CHEMICAL INTERACTIONS AMONG DEFECTS IN Ge AND Si 591 



This section will be closed by indicating how the restriction to systems 

 containing equal numbers of donors and acceptors might be lifted. Thus, 

 suppose Na exceeds No • Then there will be Na — Nd mobile holes main- 

 taining charge neutrality. To a first approximation these will screen the 

 N^ — Nd uncompensated acceptor ions so that the No donors will see 

 effectively only A''!, acceptors. Thus in first approximation r can be com- 

 puted for this system by replacing N in the preceding formulas by Nd • 



Of course it is possible that there will be a further effect. Thus the 

 mobile holes will probably shield some of the compensated acceptors as 

 well. This Avill lead to a further (probably small) reduction in t, over and 

 above that obtained by replacing N by Nd - We shall not go into this 

 in the present paper, because in most of the experiments performed Nd 

 was near Na - In the few^ exceptions the crude correction, suggested 

 above, can be used. 



XI. INVESTIGATION OF ION PAIRING BY DIFFUSION 



Most of the theoretical tools required for the study of ion pairing have 

 now been provided, and attention will be turned to experiments which 



10' 



- 7 



iO 



10-8 



Q 



0,0-9 

 JJ 



UJ 

 CL 



10- 



5 ,n-ii 



10" 



o 10' 

 Q 



■12 



10" 



10" 



10-'5 



o.oot 



TEMPERATURE IN DEGREES KELVIN 

 600 500 400 350 300 250 



200 



0.002 0.003 0.004 0.005 



t/TEMPERATURE IN DEGREES KELVIN 



Fig. 19 — Diffusivitj' of lithium in germanium extrapolated from the data of 

 Fuller and Severiens. 



