2 mm width from the periphery was an ത 0m ഥ ) facets were observed in Fig. 2(b) almost flat (0001ത) plane. Along the segments at the periphery, (11 ത ) plane on the growth interface. The angle between the between the side (11ത0m) facets and the (0001 ത ) facets at the ഥ ) and (0001ത) planes was estimated to be 63° in Fig. 2(c), so the formation of (11ത02 (11ത0m periphery was identified. Such facets were not observed along the edge curve at the periphery. Insert Fig. 2 here. As shown in Fig. 2(d), Nomarski observations revealed that both edges of the (11ത02ത) facets at the periphery were characterized as growth tips. Hence, twelve growth tips from both sides of six (11ത02ത) facets existed in the grown crystal. Step flow growth was directed from the tip along the periphery and a circular (0001ത) plane formed just inside the periphery. The inner concave-shaped region was covered by the step flow structure. The terrace width in the structure ranged from 1 µm to 10 µm. Two-dimensional nucleation and spiral hillocks were not observed on the concave-shaped region. Steps with high density contributed to suppressing two-dimensional nucleation and enhancing solute adsorption. Accordingly, it was determined that the growth tip was only located at the periphery and stacking information for the 4HSiC structure was transferred from the growth tip to the entire interface through the step flow growth. Figure 3 shows a side view, plain view, and cross-section of a 2-mm-thick crystal, the polytype of which was converted from a 4H-SiC seed to 6H-SiC at the initial stage of growth. The side surface was ഥ } facets and curved surfaces and the middle part of the grown interface was composed of six {11ത0m covered by the step flow structure, both of which were comparable with the results for 4H-SiC replication 5



ത ) facets were not formed at the periphery of the growth interface on shown in Fig. 2. In contrast, (11ത02 ത ) facet formation at the periphery contributed to replication of conversion to 6H-SiC, indicating that (11ത02 the 4H-SiC layer. It is well known that spiral growth at a TSD assists replication of this polytype due to its generation and supply of steps possessing the characteristic stacking sequence. To investigate whether spiral growth proceeded at the growth tip to replicate 4H-SiC, as in Fig. 2, the distribution of dislocations in the grown crystal was measured. A 4° off wafer from the basal plane was prepared from the grown crystal and subjected to molten KOH etching. Numerous etch pits were observed in the middle of the wafer, as shown in Fig. 4. The densities of TSD and threading edge dislocations (TED) were about 103 cm−2 and 105 cm−2, respectively. In contrast, the outer area of the wafer, with a width of approximately 1.8 mm, was free from hexagonal etch pits related to threading dislocations. This area corresponded to the enlarged growth region from the seed crystal, while the inner region, containing a number of threading dislocations, was located below the seed crystal. Accordingly, because threading dislocations in the seed did not affect the growth tip, an origin other than spiral growth acted to replicate 4H-SiC during SGCS. Insert Figs. 3 and 4 here.

2. Effect of Al on 2-Inch-Diameter 4H-SiC Growth Using Si–Cr-based Solvent in Solution Growth on a Concave Surface The effect of Al addition to Si–40mol%Cr-based solvent in SGCS was investigated. Figure 5 shows the SIMS results for Al and N concentrations at the central parts of crystals grown from Si–40mol%Cr-based solvent with varying Al additions. Al concentrations in the grown crystals increased with its concentration in the solvent. Under these conditions, N was not intentionally added to the solvent, but was probably incorporated from residue ofin the graphite crucible and thermal insulator. The N concentration increased as Al addition to solvent increased due to its interaction with Al in the crystal [13]. To control the growth of n-type 4H-SiC crystal with N incorporation in this furnace, maximum Al addition to the solvent was hereafter restricted to 0.5 mol%. 6


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Insert Fig. 5 here. Figure 6 shows the probability of replication of 4H-SiC and the resistivity of grown crystal of 2-inch diameter at different Al additions to the solvent, where the probability is defined as the ratio of the number of runs of crystals grown for more than 20 h with 4H-SiC replication across the entire interface of the 2inch-diameter crystal compared with the total number of runs. The probability of 4H-SiC replication without Al addition was about 50 %, as described in Section 1. The probability of 4H-SiC replication increased as the Al concentration increased, and reached 100% when Al addition exceeded 0.07 mol%. Resistivity increased with the increase of Al concentration due to charge compensation. 4H-SiC wafers with resistivities of 30 mΩ⋅cm were successfully obtained at Al concentrations of less than 0.07 mol% in the solvent. This result demonstrated that lower Al addition than previous report [13] contributes to the replication of 4H-SiC and allows the growth of low resistivity n-type 4H-SiC crystal. Insert Fig. 6 here.

