PHOTOTRANSISTOR

Under the name “transistor” there have become known crystalline germanium triodes, with the aid of which it is possible to amplify small alternating currents1.

It is known that a transistor consists essentially of a small germanium crystal, to which, at a short distance from one another, two points are brought. The voltage to be amplified is applied to the emitter—a point weakly positively charged relative to the base. The amplified voltage is taken from the collector—a point strongly negatively charged relative to the base.

At the present time a new variety of transistor is being developed, the so-called phototransistor—a very sensitive device that converts light oscillations into electrical ones2. As follows from

a brief journal note, among the merits of the phototransistor, with which great expectations are associated, are its high sensitivity in the visible region of the spectrum, small dimensions, and low inertia (even at a frequency of 20,000 cycles the light oscillations were converted into electrical ones without distortion).

The construction of the phototransistor does not differ from that of known light detectors and resembles an ordinary transistor. The difference from the transistor consists mainly in the absence of an emitter, which is quite understandable if one takes into account that the current in the collector circuit must be controlled by the radiation incident on the crystal, and not by the current in the emitter circuit.

The contact point of the collector rests against the crystal at the site of an indentation. The thickness of the crystal here is equal to approximately one tenth of a millimeter. Light falls on the crystal from the side opposite the collector. The circuit for connecting the phototransistor is given in the figure. The voltage drop across the resistance \(R\) is measured.

V. Bredel

CITED LITERATURE

1. V. S. Vavilov, UFN 40, 120 (1950).
2. Electronics 23, 122, July (1950).