Three kinds of smooth pits not corresponding to edge dislocation on Ge (111) surface etched by CP4 solution were found by Muraoka
2). Round smooth pits are observed most usually among such pits. Shape of these pits and appearance of etched surface of samples with high density of these pits resemble those discovered by Tweet.
However, these pits are confirmed to differ from those corresponding to vacancy aggregate. Investigation is made to trace the origin of these pits. The pits are found similar to those that appear on Ge single crystals doped with silicon in oxidizing atmosphere. From the study on extinction phenomena of samples in infrared region, turbidity at λ=2.5μ and absorption coefficient at λ=9μ are found proportional to.1.5th power of round smooth pit density (Nc). Result of analysis on the wave length dependency of turbidity by the use of Mie's theory makes us infer that the pits are caused by silica particles included in Ge single crystal, which have average diameter of _??_1μ and the bulk density of _??_9×(Nc)
1.5.
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