As an example, a side view, plain view, and cross-section of a 1.5-mm-thick crystal grown for 12 h from Si–40mol%Cr-based solvent with 0.05 mol% Al addition are shown in Fig. 7. The crystal was 4H-SiC across the entire growth interface. As shown in Fig. 7(b), six segments at the periphery of the growth interface were observed and the shape of growth interface approached hexagonal with Al addition to the solvent. As seen in Fig. 7(c), (11ത02ത) facet formation was clearly observed and their width was much larger than that grown from the Si–40mol%Cr-based solvent, shown in Fig. 2. This suggested that the (11ത02ത) facet tends to be more stabilized by Al addition than others. Mitani et al. [17] reported that the edges of ത 02) planes and suggested the giant macrosteps on the grown interface faceted most frequently into (11 (11ത02) plane to be the most thermodynamically stable facet after the (0001ത) plane. According to the blue color of the faceted region shown in Fig. 7(c), it was speculated that higher Al incorporation at the facet overcompensated for doped nitrogen. Shirai et al. [18] reported that blue- to dark-blue-colored p-type 4HSiC crystals formed by doping high concentrations of Al in a TSSG process, so Al concentration into the outmost region seemed to be higher than that into the other region. The width of the blue-colored region 7



gradually increased from the early stage of growth and reached an almost constant width of 0.3 mm. Insert Fig. 7 here ത ) plane To determine the difference in dopant incorporation between step flow growth on the (0001 ത ) facet growth, the polytype and carrier concentration of a layer grown from Si–40mol%Cr– and (11ത02 0.1mol%Al solvent were measured by Raman spectroscopy, as shown in Fig. 8. Analysis of the range of the folded transverse acoustic (FTA) phonon mode in Fig. 8(b) showed the presence of the 204 cm−1 band, ത 02ത) facet growth area. In Fig. which characterizes 4H-SiC, across the entire interface, including the (11 8(c), the central wave number for the broad LO phonon mode ranged from 960 to 975 cm−2 in most areas, but was 975–985 cm−2 at the (0001ത) circular plane and about 950 cm−2 at the (11ത02ത) facet. Figure 9 shows the distribution of the carrier concentration at the periphery, as estimated from the LO-phonon mode along the direction of [112ത0]. The carrier concentration was about 1.2 × 1018 cm−3 at the (0001ത) plane and ത 02ത) facet. According to the about 1.6 × 1017 cm−3 at the periphery with a 0.75 mm width of the (11 existence of a p-type layer, assumed from the blue color of the faceted region shown in Fig. 7(c), it was speculated that higher Al incorporation at the facet overcompensated for doped nitrogen. Therefore, it was determined that Al incorporation differed for growth on the (11ത02ത) facet compared with that on other planes. Insert Figs. 8 and 9 here. 3. Effect of Al Addition into Si–Cr-based Solvent on Stability of Growth Planes of 4H-SiC In Section 2, non-uniform dopant incorporation in different growth planes was observed. The effect of Al addition to the solvent on Al incorporation and the stability of different growth planes was further investigated. The surface roughness of grown crystals, as measured by laser microscopy, was taken as a measure of the stability of the growth planes. ത 01 ത ), Figure 10 shows the surface morphologies and roughnesses of crystals grown on (0001ത), (11 ത 02ത) seeds from Si–40mol%Cr-based solvent. The surface of the layer grown on the (0001ത) seed and (11 ത 02 ത ) seeds were composed of large terraces and comprised dense steps, while those on the (11ത01ത) and (11

