POINT-CONTACT TRANSISTOR SURFACE EFFECTS 785 



these points approaches values found in electrically formed collectors. 

 Subsequent parts of this section will be concerned with description of the 

 experiments involved and comparison of the electrical characteristics of 

 these points with those of conventionally formed points. 



The effections of electrical forming on donor-doped and donor-free 

 point contacts have been described in earlier sections. It has been stressed 

 that the addition of the donor element to the point results in a contact 

 with degraded diode characteristics, but which serves as an excellent 

 collector. 



The possibility of an analogous situation in an unformed point collec- 

 tor exists, with the electrical forming of the donor-doped point being 

 replaced by a suitable chemical treatment of the surface. The experi- 

 ments described below indicate that such is the case. 



3.2 Experimental Procedures 



The germanium used in these experiments was zone-leveled material. 

 The n-germanium was in the 3 to 4 12-cm range. Originally, experiments 

 were run using slices, about 0.025 in thickness, soldered on flat brass 

 blocks, with the brass well masked with polystyrene. Germanium dice, 

 already mounted on standard base-header assemblies used in a hermetic- 

 seal transistor process pilot line, were also used. 



The ground surface of a slice was given a three-minute chemical etch 

 (CP4 or superoxol), washed in pure water (conductivity <0.1 micromho), 

 and blown dry in a nitrogen stream. This surface could then be exposed 

 for several minutes to 24 per cent HF, hot zinc chloride-ammonium chlo- 

 ride solder flux, or other chemical treatments as the experiment might 

 require. These solutions were applied to the slice or die in the form of 

 large droplets, so the solution did not come in contact even with the 

 masking. Later, in order to make doubly sure that contamination from 

 the base or base contact was not involved, all experiments were repeated 

 using a two-inch length of a zone leveled bar with a base contact soldered 

 on one end, and the other end, freshly ground between treatments, used 

 as the surface under examination. The etching was done by lowering 

 one end of the bar about one-half inch into the etch, leaving the contact 

 end a good distance from the etch. The etched surface could subsequently 

 be exposed to any desired chemical treatment. After the chemical treat- 

 ment, the sample surface was again washed in low conductivity water 

 for several minutes and blown dry with nitrogen. 



The sample, after chemical treatment, was placed on a double ended 

 manipulator base, used to control the position and pressure of two canti- 



