788 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



Table III 



Parameter 



/c(0, -10) ma. . 

 /c(6, —5) ma. . , 

 7c (0, +0.5) ma. 

 Peak value of a 

 a (5.0, -10).... 



After 3 Min. 

 Supero.xol Etch 



Max. Value 

 Observed 



-0.16 



-7.0 



2.8 



3.0 



0.50 



Min. Value 

 Observed 



-0.06 



-0.95 



2.0 



0.15 



0.09 



After Subsequent 10 Min. 

 "Soak" in 24% HF 



Max. Value 

 Observed 



- 0.98 



-13.5 



2.3 



6.0 



2.0 



Min. Value 

 Observed 



-0.20 



-7.0 



1.3 



2.0 



0.5 



no significant changes in the extreme values of IdO, —10) encountered 

 initially. Some of the unformed units have collector families quite simi- 

 lar to those of an electrically formed point-contact transistor. However, 

 the resemblance ends when stability of operation is considered. Wlien 

 the unformed units are operated in room ambient, hysteresis loops are 

 occasionally observed, either in the Ic-Vc output characteristic sweep, 

 or the a-emitter current sweep. This hysteresis can be eliminated by di- 

 recting a stream of dry nitrogen across the germanium surface in the , 

 vicinity of the points. It is not known whether the hj^steresis is thermal 

 or electrolytic in nature. The operation of these unformed units, even ; 

 in the absence of hysteresis, is extremely erratic and unstable. Operating ^> 

 a unit at a high power level will cause loss of a and Ico , and mechanical 

 shock delivered to the collector point while the unit operates under bias 

 may cause loss or gain of a and Ico • In cases where Ico (and a) are low 

 when the collector point is initially set down on the treated surface, an 

 increase in Ico and a may be brought about by mechanical motion of the 

 point, (such as "tapping" the manipulator base, or dragging the point 

 across the surface). In other cases the high a and Ico are found immedi- 

 ately after the point is set doAvn on the freshly treated surface, without 

 any such procedure. None of these effects is observed to an appreciable 

 degree on a freshly etched surface without further treatment. 



The effect of zinc chloride-ammonium chloride solder flux on fresh 

 superoxol-etched surfaces was also investigated. In this case, after 

 the etch, the surface was immersed in almost boiling solder flux for about 

 ten minutes. The effect of this surface treatment on the performance of 

 the unformed transistors was entirely similar to the results quoted in 

 connection with the HF treatment. The treatment increased the reverse 

 collector current and average a, and decreased the forward collector 

 current, on the average. Magnitudes of /c(0, —5) as high as 14 ma were 

 observed on surfaces treated in this way. 