8


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ത 01ത) and (11ത02 ത ) seeds were one order of deep grooves. The surface roughnesses of the layers grown on (11 ത ) seed. magnitude higher than that on (0001 Insert Fig. 10 here. ത 0m ഥ )(m Figure 11 shows surface morphologies and roughnesses of crystals grown on (0001ത) and (11 = 0, 1, 2, 3, 4) from Si–40mol%Cr-based solvent with 2 mol% Al addition. The surface of the layer grown on (0001ത) seed comprised microsteps of less than 100 nm in height and its roughness was lowest among the planes investigated. The surface roughness of the layer grown on (11ത02ത) seed was lowest of all ത ) plane is the stable facet. The surface roughnesses of layers ഥ ) faces, which indicated that the (11ത02 (11ത0m ത 02ത) seeds from the solvent with Al were smaller than those from the grown on (0001ത), (11ത01ത), and (11 base solvent. In particular, the roughness on (11ത02ത) seed was one-tenth in the presence of Al addition to the solvent, indicating that this improved the stability of the (11ത02ത) plane during solution growth. Insert Fig. 11 here. Al concentrations in the middle of the surfaces of various grown crystals were analyzed by SIMS and are shown in Fig. 12. Different Al concentrations were found when changing the growth planes of the ത 01 ത ) seed, followed by those on (0001) seeds. The Al concentration was largest on crystals grown on (11 and (11ത02ത) seeds. The atomic arrangements at the cross-sections perpendicular to the 4H-SiC (0001), ഥ ) (m = 1–4) planes at the surface are shown in Fig. 13. The (0001) plane is covered by (0001ത), and (11ത0m Si atoms with single dangling bonds before surface relaxation. When a Si site at the surface is substituted by an Al atom, trihedral coordination of Al provides electroneutrality by covalent bonding with three surrounding C atoms. Such an effect is expected by density functional theory calculation, which predicts a decrease in the surface energies of the 4H-SiC (0001) and 6H-SiC (0001) planes when Al is doped to the crystal [11]. On the contrary, Al doping leads to an increase in the surface energy of the (000-1) plane because the surface is composed of C atoms [11], implying that Al incorporation on (000-1) plane is less likely to occur. The Al concentration in crystal grown on (0001) seed was 2.5 times larger than that on (0001ത) seed, which might be explained by preferential adsorption of Al at the (0001)/solution interface by substitution in a Si site caused by electrochemical interaction, as is the case at the surface. On the contrary, 9



as C atoms cover the surface of (000-1) plane, excess Al incorporation by adsorption does not occur. Fifty ത 01ത) and (11ത02ത) planes had a single dangling bond. percent of Si atoms at the surfaces of the 4H-SiC (11 The larger Al concentrations of layers grown on seeds with the planes than that on (0001ത) seed is also explained by trihedral coordination of Al substituting for Si sites at the surface, resulting in Al incorporation in the grown crystal, although the reason for the highest Al concentration on the (11ത01ത) seed is still not clear. The lower carrier concentration at the (11ത02ത) facet in Fig. 9 was thus caused by charge compensation attributed to the higher Al concentration. Considering that preferential adsorption stabilized ത 02 ത ) plane by decreasing the interfacial energy, it was speculated that Al addition to the solvent the (11 contributed to stabilizing (11ത02ത) facet formation. Insert Figs. 12 and 13 here.

4.

Mechanism for 4H-SiC Replication in Solution Growth on Concave Surface and the Effect of

Aluminum ത 02 ത ) facet was found to be key to replicating 4H-SiC during SGCS (Section 1) Formation of the (11 and its stability was increased by Al addition to the Si–Cr-based solvent (Sections 2 and 3). Based on these data, we propose a mechanism for replicating 4H-SiC during SGCS. Figure 14 shows atomic arrangements of the surface inclined 63° from the (0001ത) planes of 4H-, 6H, 3C-, and 15R-SiC, which corresponds to the (11ത02ത) facet of 4H-SiC. In contrast to (0001ത), 4H-SiC (11ത02ത) is inclined and has no common surface structure with other polytypes. In addition, the outmost atoms of the (0001) plane exhibit periodic unevenness. Accordingly, as shown in Fig. 15, when (11ത02ത) facets form at the periphery of a growth interface as growth tips, this automatically leads to replication of 4H-SiC without any other polytype, possibly by adhesive growth. At the edge of the facets, a flat (0001ത) plane is formed, which supplies steps directed to the central part of the crystal while keeping the 4H-SiC ത ) rather than (0001ത), Al addition stacking sequence. Because Al is preferentially incorporated into (11ത02 to the solvent stabilizes the (11ത02ത) plane. Such stabilization enhances the replication of 4H-SiC across the entire growth interface. 10


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Insert Figs. 14 and 15 here.

