A Germanium N-P-N Alloy Junction Transistor

Abstract

This paper describes a germanium n-p-n alloy junction transistor which is the counterpart to the germanium p-n-p junction transistor previously described. The importance of this new device arises from a fundamental difference between the two types. In the p-n-p transistor the active charge carriers are positive "holes"; in the n-p-n transistor the active charge carriers are negative electrons. Because these devices operate from power sources of opposite polarity, the two types may be advantageously combined in special circuits to eliminate components and fulfill unusual requirements. Because the electron mobility is more than twice that of holes, one of the factors affecting high-frequency response is more favorable for the n-p-n transistor than for its p-n-p counterpart. This n-p-n junction transistor is made by fusing a binary leadantimony alloy into each of the two opposite faces of a thin wafer of p-type single-crystal germanium. Since this alloy is ductile, the electrodes may be made relatively large if desired, as there is less danger of introducing differential expansion strains. The techniques and processes of assembly are similar to those employed for p-n-p junction transistors by the alloy process. However, a difference arises from the more uniform penetration afforded by the binary alloy. This leads to more planar junctions and permits better control of junction spacing. Distribution curves on a typical lot of 100 units are given; best power gain was 45 db, "alpha" 0.997 and 1-kc noise factor, 3 db. High "alpha" is maintained as the collector current is increased.