Electrical Noise In Semiconductors 



By H. C. MONTGOMERY 



(Manuscript received June 3, 1952) 



Transistors, diodes, and single crystal filaments of germanium have com- 

 mon noise properties: a spectrum varying inversely with frequency, and 

 strong dependence on the biasing current. Theoretical attempts to explain 

 this noise are reviewed briefly. Experiments with single crystal filaments 

 indicate that the noise resides in the behavior of the minority carrier. In 

 one type of experiment, the correlation of noise voltages in adjacent por- 

 tions of a filament is quantitatively related to the lifetime and transit time 

 of minority carrier. In another, the effect of a magnetic field on the noise is 

 found in accord with calculated changes in lifetime of the minority carrier. 



In the development of the transistor it was recognized quite early 

 that electrical noise in the device was considerably in excess of Johnson 

 noise, particularly at low frequencies. Noise having a similar spectrum 

 had been observed many years earlier in microphonic carbon contacts 

 carrying a current, and in copper oxide rectifiers, composition resistors, 

 and crystal diodes. Flicker noise in vacuum tubes appears to be a re- 

 lated phenomenon. A number of attempts have been made to deter- 

 mine the mechanism of production of noise of this sort, but none have 

 been particularly successful. 



In this paper we will first surve}^ the more important characteristics 

 of noise in germanium diodes and transistors. This will be followed by 

 a partial hypothesis as to the nature of the noise mechanism. We will 

 then discuss experimental work on noise in filaments of single crystal 

 germanium carrjnng a dc current. These experiments strongly support 

 the hypothesis, and in fact led to its formulation in the first place. 



I. NOISE IN DIODES AND TRANSISTORS 



There are many similarities in the noise phenomena found in diodes 

 and transistors of both the point contact and junction type. It seems 

 likely that the noise mechanism is similar in all these devices. 



One of the most characteristic features of the noise in such structures 



950 



