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BELL SYSTEM TECHNICAL JOURNAL 



In Fig. 7 we show a plot, obtained in this way, from a sample of germa- 

 nium having dimensions 1.0 X .05 X .08 cm. It is seen that the increase in 

 collector current due to hole arrival decays exponentially with a time con- 

 stant of 18 microseconds. This time constant increases as the dimensions 

 of the germanium sample are increased so that a time constant of 140 micro- 

 seconds was measured, using a sample having dimensions 2.5 X .55 X .50 



a 13 



O 



0.3 0.4 0.5 0.6 0.7 

 HOLE DENSITY IN TERMS OF p/n^ 



Fig. 6 — Conduclance of P\ and Pi of Fig. 3 in series as a function (;f p!n» , showing that 



conductance depends on hcle concentration but not on currents in filament. For 



each value of /< the hole density was varied hv varying h + /< from .038 to 



0.78 ma. 



cm. Since the holes injected into the interior of this sample can diffuse to 

 the surface and recombine in about 100 microseconds, the process may still 

 be largely one of surface recombination. In any event, it may be concluded 

 that the lifetime in the bulk material used must be at least 140 microseconds. 

 Making use of the electron density determined from other measurements, 

 we conclude that the recombination cross section must be less than 10 

 cm-. This cross section, which is less than 1 400 the area of a germanium 



