POINT-CONTACT TRANSISTOR SURFACE EFFECTS 



789 



3.3.2 Unformed Transistors on CPi-Etched Surfaces 



With reference to unformed point contact properties, the CP4-etched 

 surface is not at all similar to the superoxol etched surface. If two beryl- 

 lium-copper points are put down on a ground surface freshly etched; in 

 CP4 , and operated as a transistor, high values of 7c(0, — 10) and 

 /<.(6, —5) are often encountered. However, after an hour or so in room 

 air, both these parameters decrease and after an overnight exposure to 

 room air, the properties of the surface with regard to the transistor ac- 

 tion resemble those of a surface freshly etched in superoxol. At this point, 

 a treatment in 24 per cent HF will return /c(0, —10) and 7c(6, —5) to 

 their originally high values. These effects are summarized in Table IV. 



3.3.3 Diode Characteristics on Electro-Etched Surfaces 



It has been found that the rectification properties of unformed point 

 diodes may also be changed conveniently by changing the conditions 

 during an electrolytic etch in KOH solution. These results are summa- 

 rized in Table V which represents typical variation in reverse current, 

 Ir , with surface variation attainable by adjusting the current density 

 and etching time. In each case the measurements represent data taken 

 on germanium cut from adjacent sections of the same ingot and given 

 the surface treatment noted in the table. In general the electro-etched 

 and chemically etched results agree; that is, any treatment which ap- 

 pears most likely to leave an oxide film (such as the use of a high current 

 density during electro-etching) will yield a diode with improved rectifica- 

 tion characteristics. 



I 3.3.4 Output Characteristic Anomalies 



In the process of examining these chemically treated surfaces, some 

 i of the superoxol-etched n-germanium surfaces were given additional 



Table IV 



