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TEH BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



Table VIII 



oxides which are present so that a good solder joint may be made. Since 

 the oxide on chemically-etched germanium is likely of the soluble form, 

 one might assume that the results of Table VII imply that the action 

 of the flux and heat tends to dissolve or remove this layer. Also implied 

 by the data is that the presence of such an oxide layer is essential to 

 efficient forming. 



The experiments summarized in Table VIII further substantiate this 

 hypothesis. These data represent manipulator transistors made on the 

 same germanium wafers which had been treated in succession to a normal 

 superoxol etch, a treatment in 48 per cent hydrofluoric acid, and a treat- 

 ment in hydrogen peroxide, superoxol strength. Since the soluble form 



of germanium dioxide is known to react with hydrofluoric acid, it is 

 presumed that the action of the HF is to partially or wholly remove any 

 oxide left by the etch. The H2O2 tends to restore the original surface 

 conditions left by the etch. Each figure represents the average of five 

 transistors formed to the 2N21 acceptance criterion, (Vc(S, —5.5) ^ 

 2.0 volts). 



In this case the hydrogen peroxide treated units have an extremely 

 high average alpha, but the Ico is also higher than for normally etched 

 units. In terms of the device properties, a unit with a more or less typical 

 average alpha with a low Ico is more desirable than the one Avith an 

 extremely high average alpha but accompanying high Ico • It has not 

 been determined whether the Ico would be lower for the superoxol treated 

 units if it had been possible to form to the same average alpha as the 

 normally etched units. This is an important piece of device design in- 

 formation which is currently under investigation. 



It is clear from these experiments that the nature of the germanium 

 surface, and most probably the nature of the germanium oxide layer on 

 it, to a large extent, determines the properties of the transistor formed 

 on this surface. Direct application of this knowledge to the fabrication 

 process of the hermetically sealed point contact transistor has been 

 carried out by N. P. Burcham. 