Conclusions To investigate the mechanism of 4H-SiC replication during solution growth on a concave surface, ത ) seed and on 0.5-inch square seeds of different planes was SiC growth on 2-inch-diameter 4H-SiC (0001 carried out at 2273 K using Si–40mol%Cr-based solvent with and without Al addition. The following results were obtained: ത ) facets at the periphery of the growth interface (1) Grown crystal that replicated 4H-SiC possessed (11ത02 and its growth tips were located at both edges of such facets; (2) Al addition to the solvent enlarged (11ത02ത) facets at the growth interface and increased the probability ത ) seed contained higher Al concentrations and for 4H-SiC replication. Furthermore, layers grown on (11ത02 lower roughness; hence, preferential adsorption of Al on (11ത02ത) was presumed. Based on these observations, we proposed a mechanism for 4H-SiC replication during SGCS ത 02 ത ) facet formation because the growth tip comprising a contribution, not of spiral growth, but of (11 replicates 4H-SiC due to the specific atomic arrangement of the plane, which subsequently supplies step ത 02ത) facets at the periphery, flow to the central part of the crystal. Al addition to the solvent stabilizes (11 resulting in a higher probability of 4H-SiC replication.

Acknowledgment The authors are grateful for the helpful discussions with Motohisa Kado of Toyota Motor Company. We thank Kathryn Sole, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.

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18. Shirai, T.; Danno, K.; Seki, A.; Sakamoto, H.; Bessho, T. Solution Growth of p-Type 4H-SiC Bulk Crystals with Low Resistivity, Mater. Sci. Forum 2014, 778, 75-78.

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Figure 1

Figure 2

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Figure3

Figure 4

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Figure 5

Figure 6

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Figure 7

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Figure 9 18


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Figure 10

Figure 11

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Figure12

Figure 13

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Figure 14

Figure 15

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Captions List

Figure 1. Schematic illustration of top-seeded solution growth method. Figure 2. 4H-SiC-replicated crystal of 2-inch diameter by solution growth on a concave surface (SGCS) using Si–40mol%Cr-based solvent. (a) Side view, (b) surface view, and (c) cross-section parallel to

{112ത0} plane of grown crystal. (d) Nomarski image of periphery region. Figure 3. 6H-SiC-converted crystal of 2-inch diameter by solution growth on a concave surface (SGCS) using Si–40mol%Cr-based solvent. (a) Side view, (b) surface view, and (c) cross-section parallel to

{112ത0} plane of grown crystal. Figure 4. (a) Schematic image of preparation of 4° off wafer from grown crystal; (b) surface morphology of prepared wafer after molten KOH etching.

Figure 5. Al and N concentrations in 4H-SiC crystal grown from Si–40mol%Cr-based solvent with Al addition.

Figure 6. Dependence of probability of 4H-SiC polytype and resistivity of grown crystal of 2-inch diameter on Al concentration in solvent.

Figure 7. 4H-SiC-replicated crystal of 2-inch diameter by solution growth on a concave surface (SGCS) using Si–40mol%Cr-based solvent with 0.05 mol% Al addition. (a) Side view, (b) surface view, and (c) cross-section parallel to {112ത0} plane of grown crystal.

Figure 8. Distribution of Raman shifts of crystal surfaces grown from Si–40mol%Cr-based solvent with 0.1mol% Al addition at 2273 K.

ത 0] direction at the periphery of crystal grown from Figure 9. Estimated carrier concentration along [112 Si–40mol%Cr-based solvent with 0.1mol% Al addition.

ഥ ) seeds using Si–40mol%CrFigure 10. Surface morphologies of layers grown on (0001ത) and (11ത0m based solvent.

ഥ ) seeds using Si– Figure 11. Surface morphologies of layers grown on (0001ത), (0001), and (11ത0m 40mol%Cr-based solvent with 2 mol% Al addition. 22


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Figure 12. Al concentrations in layers grown on different planes from Si–40mol%Cr-based solvent with 2 mol% Al addition.

ത 02 ത ) surfaces of 4H-SiC. Figure 13. Atomic arrangements in cross-sections across (0001), (0001ത), and (11 ത ) planes of Figure 14. Atomic arrangements in cross-sections across the surface inclined 63° from (0001 4H-, 6H-, 3C-, and 15R-SiC.

ത 02ത) facets. Figure 15. Schematic illustrations of mechanism for replicating 4H-SiC by growth of (11

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For Table of Contents Use Only Title: Mechanism of Replicating 4H-SiC Polytype by Solution Growth on Concave Surface

Authors: Hironori Daikoku*1, Sakiko Kawanishi2, Takeshi Yoshikawa1

TOC graphic

Brief synopsis (60 words or less) Analysis of the growth interface of 4H-SiC crystals obtained by solution growth on a concave surface showed that 4H-SiC replication was achieved by formation of (11ത02ത) facets at the periphery of the growth interface at the growth tip. Al addition to the Si–Cr–based solvent stabilized the (11ത02ത) facets, thereby increasing the probability of 4H-SiC replication.

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Mechanism of Replicating Polytype of 4H-SiC by Solution Growth on

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