Large-area X-ray and CL study of SI GaAs wafers from various suppliers

Abstract

Homogeneity of electrical and structural properties of SI GaAs wafers is very important for implantation technology. Reflection Lang X-ray topography and integral cathodoluminescence have been used to characterize the inhomogeneities of wafers from various suppliers. Scratches, slip dislocations, cellular structure, and lineages have been observed with significant differences in distribution, density, species, and shape of the extended defects not only from supplier to supplier but also when comparing seed and tang ends of the same crystal. Direct correlation between Lang XRT and CL has been found for scratches, lineages and cell walls, but not for slip dislocations. Complex dark/white contrast of various features in CL images has been described. Besides white contrast at the cell walls, white islands inside the cells have been observed as well. The observations have been interpreted on the basis of the concept of cellular structure and slip dislocations formation and on the basis of point defect oversaturation and nucleation of As-rich precipitates capable of gettering.