COMBINED MEASUREMENTS ON ETCHED GERMANIUM SURFACES 1035 



From Fig. 5 one may now calculate* the changes occurring in Xs , 

 the (reduced) charge in fast states, since Fp — r„ may be read from 

 Tables V and VI, and Ss - S - (f^ - f,). Fig. 6 shows (d2s/dY)i 

 as a function of 1" — In X, calculated from the experimental results in 

 this way. [The reason for plotting against Y — In X instead of Y is that 

 this quantity represents the difference, in imits of (kT/e), between the 

 electrostatic potential at the surface and the Fermi level. In this way the 

 effects of difference from sample to sample in the position of the Fermi 

 level in the interior are eliminated.] Notice that the measurements of 

 {dT^s/dY)s for the two samples have the same general shape, and that 

 the turning points of the two curves occur at about the same value of 



dY 



-30 



Fig. 6 — Differential charge in fast states versus surface potential. The graphs 

 show {dZs/dY) plotted against F — In X. Dots: p-type; circles: n-type. Atypical 

 result of Brown and Montgomery, using 28 ohm-cm p-type germanium, is also 

 shown. 



