470 BELL SYSTEM TECHNICAL JOURNAL 



current flow. When the contact is biased in the reverse (negative) direc- 

 tion, these holes tend to flow toward the contact and contribute to the 

 current. The hole current is increased if the concentration of holes in the 

 germanium is enhanced by injection from a neighboring contact or by 

 creation of electron-hole pairs by light absorption. 



Much has been learned about the effect of an added hole concentration 

 on the current voltage characteristics of contacts from studies with 

 germanium filaments. Part of this work is summarized in a recent article 

 of W. Shockley, G. L. Pearson and J. R. Haynes.^ These authors have 

 investigated the way the low-voltage conductance of a point contact to a 

 filament of «-type germanium varies with the concentration of holes in 

 the filament and have shown that there is a linear relation betw-een con- 

 ductance and hole concentration. They have shown that the current to a 

 contact biased with a large voltage in the reverse direction varies linearly 

 with hole concentration. Suhl and Shockley^ have shown that by applying 

 a large transverse magnetic field along with a large current flow holes 

 may be swept to one side of the filament. Changes in hole concentration 

 produced in this way are detected by measuring changes in the con- 

 ductance of a point contact. 



Shockley^ has suggested that the floating potential measured by a con- 

 tact made to a semiconductor in which the concentration of carriers is 

 not in thermal equilibrium may depend on the nature of the contact and 

 differ from the potential in the interior. Pearson^ has investigated this 

 effect for point contacts on germanium filaments, and has shown that the 

 floating potential is related to the conductance of the contact. This effect 

 provides an explanation for anomalous values of floating potentials meas- 

 ured by Shockley^ and by W. H. Brattain.^ They found that potentials 

 measured on a germanium surface in the vicinity of an emitter point 

 biased in the forward direction may be considerably higher than expected 

 from the conductivity of the material. 



The purpose of the present paper is to develop the theory of these rela- 

 tions. We are particularly interested in effects produced by changes in 

 hole concentration in w-type germanium resulting from hole injection or 

 photoelectric effects. The equations developed also apply to injected 

 electrons in />-type semiconductors with appropriate changes in signs of 

 carriers and bias voltages. The methods of analysis used are similar to 

 those which have been cm])loyed by l^rattain and the author in a dis- 

 cussion of the forward current in germanium point contacts-. 



^ H. Suhl and W. Shockley, Phys. Rev. 74, 232 (1948). 



" W. Shockley, Bell Sys. Tech. Jour. 28, 435 (1949), p. 468. 



" Unpublished, 



