Akinori Seki

MOCVD Growth of InP on 4-inch Si Substrate with GaAs Intermediate Layer

This letter describes the heteroepitaxy of InP on Si by MOCVD. A new epitaxial structure with a thin GaAs intermediate layer (InP/GaAs/Si) is proposed to alleviate the large lattice mismatch (8.4%) between InP and Si. Using this structure, a 4-inch InP single crystal with a mirror-like surface and good thickness uniformity (Δd/d=±10%) was obtained. Residual stress in the InP film was 5.7±108 dyn/ cm2 for the InP/GaAs/Si structure, as compared to 8.3×108 dyn/cm2 for the InP directly grown on Si. This shows that the GaAs intermediate layer is also effective in reducing the residual stress in the InP epilayer.

High-Speed Growth of High-Quality 4H-SiC Bulk by Solution Growth Using Si-Cr Based Melt

High-speed solution growth using Si-Cr based melt has been performed on on-axis 4H-SiC(0001) at a high temperature of about 2000°C. The maximum growth rate for one-hour growth reaches to 1120 m/h, while the typical growth rate of growth for 2h is about 500 m/h. A large crystal that is about 25 mm in diameter and 1650 m in thickness can be obtained by growth for 5h. The crystal quality is confirmed to be homogeneous by X-ray diffraction and X-ray topography, because FWHM is less than 30 arcsec. Etch pit density of the threading dislocations in the grown crystal is 103-104 cm-2, and that of basal plane dislocation is 2×102-3×103 cm-2. Resistivity of the crystals grown by the solution growth is comparable to those of crystals grown by physical vapor transport technique.

Interface Properties of SiO2/4H-SiC(0001) with Large Off-Angles Formed by N2O Oxidation

In this study, we have investigated N2O oxidation of various off-angled 4H-SiC (0001) epilayers and characterized the properties of MOS interfaces. The oxide thickness almost linearly increases with increasing off-angle. Oxidation on highly off-angled (0001) 4H-SiC is faster than that on 8o off-axis (0001). The off-angle dependence of Dit is very small for the MOS capacitors in the off-angle range from 8o to 30o. The depth profiles of carbon and nitrogen atoms near the MOS interface on 15o off-axis 4H-SiC(0001) are similar to those on 8o off-axis (0001).

Diffusion of Transition Metals in 4H-SiC and Trials of Impurity Gettering

The diffusion of transition metals in 4H-SiC has been investigated by secondary ion mass spectrometry using epilayers and substrates implanted with titanium (Ti), chromium (Cr), iron (Fe), or nickel (Ni). Implanted Cr, Fe, and Ni atoms diffuse by subsequent Ar annealing at 1780 °C in n-type 4H-SiC epilayers. In n+-type substrates, the diffusivities of Ti, Cr, and Fe are almost negligible, while only Ni diffuses. By the helium implantation following the implantation of transition metals, no diffusion of Ti, Cr and Fe is observed in epilayers. The diffusion of transition metals in SiC is discussed based on the results of first-principles calculation.

Solution Growth of p-Type 4H-SiC Bulk Crystals with Low Resistivity

P-type 4H-SiC bulk crystals have been grown at a high growth rate of 1.0 mm/h by solution growth using Si-Cr-Al based melt. The crystals grown from solution with an Al content of 10at% show low resistivity of 35 mcm, which is two orders of magnitude lower than commercialwafers (Resistivity: 2500 mcm). The low-resistivity crystals have flat surface and few solvent inclusions. These results indicate that solution growth is a suitable method for fabricating low-resistivity p-type substrates with low cost.

Dislocation Behavior in Bulk Crystals Grown by TSSG Method

The dislocation behavior during bulk crystal growth on the 4H-SiC (000-1) C-face using the solution method was investigated. A 2 inch wafer with a 4° off angle was fabricated from a bulk crystal grown by the TSSG method, and the dislocations in the crystal were evaluated using synchrotron X-ray topography and TEM observation. From the topograph images, it was found that the TSD density remarkably decreased as the growth progressed. Furthermore, the TEM observation suggested that TSD decreases as the threading dislocations convert to in-plane defects toward the center of the crystal. Conventionally, it was considered that conversion of threading dislocations hardly occurs in solution growth on the C-face. However, it is thought that this phenomenon was not observable because the conversion efficiency is remarkably low. We speculate that dislocations may be transformed by suddenly making macrosteps during bulk growth.

Influence of Dislocations to the Diamond SBD Reverse Characteristics

Several studies have been carried out regarding the influence of dislocations on device characteristics; however, most of them had been limited to pseudo-vertical structures using high pressure high temperature (HPHT) insulating material as the substrate. In this study, we have investigated the influence of dislocations to the devices using vertical structure SBD on p+ HPHT substrate. SBDs were selectively fabricated on specific dislocation areas. The SBD fabricated on the threading dislocation area indicated fatal influence of the dislocation on the device characteristics.

Characterization of insulated-gate bipolar transistor temperature on insulating, heat-spreading polycrystalline diamond substrate

Polycrystalline diamond films have been utilized as direct bonding aluminum (DBA) substrates to improve cooling efficiency. A diamond film with a high quality factor was characterized by Raman spectroscopy and showed a high thermal conductivity of more than 1800 W m−1 K−1 and a low leakage current, even at an applied bias of 3 kV, because of the suppression of electrical conduction through the grain boundaries. The operating temperatures of Insulated-gate bipolar transistors (IGBTs) on diamond DBAs were 20–28% lower than those on AlN DBAs. The thermal resistivity of the diamond DBA module was 0.32 °C/W. The uniformity of the temperature distribution on a diamond DBA was excellent.

Solubility and diffusion of chromium in 4H-SiC

The solubility and diffusivity of Cr atoms in 4H-SiC epilayers are investigated. The formation energy of 4H-SiC containing Cr has been calculated by first-principles calculation. Si sites have been found to be more stable than C sites or interstitial sites for Cr atoms owing to the lower formation energy. The solubility estimated from the formation energy coincides with the saturated Cr concentration in SiC crystals grown by solution growth. The diffusivity of implanted Cr atoms (located at interstitial sites) was not affected by the charge states of Cr atoms and/or vacancies such as carbon vacancies and silicon vacancies, implying the interstitial diffusion of Cr atoms.

Diffusion and Gettering of Transition Metals in 4H-SiC

Diffusion of transition metals in 4H-SiC has been investigated by secondary ion mass spectroscopy using epilayers and substrates implanted with titanium (Ti), chromium (Cr), iron (Fe), or nickel (Ni). In the epilayers, Cr, Fe, and Ni atoms have diffused by argon (Ar) annealing at 1780°C for 30 min. In n+ substrates, the diffusivity of the metals is smaller than that in the epilayers, and only Ni has diffused by the annealing. By the Ar or helium implantation following the implantation of transition metals, diffusion of transition metals can be successfully suppressed.