Theory of Magnetic Effects on the Noise in 

 a Germanium Filament 



By HARRY SUHL 



(Manuscript received October 10, 1952) 



A magnetic field will influence the current noise in a germanium fila- 

 ment. This fact hears out the hypothesis that at least part of the noise arises 

 from minority carriers emitted in random hursts and recomhining at the 

 surfaces. A quantitative theory of this effect is given. 



INTRODUCTION 



In a series of fundamental experiments, H. C. Montgomery^ has es- 

 tablished that minority carriers play an important part in the current- 

 noise associated with semiconductors. He found that on the one hand, 

 the noise voltage is usually proportional to the biasing current, suggest- 

 ing fluctuations in the conductivity, and hence the carrier concentration. 

 On the other hand the spectrum of the noise suggested a rather coarse- 

 grained time variation, not likely to be caused by fluctuations in the 

 normal carrier density. One might conclude, therefore, that the noise 

 is caused by a distribution of sources emitting or absorbing minority 

 carriers in random bursts. Such carriers would be subject to the same 

 laws of motion and of recombination as intentionally injected carriers. 

 Montgomery was, in fact, able to verify that the noise along a filament 

 showed marked correlation over a distance roughly equal to that through 

 which minority carriers could drift in the biasing field before recom- 

 bination. 



W. Shockley has pointed out another corollary of this theory: A mag- 

 netic field transverse to the filament should have a pronounced effect 

 on the noise. This conclusion, too, Montgomery was able to verify 

 experimentally.^ His results are in good qualitative agreement with 

 theory. Complete quantitative agreement was perhaps not to be ex- 

 pected, since technical difficulties prevented attainment of the idealized 

 conditions assumed by the theory. This paper gives an account of that 



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