Kimito Nishikawa

Improved Surface Morphology and Background Doping Concentration in 4H-SiC(000-1) Epitaxial Growth by Hot-Wall CVD

4H-SiC layers have been homoepitaxially grown on off-axis 4H-SiC(000-1) under various conditions by horizontal hot-wall CVD. Improvement of surface morphology and reduction of background doping concentration have been achieved. Surface morphology grown on the (000-1) C face strongly depends on the C/Si ratio at 1500 °C, and hillock-like surface defects can be eliminate by increasing growth temperature to 1600 °C. Site-competition behavior is clearly observed under low-pressure growth conditions even on the (000-1) C face. The lowest doping concentration has been determined to be 6.0x1014 cm-3. A trial of high-speed growth on the (000-1) C face and deep level analysis are also discussed.

Frank Partial Dislocation in 4H-SiC Epitaxial Layer by MSE Method

We have been trying to improve a quality of crystal, using the metastable solvent epitaxy (MSE) method, one of the solution methods. In MSE, a Frank-type fault is formed by conversion of a threading screw dislocation (TSD) in the substrate. To study the status of the growth, we performed plane-viewed TEM observation. Analysis of Burgers vectors in the TEM image showed Frank PDs (Partial Dislocations) which do not include a components and Frank PDs which include a components. The total Burgers vectors of Frank-type fault including a components are represented as b=a/3+c, which indicates some TSDs in the substrate also include a components.

Real Relationship between Acceptor Density and Hole Concentration in Al-Implanted 4H-SiC

Al-implanted p-type 4H-SiC layers with different conditions of implantation and annealing temperatures are formed, and the temperature dependence of the hole concentration ) (T p in the p layer is obtained from Hall-effect measurements. In order to determine the reliable acceptor density ( A N ) from ) (T p , it is found that the Fermi-Dirac distribution function is not appropriate and that a distribution function including the influence of the excited states of Al acceptors is required. This is because the Al acceptor level in SiC is deep (~180 meV) and because its first excited state level, which is calculated by the hydrogenic model, is still deep (~35 meV), which is close to the acceptor level of B in Si. It is demonstrated that the proposed distribution function is suitable for obtaining the actual relationship between A N and ) (T p .

Epitaxial Growth of 4H-SiC on 4º Off-Axis (0001) and (000-1) Substrates by Hot-Wall CVD

4H-SiC layers have been homoepitaxially grown on 4°off-axis (0001) and (000-1) under various conditions by horizontal hot-wall CVD. We have investigated surface morphology and background doping concentration of the epi-layers on 4°off-axis substrates. Surface morphology grown on the (0001) Si-face showed strong step bunching under C-rich conditions. On the other hand, smooth surface morphology on the (000-1) C-face could be grown in the wide C/Si ratio range at 1600 °C. Site-competition behavior is clearly observed under low-pressure growth conditions on 4°off-axis (000-1) C-face, leading to a lowest doping concentration of 4.4x1014 cm-3.

Dependence of Hole Concentration in p-Type Silicon Solar Cell Wafers on Temperature and on Position within the Polycrystalline Ingot

Conversion efficiency of polycrystalline silicon pn solar cells, which are fabricated using wafers sliced out of B-doped p-type poly-Si ingots, strongly depends on where it is taken from within the ingot. Since the wafers near the bottom or top of the ingot cannot be used for commercial solar cells, the relationship between the conversion efficiency and the temperature dependence of the hole concentration in poly-Si wafers is investigated. It is found that the hole concentrations are classified into three categories. In wafers near the bottom of the ingot it is abnormal because it shows a peak, while the behavior in wafers near the top results from the incorporation of another acceptor species into the wafers or the creation of defects in the wafers besides B acceptors.