The base width of a transistor is an important factor affecting the cut-off frequency, current gain and maximum collector voltage. The paper is concerned with the manner in which wafer thickness, size of indium dots, alloying temperature, flatness of junction, furnace atmosphere and junction area affect the limits that can be achieved in the alloying process.(1) INTRODUCTION Fn order to examine the problems involved in the making of low-power (up to lOOmW) germanium p-n-p alloy-junction transistors, a number of experimental transistors have been made. Two of the most important of the electrical parameters of the transistor are the current gain, hf e , and the cut-off frequency, fa., and for these to have large values the distance W between the emitter and collector junctions must be small. Theoretically with small emitter current density and a base of uniform resistivity, a cut-off frequency greater than 15Mc/s requires a base width of less than IOJU. To achieve an effective spacing of this value without risk of local punch-through it is essential that the emitter and collector junctions are flat and parallel. A further requirement is that the /?-type germanium redeposited on cooling after alloying should be adequately thick and of suitable resistivity and lifetime. Consequently, the main part of the investigation has been to establish what is necessary in the alloying procedure to produce flat junctions and uniform redeposition.(2) MATERIALS USED The resistivity, p, and the lifetime, T, of the n-type germanium are two of the factors that determine the electrical characteristics of the transistor. The value of the collector-to-base breakdown voltage due to avalanche effect, V a , is approximately proportional to resistivity, 1 but collector-to-emitter punch-through voltage, V p , is proportional to W 2 lp. To ensure that the maximum collector voltage is as large as possible for the base width required, the resistivity should be chosen so that V a and V p are approximately equal. In addition, for small values of collectorto-base leakage current, I cb0 , and base series resistance, r bs , a small resistivity is required. The minority carrier lifetime must not be too small if an acceptable current gain is to be achieved. 2

An electrostatic analyzer has been built for use with the high pressure electrostatic generator at the University of Wisconsin. The proton beam from the generator is deflected through a 90° arc of 40″ radius by means of a radial electric field between curved metal plates spaced 516′′ apart. Suitably disposed slits select a beam which has a very small energy spread. The apparatus has been operated with energy resolutions up to 5000, and preliminary tests have been made, using the 985- and 1020-kv γ-ray resonances in the reaction Al27+H1→Si28+hν.

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