246 BELL SYSTEM TECHNICAL JOURNAL 



through the body of the germanium. The early experiments suggested 

 flow along the surface. W. Shockley proposed a modified arrangement in 

 which in effect the emitter and collector are on opposite sides of a thin slab, 

 so that the holes flow directly across through the semi-conductor. Inde- 

 pendently, J. N. Shive made, by grinding and etching, a piece of germanium 

 in the form of a thin flat wedge. ^^ Point contacts were placed directly 

 opposite each other on the two opposite faces where the thickness of the 

 wedge was about .01 cm. A third large area contact w^as made to the base 

 of the wedge. When the two points were connected as emitter and collec- 

 tor, and the collector was electrically formed, transistor action was obtained 

 which was comparable to that found with the original arrangement. There 

 is no doubt that in this case the holes are flowing directly through the n- 

 type germanium from the emitter to the collector. With two points close 

 together on a plane surface holes may flow either through the surface layer 

 or through the body of the semi-conductor. 



Still later, at the suggestion of W. Shockley, J. R. Haynes-" further es- 

 tablished that holes flow into the body of the germanium. A block of 

 germanium was made in the form of a thin slab and large area electrodes 

 were placed at the two ends. Emitter and collector electrodes were placed 

 at variable separations on one face of the slab. The field acting between 

 these electrodes could be varied by passing currents along the length of the 

 slab. The collector was biased in the reverse direction so that a small 

 d-c. current was drawn into the collector. A signal introduced at the 

 emitter in the form of a pulse was detected at a slightly later time in the 

 collector circuit. From the way the time interval, of the order of a few 

 microseconds, depends on the field, the mobility and sign of the carriers 

 were determined. It was found that the carriers are positively charged, 

 and that the mobility is the same as that of holes in bulk germanium (1700 

 cmVvolt sec) . 



These experiments clarify the nature of the excess conductivity observed 

 in the forward direction in high-back-voltage germanium rectifiers which 

 has been investigated by R. Bray, K. Lark-Horovitz, and R. N. Smith^i 

 and by Bray.^^ These authors attributed the excess conductivity to the 

 strong electric field which exists in the vicinity of the point contact. Bray 

 has made direct experimental tests to observe the relation between con- 

 ductivity and field strength. We believe that the excess conductivity 

 arises from holes injected into the germanium at the contact. Holes are 

 introduced because of the nature of the barrier layer rather than as a direct 

 result of the electric field. This has been demonstrated by an experunent 

 of E. J. Ryder and W. Shockley .^^ A thin slab of germanium was cut in 

 the form of a pie-shaped wedge and electrodes placed at the narrow and wide 

 boundaries of the wedge. When a current is passed between the electrodes, 



