ELECTROLYTIC SHAPING OF GERMANIUM AND SILICON 347 



In general, smooth etching of siHcon seems to result when the effective 

 valence is nearly 4 and there is little anodic evolution of gas. The elec- 

 I trical properties of the smooth surface appear to be equivalent to those 

 ! of smooth silicon surfaces produced by chemical etching in mixtures of 

 i nitric and hydrofluoric acids. On the other hand, the reactive surface 

 [produced at a valence of about 2, with anodic hydrogen evolution, is 

 I capable of practically shorting-out a silicon p-n junction. The electrical 

 j properties of this surface tend to change upon standing in air. 



ACKNOWLEDGEMENTS 



Most of the experiments mentioned in this paper were carried out by 

 my wife, Ingeborg. An exception is the double-dimpling of germanium 

 by light, which was done by T. C. Hall. The dimpling procedures of 

 Figs. 9 and 10 are based on suggestions by J. M. Early. The effect of 

 light upon electrolytic etching was called to my attention by 0. Loosme. 

 W. G. Pfann provided the germanium crystals grown with different 

 degrees of stirring. 



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