POINT-CONTACT TRANSISTOR SURFACE EFFECTS 



805 



ETCHED FOR 1 MINUTE IN 

 IN 0.1% KOH AT 5 MA. 



SAME ETCH FOLLOWED 



BY 1 MINUTE IN 48% HF 



< 



5 



z 

 oi 

 cr 



^ 



DRY Ns" 



ROOM 

 AIR 



''V 



■~9— 



(a) 



Ie(+0.5, 0) 

 BEFORE FORMING 



16 



if) 



_l 



D 



12 



O 8 

 d: 



LJJ 

 CD 



5 4 



D 



z 



D 2 



5 



z 



UJ 



5 



^ 



r' 



-9" 



""V 



(b) 



NUMBER OF FORMING 

 PULSES REQUIRED TO 

 FORM TO Vc(3,-5.5)<2 



0.5 



1.0 



1.5 



2.0 2.5 3.0 3.5 4.0 4.5 

 DAYS AFTER ETCHING 



5.0 



5.5 



6.0 



Fig. 17 — Effect of storage ambient on transistor characteristics — electro- 

 etched surfaces. 



Each point on Fig. 17 represents the average of five units on five differ- 

 ent wafers. 



The difference in the electrical properties of the two surfaces in air 

 already noted in previous sections is observed. In addition an increase 

 in surface recombination is indicated on the HF treated surface by a 

 decrease in the turn-off-time measurement (TOT).* Finally, any influence 

 of ambient on the electrical properties of the two surfaces used is ap- 

 parently small. 



4.2.4 A Statistical Survey Experiment on Transistor Forming 



The experiment described here was designed to check some of the 

 effects noted in earlier sections as well as to investigate possible interac- 

 tions between the germanium surface and various ambients experienced 

 during the processing of point contact units. The experimental design 



* TOT is a nonparametric measurement indicative of the switching speed when 

 used in a specific circuit. 



