268 BELL SYSTEM TECHNICAL JOURNAL 



mal eflfects are unimportant. Electrons flow from the metal point contact 

 to the germanium, and holes flow in the opposite direction. 



Benzer^^ has made a study of the variation of the reverse characteristic 

 with temperature. He divides the current into three components whose 

 relative magnitudes vary among different crystals and which vary in differ- 

 ent ways with temperature. These are: 



(1) A saturation current which arises very rapidly with applied voltage, 

 approaching a constant value at a fraction of a volt. 



(2) A component which increases linearly with the voltage. 



(3) A component which increases more rapidly than linearly with the 

 voltage. 



The first two increase rapidly with increasing temperature, while the 

 third component is more or less independent of ambient temperature. It 

 is the saturation current, and perhaps also the linear component, which are 

 to be identified with the theoretical diode current. 



The third component is the largest in units with low reverse resistance. 

 It is probable that in these units the barrier is not uniform. The largest 

 part of the current, composed of electrons, flows through patches in which 

 the height of the barrier is small. The electrically formed collector in the 

 transistor may have a barrier of this sort. 



Benzer finds that the saturation current predominates in units with high 

 reverse resistance, and that this component varies with temperature as 



/, = -he^'^'^, (4.12) 



with € nearly 0.7 e.v. The negative sign indicates a reverse current. Ac- 

 cording to the diode theory,"*^ one would expect it to vary as 



/. = -BTh'"^'^. (4.13) 



Since e is large, the observed current can be fitted just about as well with 

 the factor 7^ as without. The value of e obtained using (4.13) is about 0.6 

 e.v. The saturation current** at room temperature varies from 10"'^ to 

 10~^ amps, which corresponds to values of B in the range of 0.01 to 0.1 

 amps/deg^. 



The theoretical value of B is 120 times the contact area, Ac. Taking 

 A c '^ 10~^ cm^ as a typical value for the area of a point contact gives B '^ 

 10-* amps/deg2 ^hich is only about 1/100 to 1/1000 of the observed. It 

 is difficult to reconcile the magnitude of the observed current with the large 

 temperature coefficient, and it is possible that an important part of the total 

 flow is a current of holes into the contact. Such a current particularly is 

 to be expected on surfaces which exhibit an appreciable surface conductiv- 

 ity- 



Neglecting surface effects for the moment, an estimate of the saturation 



