POINT-CONTACT TRANSISTOR SURFACE EFFECTS 



777 



Table 1 



the equipotentials surrounding a collector or emitter point under bias, 

 and visualization of current flow patterns in point contact transistors 

 under bias operating conditions. 



Use of this technique in identification of formed transistor properties 

 is quite simple. A transistor container (including only the completed 

 header, wafer, and point-contact structure) is filled with araldite plastic, 

 which is allowed to harden. The collector point is then electrically formed. 

 The plastic is necessary to ensure that the collector point does not subse- 

 quently move from the formed area. The can itself is then embedded in a 

 plastic block, which is lapped down to expose a cross section of the unit. 

 Fig. 4(a) and (b). Both the collector point and the base electrode are well 

 masked. Fig. 5. A droplet of CuS04 solution of fairly low concentration 

 is placed on the germanium, so that it is in physical contact only with 

 with the germanium and the masking plastic. In order to identify the 

 formed region, a reverse bias of 20 volts or so is applied between the 

 collector point and the base contact for a time usually of 0.1 second or 

 less. Actually, best results have been obtained by applying the reverse 



PLASTIC -=r- 



PLASTIC BLOCK 



(a) 



Fig. 4 — Preparation of a transistor for copper plating. 



