SUKPACE PKOPERTIFS OP GERMANIUM 41 



The values of RnB and Rps relative to Rnt and Rpt are: 



Rns/Rnt = SntVt (A.26) 



Rps/Rpt = Sj,tnt. (A.27) 



In our experiments these are always small compared with unity, since 

 the trapping cross-sections are of the order of 10"^^ cm^ and p< and n« 

 are always less than Nt , which is of the order of lO^Vcm^ 



Barrier resistances may be important for surfaces with a large number 

 of surface traps. Analysis of earlier data on the change of the contact 

 potential of silicon with light was made on the assumption that the 

 probability that an electron or hole reaching the surface be trapped is 

 relatively large, and that consequently the barrier resistances are large 

 compared with the trapping resistances. The present experiments on 

 germanium throw doubt on this interpretation, but further experiments 

 are required to clarify the situation. 



REFERENCES 



1. Bardeen, J., Phys. Rev., 71, p. 717, 1947. Brattain, W. H., Phys. Rev., 72, 



p. 345, 1947 and Semi-Conducting Materials Butterworths Scientific Publica- 

 tions Ltd., pp. 37-46, 1951. 



2. Shockley, W., Electrons and Holes in Semiconductors. D. Van Nostrand, pp. 



318-325, 1950. 



3. Pearson, G. L., unpublished data. J. R. Haynes and W. Shockley, Phys. Rev. 



81, p. 835, 1951. 



4. The CP-4 etch is due to R. D. Heidenreich. The formula is given in Phys. Rev., 



81, p. 838, 1951. This method of treating a Ge surface is due to C. S. Fuller. 



5. C. S. Fuller suggested the use of these fumes. 



6. Goucher, F. S., G. L. Pearson, M. Sparks, G. K. Teal and W. Shockley, Phys. 



Rev. 81, p. 637, 1951. 



7. Shockley, W. and W. T. Read, Phys. Rev., 87, p. 835, 1952. 



8. van Roosbroeck, W., Bell Sys. Tech. Jl., 29, p. 560, 1950. 



