COMBINED MEASUREMENTS ON ETCHED GERMANIUM SURFACES 1039 



It may be seen from the figures that it is the quantity (F — hi X), 

 lather than Y, which appears to be characteristic of the point in the cycle 

 reached. This property of a semiconductor surface, and possible reasons 

 therefore, have often been discussed in the literature." The total range 

 of surface potential is illustrated in Fig. 10, which is drawn to scale, and 

 also shows sundry other points of interest found in the present research. 

 The potential diagrams for n-type and p-type are drawn with the Fermi 

 levels aligned, to show the relation between the property (F — In X) = 

 const, and the frequently observed smallness of the contact potential 

 difference between n and p-type germanium. 



As to the reproducibility and accuracy of the work presented here, 

 the following points may be of interest: (i) The measurements were re- 

 peated on another n-type sample of nearly the same resistivity as the 

 one reported here, but cut from a different crystal. The results on this 

 sample were indistinguishable, within the experimental error, from those 

 found on the first n-type sample, (ii) If the sample was re-etched in pre- 

 cisely the same way as before, and the experiments repeated, the re- 

 sults were in good agreement with those obtained before. However, 

 variations in the etching procedure sometimes gave quite different re- 



X MAXIMUM IN S 



o ZERO OF dv/dcT 



□ INVERSION POINT 



p-TYPE SAMPLE 



n-TYPE SAMPLE 



Fig. 10 — The shapes of the surface space-charge regions for the p-type and 

 /i-type samples in the extremes of gaseous environment. The two surfaces are to 

 the center of the figure. The solid curves show the center of the gap (intrinsic 

 Fermi level) plotted against distance, in units of an intrinsic Debj-e length. Also 

 shown are the positions of the zeros of (dY/dS), the maxima of s, and the minima 

 of surface conductivitj'. 



