776 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



5.0 



4.5 



4.0 



3.5 



3.0 



< 



J 2-5 



2.0 



1.5 



1.0 



0.5 

 



0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 



CURRENT, le, IN MILLIAMPERES 



5.0 



Fig. 3 — Comparison of alpha-emitter-current characteristics of formed points. ,' I 



increase in the drift field near the point and a corresponding increase in 

 a. Fig. 3 indicates that such is the case. The small signal a is plotted as 

 a function of emitter current in Curves I and II. The point spacing in 

 this case is 2.5 mils. It is interesting to note that the peak at low emitter 

 currents is present in both cases, in spite of the fact that presence of a 

 p-n hook is not likely when the Be-Cu point is formed. 



It is thus apparent that the forming the Be-Cu point produces a struc- 

 ture which more closely resembles a p-n junction. The effect of adding 

 the donor is to reduce the resistance of the junction. Further contrast 

 between these two kinds of contacts is demonstrated by comparing for- 

 ward currents through the contacts and their capacities. In Table I, a 

 summary of all the contrasting properties is given. All values quoted 

 are representative values. 



2.2.2 Use of the Copper Plating Technique 



During the investigation of these contact properties, an interesting way 

 of illustrating their physical properties was developed. This technique, 

 borrowed from junction transistor technology, can be used to identify 

 visually the boundary between the formed region and the bulk genua- f^ 

 nium in a metallographic section of a point-contact transistor. It further 

 appears that modifications of the technique will enable determination of k: 



