SURFACE PROPERTIES OF GERMANIUM 13 



At times evidence has been obtained to indicate that the dc value changed 

 sign. At other times the dc (Ac.p.)l behaved as if the place where it 

 went through zero was shifted in c.p. from the point where the ac 

 signal goes through zero. In view of this it was necessary to prove that 

 the ac signal was changing phase at the zero point and not just going 

 down in the noise and then increasing again without phase change. This 

 was done by comparing the phase of the signal with a signal from a 

 photocell placed in the same chopped light beam. By this means it was 

 proved conclusively that the ac light signal was actually going through 

 zero. 



Some data were obtained on change of contact potential with light 

 on n-type samples C and E having progressively smaller specific re- 

 sistances. It was found that (Ac.p.)l decreased with specific resistance. 

 It also decreased into the noise as the contact potential was increased, 

 so that it could not be determined if it changed sign as for samples A 

 and D. Because of the smaller signal (Ac.p.)z, could not be measured 

 easily except by the ac method and so far the signal has not been cali- 

 brated properly. 



Some preliminary data on p-type silicon indicate that (Ac.p.)i, for 

 this sample was negative and that it decreased as c.p. was decreased. 

 The magnitude of (Ac.p.)l for the same light intensity was much larger 

 than for germanium and so far it has not been found to go through zero 

 and change sign in the experimental range. 



III. Other methods of varying the c.p. 



In some cases N2 was used in place of O2. A spark discharge in the 

 N2 had very little effect on the c.p. On the other hand wet N2 produced 

 much the same effect as wet O2. The positive extreme in c.p. was about 

 0.1 volt greater in the case of wet N2. After the wet treatment dry N2 

 was not nearly as effective as dry O2 in reducing the c.p. to its inter- 

 mediate value. This can hardly be due to a difference in dryness of the 

 two gases since the same drying column was used in both cases. The 

 results indicate that dry N2 tended to leave the surface in whatever 

 condition obtained before the dry N2 flow was started, and that O2 

 counteracts the effect of H2O. 



With dry N2 as a carrier, other vapors were tried. A. N. Holden sug- 

 gested trying a peroxide and picked out ditertiary butyl peroxide as 

 being reasonably safe. Use of this vapor was found to produce the same 

 changes as the spark coil in the O2 flow. Other vapors having OH radicals 

 such as methyl alcohol and acetic acid were found to act the same way 



