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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



-METAL 



n-TYPE SEMICONDUCTOR- 



Fig. 9 — Electron energy diagram for a metal -semiconductor contact. 



The experiments of Brown^ indicate that the presence of charge on 

 the surface of p-germanium can alter the space charge in the crystal 

 near its surface and, in some cases, produces an inversion layer of n- 

 germanium at the surface. Garrett and Brattain^° have shown that a 

 change of ambient from sparked oxygen to dry oxygen to wet oxygen 

 can increase Ico and floating potential on n-p-n junction transistors, and 

 the process is reversible. Their interpretation is that sparked oxygen 

 builds up a film, presumably germanium oxide. Oxygen atoms on the 

 surface, negatively charged, can give rise to a p-type inversion layei on 

 n-germanium. Moisture apparently counteracts this negative charge, 

 and humid oxygen can cause an n-type inversion layer on p-germanium, 

 which can be removed with a dry oxygen ambient. 



Thus, the electrical resistance of an unformed metal-germanium con- 

 tact on an etched germanium surface can be expected to be extremely 

 sensitive to any chemical treatment which tends to affect the constitu- 

 tion of the oxide layer present on the surface, regardless of the metal 

 used for contact in air. Bardeen and Brattain,^ in early transistor ex- 

 periments, have shown that such is the case. They have used transistor 

 collector points on germanium surfaces which, after etching, were sub- 

 jected to an oxidation treatment (heating in air). 



In this section are described experiments which seem to indicate that 

 the reverse resistance of unformed diodes on etched n-germanium sur- 

 faces can be decreased by chemical surface treatment, and the magnitude 

 of the floating potential near such contacts is increased to sufficient ex- 

 tent that the point can serve as a multiplying collector. Average a for 



