HOT ELECTRONS m GERMANIUM AND OHM*S LAW 



995 



large ends. Since the fields at the large ends are small, carrier injection is 

 largely suppressed; furthermore, the electric fields are applied for such a 

 short time during the pulse that, even if holes were injected at one of the 

 ends, they would not have time to reach the narrow section of the bridge 

 and modulate its conductivity during the period of the pulse. 



Further causes of non-linearity can arise from inhomogeneities in the 

 germanium material itself. For example grain boundaries in polycrystalline 

 germanium are known to have added electrical resistance. Difficulties due 



?0 30 40 60 80 100 200 400 600 1000 2000 4000 10,000 



ELECTRIC FIELD IN THIN SECTION IN VOLTS PER CENTIMETER 



Fig. 2 — Currents and estimated drift velocities deduced from E. J. Ryder's pulse data 

 on a specimen of »-type germanium of 2.7 ohm-cm resistivity. [The fact that the numeri- 

 cal values of current density and drift velocity have the same digits is a consequence of 

 the accident that <r = 1/2.7 = 0.37 is almost exactly 10"^ times the mobility.] 



to inhomogeneity have largely been eliminated in these experiments by 

 the use of highly homogeneous single-crystal germanium material fur- 

 nished by G. K. Teal and his collaborators. 



Other experimental precautions are necessary, such as assuring a smooth 

 poHshed surface on the filament; if this is not done, apparently holes are 

 injected from the surface irregularities of the thin section between the 

 large ends. It is also necessary to make corrections for end effects since 

 some of the resistance arises within the large blocks themselves. 



Some of the data obtained by Ryder are shown in Fig. 2. The drift ve- 

 locity, plotted as ordinate, is not measured directly but is inferred from 

 the measured currents through the specimen by the following reasoning: 



