Naoyoshi Komatsu

Growth Rate and Surface Morphology of 4H-SiC Single Crystal Grown under Various Supersaturations Using Si-C Solution

We have investigated growth rate and surface morphology of 4H-SiC single crystal grown from Si-C solution with various supersaturation levels at growth temperature in the range from 1840 to 2140 °C. The growth rate depends linearly on the amount of supersaturated carbon, irrespective of the growth temperature. This indicates that the growth is limited by the transfer of solute element onto the crystallization front. The adequate condition for stable solution growth are discussed with respect to high growth rate and surface morphology.

4H-SiC Growth from Si-Cr-C Solution under Al and N Co-Doping Conditions

We have investigated the solution growth under various Al-N co-doping conditions. Both p-type and n-type 4H-SiC were successfully grown under Al-N co-doping conditions, while using the effect of Al-addition to stabilize both growth surface and polytype. The doping and electrical properties were investigated systematically. Interaction between Al and N in the incorporation process and electrical property under heavily co-doped conditions were discussed.

Change in Surface Morphology by Addition of Impurity Elements in 4H-SiC Solution Growth with Si Solvent

In solution growth of 4H-SiC, we have investigated changes in macrostep height with addition of the Group III (B, Al, Ga), Group IV (Ge, Sn), Group V (N) elements, and transition metals (Ti, V, Cr, Ni) to Si solvents, in order to find additives improving severe step bunching which often occurs during growth. The addition of Al, B, Sn, N, and V decreased the average macrostep height compared with the crystal grown with Si solvents. The addition of Al, B, Sn, N, and V suppressed the generation of trench-shaped surface defects in long-term growth of 10 hours. This result demonstrated that the addition of Al, B, Sn, N, and V has an advantage to achieve high quality bulk crystal growth from solution.

Growth of 4H-SiC in Current-Controlled Liquid Phase Epitaxy

4H-SiC crystallization from Si-C solution in electric current-controlled liquid phase epitaxy was investigated. The dependence of growth speed on a DC current shows that dissolution/growth is controlled by the electric current without altering temperature gradient in the furnace. Application of an electric current leads to reduction of growth speed with negative polarity and enhancement of growth speed with positive polarity. The variation of the growth speed with a DC current density has been explained by the combination of the effects of electromigration of C solute and Joule heating.

Control of Void Formation in 4H-SiC Solution Growth

Void formation in 4H-SiC crystals grown from solution has been investigated by secondary ion mass spectrometry and Raman scattering. It becomes clear that ambient Ar gas is filled in voids and the solvent (Si) partially remains. The result indicates that Ar dissolved in the solvent vaporizes and forms bubbles. The trapped bubbles at the crystal growth front are considered to be incorporated in the growing crystal as voids. We also have developed following methods for suppression of the void formation; (1) dipping seed crystals so that the growth front faces upward, (2) growth under He atmosphere, and (3) the high temperature treatment of the solvent before crystal growth.

Influence of Additives on Surface Smoothness and Polytype Stability in Solution Growth of n-Type 4H-SiC

We have investigated the dependence of the macrostep height on various additives in solution growth of n-type 4H-SiC. Surface modification by adding transition elements in periods 4‒6 (Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, Ce, and W) and group 13‒14 elements (B, Al, Ga, Ge, Sn) was systematically studied to find additives improving smoothness of the growth surface. We found that Sc, Co, Mo, and Ge improved surface smoothness in addition to the already-known additives, such as Al, B, and Sn. Besides, these additives (Sc, Co, Mo, Ge) give no measurable influence on the conductivity of n-type grown crystals. These results demonstrated that Sc, Co, Mo, Ge and Sn are useful additives for solution growth of n-type 4H-SiC.

Modulation of Growth Rate by Electric Current in Liquid-Phase Epitaxy of 4H-SiC

The crystallization of 4H-SiC from Si–C solution in liquid-phase electroepitaxy (LPEE) at 1870 and 2050 °C was investigated. The growth of 4H-SiC was enhanced or suppressed by the application of DC with positive or negative polarity, respectively. By the application of AC, the Joule heating effect was separated from the effect of DC on LPEE. We showed that the effect of DC on LPEE consists of a linear electromigration effect and a quadratic Joule heating effect. The results demonstrate that growth rate can be controlled by adjusting not only temperature but also electric current. The variation of growth rate with temperature in LPEE was also examined, and it was shown that the electromigration effect can be controlled independently of the Joule heating effect by increasing the C concentration in the Si–C solution. At higher temperatures, the growth rate in LPEE can be improved without the enhancement of the Joule heating effect.