iioi.ii iwiEcrios i.\ c;F.R\iA.\ir \f 



355 



concentraticju throughout the entire cross section; the hole concentration 

 may be much less near the surface due to recombination on the surface. 

 Techniques of the sort described above can be used to measure the })roi)- 

 erties of collector points. If a collector ])oint is placed l)et\veen the emitter 

 and 7^ in Fig. >■?, then the hole current extracted by the collector can be 

 determined in terms of the hole current past I\ and 7^. . By these means an 

 "intrinsic a" for the collector point can be determined. The intrinsic a is 



0.04 0.06 0.08 0.10 0.12 0. 

 HOLE DENSITY IN TERMS OF p/p 



0.16 0.18 



Fig. 5 — Dependence of collector current Ic upon average hole density being swcj)! \>y 

 collector point. Collector biased 20 volts reverse. 



defined as the ratio of change in collector current per unit change in hole 

 current actually arriving at the collector. 



4. Studies of Tr.ansiext Piienomen.\ 



'I'he technique of using a collector point to measure hole concentrations 

 has been employed in a number of experiments similar to those described in 

 connection with Fig. 1. These experiments give information concerning 

 hole lifetimes, hole mobilities, diffusion and conductivity modulation. 



One of the methods employed to measure hole lifetime involves the meas- 

 urement of the increase in collector current, produced by the arrival of the 

 leading edge of the hole pulse, as a function of the transit time of the holes 

 from emitter to collector. This time is varied by varying the distance be- 

 tween the emitter and the collector jxjints. 



