PRINCIPLES OF TRAXSfSPOR ACTION 247 



the field strength is large at the narrow end of the wedge and small near 

 the o[)posite electrode. An excess conductivity was observed when the 

 nariow end was made j)ositive; none when the wide end was positive. 

 The magnitude of the current flow was the same in both cases. Holes 

 injected at the narrow end lower the resistivity in the region which con- 

 tributes most to the over-all resistance. When the current is in the oppo- 

 site direction, any holes injected enter in a region of low field and do not 

 have sufficient life-time to be drawn down to the narrow end and so do not 

 alter the resistance ver\^ much. With some surface treatments, the excess 

 conductivity resulting from hole injection may be enhanced by a surface 

 conductivity as discussed above. 



The experimental procedure used during the present investigation is of 

 interest. Current voltage characteristics of a given point contact were 

 displayed on a d-c. oscilloscope.-^ The change or modulation of this char- 

 acteristic produced by a signal impressed on a neighboring electrode or 

 point contact could be easily observ^ed. Since the input impedance of the 

 scope was 10 megohms and the gain of the amplifiers such that the lower 

 limit of sensitivity was of the order of a millivolt, the oscilloscope was 

 also used as a xers' high impedance voltmeter for probe measurements. 

 Means were included for matching the potential to be measured with an 

 adjustable d-c. potential the value of which could be read on a meter. A 

 micromanipulator designed by W. L. Bond was used to adjust the positions 

 of the contact points. 



II — Some Transistor Ch.\racteristics 



The static characteristics of the transistor are completely specified by 

 four variables which may be taken as the emitter and collector currents, 

 le and Ic, and the corresponding voltages, Ve and Vc. As shown in the 

 schematic diagram of Fig. 1, the conventional directions for current flow 

 are taken as positive into the germanium and the terminal voltages are 

 relative to the base electrode. Thus /« and Ve are normally positive, 

 Ic and Vc negative. 



There is a functional relation between the four variables such that if 

 two are specified the other two are determined. Any pair may be taken as 

 the independent variables. As the transistor is essentially a current 

 operated device, it is more in accord with the physics involved to choose the 

 currents rather than the voltages. All fields in the semi-conductor outside 

 of the space charge regions immediately surrounding the point contacts are 

 determined by the currents, and it is the current flowing from the emitter 

 which controls the current voltage characteristic of the collector. The 

 voltages are single-valued functions of the currents but, because of inherent 

 feedback, the currents may be double-valued functions of the voltages. 



