CHEMICAL INTERACTIONS AMONG DEFECTS IN Ge AND Si 611 



8 



5 



V 



z 

 o 



< 



a: 



O 



I 



10' 



10 



13 



0.1 



0.2 0.3 0.4 0.5 0.6 



1/ TEMPERATURE IN DEGREES KELVIN 



0.7 



0.8 



Fig. 29 — Plot of hole concentration as a function of reciprocal temperature for 

 a sample containing ion pairs. 



An even more striking result appears. From the above results the 

 density of lithium atoms involved in pairs is 8.85 X 10^^ cm~^ — 2.6 X 

 10 cm~ = 8.6 X 10 cm~ , the same number by which the density of 

 acceptors has been decreased! There can be little question that ion pairing 

 is the mechanism responsible for the removal of states. 



In closing it is worth pointing out that the density of unpaned lithiums 

 2.6 X 10 cm~ , is certainly not characteristic of the low temperatures 

 at which the above Hall measurements were performed. Obviously a 

 density characteristic of some higher temperature has been quenched 

 into the specimen. At the low temperature involved the unpaired density 

 would be effectively zero. 



XV. RESEARCH POSSIBILITIES 



The fields described in the preceding text have been hardly touched, 

 even by this long paper, and it does not seem fitting to close without 

 some speculation concerning the possibilities of future work. 



In the first place, there are other donors and acceptors besides lithium 

 which are reasonably mobile in germanium or silicon, e.g. copper, iron, 



