POINT-CONTACT TRANSISTOR SURFACE EFFECTS 797 



manipvilator units could be made with no difficulty, the same material 

 fabricated into a completed structure showed completely different char- 

 acteristics. In the course of investigation of this problem, it was ofund 

 that the nature of the germanium surface treatment and specifically 

 treatments calculated to produce or react with germanium oxide can 

 profoundly affect the "formability" of the germanium surface as well 

 as a number of other transistor parameters in the fabricated units. 



It is the purpose of this section to emphasize the importance of con- 

 sidering the surface properties of germanium in attempting to solve such 

 specific problems of development encountered in devices of this type. 

 In particular, the striking variability of transistor forming on etched 

 germanium surfaces subjected to varying chemical treatments and am- 

 bients will be described, as well as the effects of such pre-forming treat- 

 ments on the parameters of the finished units. The experiments discussed 

 in the previous section indicate how changes in the double layer at the 

 germanium surface can influence the characteristics of an unformed 

 point diode. In turn, the experiments below indicate how the character- 

 istics of the unformed diode are related to the device properties of the 

 transistor collector produced by forming the diode. 



4.2 Experimental Results 



4.2.1 Pilot Process Forming Yields 



The forming yield of a point-contact transistor is determined by the 



\'alues of the acceptance criteria and the allowable limits for each of these. 



Often, different criteria as well as different forming techniques are used 



j for different transistors, so that direct comparison of results is quite 



I 



complex. There are, however, certain common requirements placed on 

 all point-contact transistors: 



(a) The unit is formed so that the average alpha is roughly two or 

 more. The collector current at a relatively high emitter current and low 



! collector voltage is usually an approximate measure of this value, 

 /c(6, —5) for example. 



(b) The collector current with no emitter current flowing should be 

 as low as is commensurate with the first objective. 



The other transistor parameters are either directly or indirectly re- 

 lated to these. The number of pulses required to achieve the minimum 

 forming objective, therefore, is one direct measure of the formability of 

 a particular transistor; the average alpha obtained after pulsing is an- 

 other. However, one must consider both average alpha and Ico , since 

 \\ hile forming to a given average alpha, the Ico may increase prohibi- 



