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BELL SYSTEM TECHNICAL JOURNAL 



That the space-charge layer which gives the rectifying barrier in ger- 

 manium arises from surface states, is indicated by the following: 



(1) Characteristics of germanium-point contacts do not depend on the 

 work function of the metal, as would be expected if the space-charge layer 

 were determined by the metal contact. 



(2) There is little difference in contact potential between different 

 samples of germanium with varying impurity concentration. Benzer^^ 



Fig. 15 — Schematic energj- level diagram of barrier layer at germanium surface show- 

 ing inversion layer of p-type conductivity. 



found less than 0.1-volt difference between samples ranging from n-type 

 with 2.6 X 10'^ carriers cm^ to p-type with 6.4 X 10'* carriers cm^. This 

 is much less than the difference of the order of the energy gap, 0.75 volts, 

 which would exist if there were no surface effects. 



(3) Benzer^" has observed the characteristics of contacts formed from 

 two crystals of germanium. He finds that in both directions the charac- 

 teristic is similar to the reverse characteristic of one of the cr^^stals in con- 

 tact with a highly conducting metal-like germanium crystal. 



