262 



BELL SYSTEM TECHNICAL JOURNAL 



when evaluated for room temperature. Thus for «« '^ lO^Vcm', corre- 

 sponding to high-back-voltage germanium, Hh is the order of 10'^. The 

 equilibrium concentration of holes is small. 



Below the intrinsic temperature range, rie is approximately constant and 

 Uh varies as 



nh = {CeCnT^/ue) exp (-Eo/kT). (3.11) 



IV — Theory of the Diode Characteristic 



Characteristics of metal point-germanium contacts include high forward 

 currents, as large as 5 to 10 ma at 1 volt, small reverse currents, correspond- 



-180 -<60 -140 -120 -100 -80 -60 -40 -20 <.0 



APPLIED VOLTAGE 



Fig. 14 — Current-voltage characteristic of high-back-voltage germanium rectifier- 

 Note that the voltage scale in the forward direction has been expanded by a factor of 20. 



ing to resistances as high as one megohm or more at reverse voltages up to 

 30 volts, and the ability to withstand large voltages in the reverse direction 

 without breakdown. A considerable variation of rectifier characteristics 

 is found with changes in preparation and impurity content of the germa- 

 nium, surface treatment, electrical power or forming treatment of the con- 

 tacts, and other factors. 



A typical d-c. characteristic of a germanium rectifier^^ is illustrated in 

 Fig. 14. The forward voltages are indicated on an expanded scale. The 

 forward current at one volt bias is about 3.5 ma and the differential resist- 

 ance is about 200 ohms. The reverse current at 30 volts is about .02 ma 



