36 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



recombination. The results of Fig. 6 indicate that this change in trap 

 distribution also has been in a direction to increase ( — Fb). This is what 

 one would expect if Nb has increased with respect to A^o , ie., sand-blasting 

 increases the effective number of acceptor traps. About all that can be said 

 about the rest of the results in Fig. 6 is that if one knew the surface trap 

 structure in number and energy distribution for the etched surface then 

 one could deduce from the results in Fig. 6 the distribution of traps for the 

 sand-blasted surface over part of the energy range at least. 



The theory developed here for the germanium surface may not apply 

 at all for a silicon surface. In a previous discussion of the silicon surface 

 it was assumed that the resistance to surface trapping occurred mainly 

 in the flow across the space charge layer rather than from the surface 

 to the traps. This may well be the case in silicon. An investigation of the 

 silicon surface using these same techniques should clarify this point. 



It should be emphasized that the ambient used for this study and the 

 variations in it are special in that they do not necessarily correspond to 

 the atmosphere of ordinary room air. It is very probable that constituents 

 in room air other than oxygen ions and water vapor are important, such 

 as salt ions for instance. It is quite probable that Vs for such a surface 

 exposed to room air would increase considerably with time instead of 

 staying relatively constant as it does under the bell jar. 



CONCLUSIONS 



A method has been developed for studying the surface properties of 

 Ge in a gaseous ambient at atmospheric pressure. It has been found 

 that the Ge surface interacts with this ambient. Two atmospheric 

 constituents that are important in this interaction, oxygen and vapors 

 with OH radicals, have been isolated. With the controlled use of these, 

 the surface dipole of Ge can be cycled between two extremes. Thus the 

 dependence of other properties of the Ge surface on surface dipole, such 

 as change of contact potential with illumination and surface recombina- 

 tion, can be determined. 



It is evident from the results that the method is very powerful. In 

 order to complete the present study, it was necessary to stop trying new 

 experiments since almost all directions of variation open up new and 

 interesting phenomena. These results on Ge are really just a beginning, 

 and the preliminary data on silicon indicate that the same method would 

 also be fruitful on other semiconductors. The technique is of course not 

 limited to atmospheric pressure. 



A tentative theory of the Ge surface has been developed that is 

 suflficient to explain the experimental results on a semi-quantitative 

 basis. Theory and the experiment together predict approximately the 



