CHEMICAL INTERACTIONS AMONG DEFECTS IN Ge AND Si 559 



Curve A possesses a maximum (just as the Dq^ curve of Fig. 5) in the 

 neighborhood of 650°C. A marked disparity is apparent between solu- 

 bihties in undoped and doped sihcon, the sohibiHty in the latter bemg 

 greater. Below 500°C this disparity is easily understood. It stems from 

 the electron-hole equilibrium considered previously. However the high 

 solubility in doped silicon at high temperatures is not explicable on this 

 basis since the crystal becomes intrinsic, and e'^e~ is mostly dissociated. 

 To account for this phenomenon Reiss, Fuller, and Pietruszkiewicz 

 invoked the idea of interaction between Li'^ and B". They presented 

 the following argument. 



At low temperatures lithium ions occupy the interstices of the silicon 



200 



400 600 800 1000 



TEMPERATURE IN DEGREES CENTIGRADE 



1200 



Fig. — Plots showing the soluliilitj' of lithium in silicon us a function of tem- 

 perature. The external phase is an alloy of lithium and silicon. Curve A is for un- 

 doped silicon. The locus of the points in B is for silicon doped with about 1.9 X 10^* 

 cm~^ boron. 



