Formation of Abnormal Etch Pits on (111)P Surface of n-GaP Crystal

When (111) wafers of Te-doped GaP were etched in H2SO4+H2O2+H2O (5:1:1 in volume ratio) at a temperature above 70°C for a period longer than 3.6×103 s, abnormal etch pits of asymmetric shape formed on the (111)P surface in minor density compared to those of normal triangular pits and spiral pits. From microscopic observation, the abnormal pit had an etch beak projecting from its apex. In order to clarify the origin of abnormal etch pits, structural defects in the wafers were examined by transmission electron microscopy after thinning. As a result, they were classified into several types such as dislocations, dislocation loops, precipitates and lineage defects composed of a dislocation bundle. As the lineage defects often take such a peculiar configuration as a zigzag pattern, we suppose that the abnormal etch pit with a beak would nucleate owing to preferential dissolution along the lineage defect.