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THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



several velocities of propagation for any specified direction of propagation 

 and frequency. It is to be hoped that more detailed analyses of the data ob- 

 tained by Ryder, together with quantitative interpretations of certain ob- 

 servations of magnetoresistance, may lead to a unique evaluation of the 

 ''refractive constants" of the medium for the electron waves; this possibility 

 is discussed briefly in Section 5. The phenomena in the Zener current range 

 afford another new opportunity to study electron waves in crystals. The 

 waves involved in this effect are those with energies in the energy gap be- 

 tween the conduction band and the valence band; waves in this range have 

 received little attention from either the experimental or theoretical side. 



2. E. J. Ryder's Results 



One of germanium's most noted attributes is its abihty to give am- 

 plification of electrical signals when made into a transistor. The basic phe- 

 nomenon for many types of transistors is that of "carrier injection." As is 



PULSER 



T 



X 



Fig. 1— The principles of E. J. Ryder's technique for observing conductivity in high 

 electric fields. 



well known, germanium may carry current either by the electron mecha- 

 nism in which case it is called w-type germanium, or by the mechanism of 

 hole conduction in which case it is called ^-type. If a suitably prepared 

 electrode is placed on an w-type specimen and current is caused to flow in 

 the sense that removes electrons from the specimen, then the process may 

 cause "hole injection." In this case in addition to removing conduction 

 electrons from the germanium, electrons are removed from the valence 

 bonds so that holes are injected. This leads to nonlinear effects because, 

 as the current passes through the specimen, the number of carriers in the 

 specimen changes and so does its resistivity. 



In order to avoid the secondary deviations from Ohm's law due to carrier 

 injection, Ryder has designed specimens of the form shown in Fig. 1. These 

 specimens have large ends to which the metal electrodes are attached. The 

 resistance arises chiefly from a thin section of the material connecting the 



