I 



792 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



0.20 



0.10 

 0.08 



0.06 

 0.05 



0.04 

 0.03 



O 0.02 

 > 



t 

 0.010 



0.008 



0.006 

 0.005 

 0.004 



0.003 

 0.002 



0.001 



I 



0.1 



0.2 



0.3 0.4 



0.6 0.8 



1.0 



r 



2 

 IN MILS 



4 5 6 



8 10 



20 



Fig. 12 — Comparison of floating potentials for unformed point-contact col- 

 lectors. 



on the etched surface. It seems reasonable to ascribe the increased nega- 

 tive floating potential after the HF treatment to an increase in current 

 density through the surface under the point, rather than to any increase 

 in surface conductivity. It is worth noting that on superoxol-etched sur- 

 faces, the negative floating potential near an unformed collector point 

 can often be increased by an order of magnitude by blowing a stream 

 of dry nitrogen near the point. This effect may possibly be a result of 

 excess surface conductivity, but in these cases is not accompanied by any 

 appreciable changes in IdO, — 10) or average alpha. 



3.3.6 Contamination of Collector Points and Surfaces 



Past experience Avith use of point-contacts as transistor collectors indi- 

 cates that experiments may often be confused or confounded by unsus- 



