16 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



600 

 500 



400 

 300 



200 



100 

 60 



60 

 50 

 40 



30 



20 



12 



20 24 28 32 

 TIME IN MINUTES 



36 



40 



46 



52 



Fig. 11 — Dependence of the velocity of recombination, y« , on the contact 

 potential cycles. 



biguously. It may well be impossible to do this in Bridgman's operational 

 sense. Most physicists would agree that the Pt reference electrode 

 probably has a work function of around 5 to 7 volts under these con- 

 ditions, but this of course does not help much. 



IV. Measurement of surface recomhination velocity Va 



At first we tried various methods of measuring Va on the Ge surface 

 at the same time that c.p. and (Ac.p.)l were measured. No method 

 was found that could be trusted. As the study progressed we realized 

 that the c.p. of a Ge surface could be cycled in a reproducible way. 

 Since the proper geometry for measuring Vg was a rod or filament,^ 

 rods were prepared of samples A and D with the same chemical surface 

 treatment. The decay of hole electron pairs, created by a point light 

 source, was measured as a function of distance from the light. If the 

 body life time t and the dimensions of the filament are known one can 

 then determine v, . These measurements were made while the gaseous 

 ambient was cycled in the same manner as before. The results for fila- 

 ments cut from samples A and D are plotted against time in Fig. 11. 

 The ambient atmosphere was changed as a function of time just as it 

 was in Figs. 2 to 4. The main conclusion is that within the accuracy of 

 this experiment there is no evident dependence of v, on the changes in 



