rRlSCIPLES or transistor actios 245 



the contact. This theory explains how the change in collector current 

 might l)e as large as but not how it can be larger than the change in emitter 

 current. The fact that the collector current may actually change more 

 than the emitter current is believed to result from an alteration of the space 

 charge in the barrier layer at the collector by the hole current flowing into 

 the junction. The increase in density of space charge and in field strength 

 makes it easier for electrons to llow out from the collector, so that there is 

 an increase in electron current. It is better to think of the hole current 

 from the emitter as modifying the current-voltage characteristic of the 

 collector, rather than as sim{)ly adding to the current flowing to the collector. 



In Section III we discuss the nature of the conductivity in germanium, 

 and in Section I\' the theory' of the current-voltage characteristic of a ger- 

 manium-point contact. In the latter section we attempt to show why the 

 emitter current is composed of carriers of opposite sign to those normally 

 in excess in the body of germanium. Section \' is concerned with some 

 aspects of the theory- of transistor action. A complete quantitative theory 

 is not yet available. 



There is evidence that the rectifying barrier in germanium is internal and 

 occurs at the free surface, independent of the metal contact.^' ^^ The bar- 

 rier contains what Schottky and Spenke^^ call an inversion region; that is a 

 change of conductivity type. The outermost part of the barrier next to 

 the surface is p-tj-pe. The p-type region is xQvy thin, of the order of 

 10~^ cm in thickness, .^n important question is whether there is a sufficient 

 density of holes in this region to provide appreciable lateral conductivity 

 along the surface. Some evidence bearing on this point is described below. 



Transistor action was first discovered on a germanium surface which was 

 subjected to an anodic oxidation treatment in a glycol borate solution after 

 it had been ground and etched in the usual way for diodes. Much of the 

 early work was done on surfaces which were oxidized by heating in air. In 

 both cases the oxide is washed off and plays no direct role. Some of these 

 surfaces were tested for surface conductivity by potential probe tests. 

 Surface conductivities, on a unit area basis, of the order of .0005 to .002 

 mhos were found.- The value of .0005 represents about the lower limit of 

 detection possible by the method used. It is inferred that the observed 

 surface conductivity is that of the p-type layer, although there has been no 

 direct proof of this. In later work it was found that the oxidation treatment 

 is not essential for transistor action. Good transistors can be made with 

 surfaces prepared in the usual way for high-back-voltage rectifiers provided 

 that the collector point is electrically formed. Such surfaces exhibit no 

 measurable surface conductivity. 



One question that may be asked is whether the holes flow from the 

 emitter to the collector mainly in the surface layer or whether they flow 



