ELECTROLYTIC SHAPING OF GERMAXIUM AND SILICON 



341 



Fig. 7 — Electrolytic etch pits on n-type germanium. 



high donor concentration would favor breakdown, as would any con- 

 cavity of the germanium surface (which would cause a higher field for 

 a given voltage) . Very high fields must occur at the points of spikes such 



jas those shown in Fig. 7. The continued growth of the spikes is thus 

 favored by their geometry. 



Microscopic etch pits arising from chemical etching have been corre- 



;lated with the edge dislocations of small-angle grain boundaries. A 



I specimen of n-type germanium with chemical etch pits was photomicro- 

 graphed and then etched electrolytically. The etch pits produced elec- 

 trolytically could not be correlated with the chemical etch pits, most 

 of which were still visible and essentially unchanged in appearance. 

 Also, no correlation could be found between either kind of etch pit and 

 the locations at which copper crystallites formed upon immersion in a 

 copper sulfate solution. Microscopic electrolytic etch pits at dislocations 



j in p-type germanium have been reported in a recent paper that also 

 I mentions the deep pits produced on n-type germanium.^* 

 y Electrolytic etch pits are observed on n-type and high-resistivity 

 silicon. These etch pits are more nearly round than those produced in 

 germanium. 



In spite of the pitting phenomenon, electrolytic etching is success- 



