974 THE BELL SYSTEM TECHNICAL JOURXAL, SEPTEMBER 1952 



It is not yet clear whether the noise is a surface or a volume property 

 of the material, but it is well established that the surface properties 

 have an important connection with the magnitude of the noise. From 

 some of the experimental work it seems likely that the generation and 

 recombination processes are separate and have different noise prop- 

 erties. Because of the nonequilibrium situation, this does not violate the 

 principle of detailed balancing. It seems probable that a more complete 

 understanding of the generation and recombination processes and a 

 clearer picture of the origin of noise in semiconductors may be expected 

 to develop together. 



VII. ACKNOWLEDGEMENT 



The analysis leading to the theoretical relations between noise and 

 magnetic field is the work of W. Shockley and H. Suhl, under w^hose di- 

 rection the calculations leading to the curves of Figs. 10-11 were carried 

 out. The continued interest of Dr. Shockley in the experimental work 

 has been invaluable. The author is indebted to many associates for help- 

 ful discussion of certain problems, and also for the construction of many 

 of the devices and materials which entered into the experimental work. 



Appendix 



Suppose that a source of holes located at a point Xo in a filament pro- 

 duces a fluctuating current of holes of rms value Ji in a specified fre- 

 cjuency band. The hole current is swept down the filament by a field E 

 and is assumed to decay exponentially according to the relation 



J = ./ie~^^-'°^/' (1) 



where the life path f may be expressed in terms of drift velocity v, hole 

 mobility ju, and lifetime r 



C = Vt = ijlEt. 



Assuming that the frequency of measurement is low enough to justify 

 neglecting the hole transit time, the noise voltage due to holes from a 

 single source is proportional to the number of holes present in the seg- 

 ment. This is obtained by integrating (1) over an appropriate range 



dv = Ji f e-(^-'«)/' dx 



_ {K.e^'^'^e-" - e-"'] x, < a (2) 



~ |ki[1 - e-^^'°^^'] a < .To < h 



where Kx is an omnibus constant \\hich will cancel out in the final result. 



