SURFACE PROPERTIES OF GERMANIUM 



9 



5 where one cycle each is plotted for both sample A and D, for each of the 

 two surface treatments, sandblasting and etching. The curves are approxi- 

 mately all of the same shape so that the differences between them can be 

 described by giving the shift in contact potential necessary to superimpose 

 the curves. This treatment works very well except for the first part of the 

 cycle after the spark coil where the shift necessary is sometimes more and 

 sometimes less than that needed to make all of two curves superimpose well. 

 Note in Fig. 5 that the contact potential for sample A etched is always 

 greater than for sample D etched. In the case of the sandblasted surface 

 just the reverse is true. Also the contact potential for the etched surface of 

 either sample is always larger than for the sandblasted. 



Using these methods comparable results were obtained on two other 

 n-type samples, C and E, of increasingly lower specific resistance. 

 Taking advantage of the relation between carrier concentration and 

 the position of the Fermi level we have plotted in Fig. 6, the contact 

 potential for both the etched and the sandblasted surfaces versus the 

 position of the Fermi level (Ep — Ei) in electron volts. The contact 

 potential values used were taken from the saturation values in wet O2 

 but the shapes of the curves w^ould be much the same for any other 

 point in the cycle. The contact potentials are thought to be accurate 

 to about 0.01 volts. Solid lines have been drawn through the points. 

 Note that the contact potential for the etched surface is always greater 

 than for the sandblasted surface, i.e., the work function is always less 

 and that this difference is greater when Ep = Ei or the germanium is 

 nearly intrinsic. 



20 24 28 32 

 TIME IN MINUTES 



Fig. 5 — Comparison of cycles for samples A and D with sandblasted and 

 etched surfaces. 



