SKMfCOXDrCTORS ,U3 



of the germanium. The lH)les iiitrochiced in this way gradually combine with 

 electrons and disappear so that at large distjuices the current consists largely 

 of electrons. Similar effects occur at )i-p boundaries in germanium; the 

 current in the forward direction consists in part of holes flowing from the 

 p-iypo region into the ;/-type region and electrons tlowing from the «-type 

 region into lhc/>-type region. 



The alteration of concentration of carriers and conductivity by current 

 tlow may be used to produce amplification in a number of ways. In the 

 type-A transistor two point contacts are placed in close proximity on the 

 upper face of a small block of ii-iype germanium. A large area low resistance 

 contact on the base is the third element of the triode. Each point, when con- 

 nected separately with the base electrode, has characteristics similar to those 

 of the rectifier. When operated as an amplifier, one point, called the emitter, 

 is biased in the forward direction so that a large i)art of the current consists 

 of holes flowing away from the contact. The second point, called the collector, 

 is biased in the reverse direction. In the absence of the emitter, the current 

 consists largely of electrons flowing from the collector point to the base 

 electrode. When the two points are in close proximity there is a mutual in- 

 fluence which makes amplification possible. The collector current produces 

 a field which attracts the positively charged holes flowing from the emitter, 

 so that a large part of the emitter current flows to the collector and into the 

 collector circuit. 



It has been found that rectifying boundaries between n- and p-type 

 germanium may be used both as emitters and collectors, so that it is possible 

 to make transistors without point contacts. 



The following five papers are concerned with the behaviors of holes and 

 electrons in semiconductors, with particular emphasis upon rectifying junc- 

 tions and transistors. The first paper "Hole Injection in Germanium" de- 

 scribes new experiments on the behavior of holes and shows how their 

 numbers and velocities may be measured and how they may be used to 

 modulate the conductivity in the "filamentary transistor." The second paper 

 "Some Circuit Aspects of the Transistor" describes the characteristics and 

 equivalent circuits for the transistor. "Theory of Transient Phenomena in 

 the Transport of Holes in an Excess Semiconductor" describes in mathe- 

 matical terms a number of the processes encountered in the first paper and 

 brings out interesting features of the nature of an advancing wave front of 

 holes. "The Theory of Rectifier Impedances at High Freciuencies" analyzes 

 the behavior of metal-semiconductor rectifiers for high frequencies for the 

 case in which the current is carried by one type of carrier only. As mentioned 

 above, in rectifiers formed from p-ii junctions, currents of both holes and of 

 electrons must be considered. Such rectifiers and related subjects are dealt 

 with in "The Theory of p-n Junctions in Semiconductors and p-n Junction 

 Transistors." 



