HIGH FREQUENCY SEMICONDUCTOR AMPLIFYING DEVICES AND CIRCUITS THEREFOR

1439217 Microwave transistor GENERAL ELECTRIC CO 24 Oct 1973 [25 Oct 1972] 49553/73 Heading H1K The collector region of a microwave-amplifying transistor has an avalanche portion adjacent the collector junction and a uniformly doped drift portion extending from the avalanche portion to the collector electrode. The distance between the collector junction and the collector electrode is chosen to be half the saturation drift velocity of majority carriers in the collector divided by the centre frequency of the band to be amplified, and the net activator concentration is chosen to vary along the length of the collector region such that when it is depleted along its length an electric field is produced therein which produces a finite value of conduction carrier multiplication. The material of this collector region should have an avalanche multiplication factor for the majority carriers therein significantly greater than that for minority carriers. Over a wide range of field intensities, silicon is useful for NPN transistors and germanium for PNP. A silicon transistor is typically operated with a bias such as to give an electron multiplication factor in the range 5-50. The net activator concentrations in emitter, base, avalanche portion and drift portion may typically differ in a decreasing direction by steps of two orders of magnitude. The particular silicon transistor shown has a collector electrode comprising the N + substrate 51 and a gold-antimony ohmic contact 67 thereto. The drift portion of the collector is formed by an N- epitaxial layer 52 in which the avalanche portion 53 is formed by diffusion. The base region 55 and its peripheral guard portion are also formed by diffusion. The emitter regions 56 are formed by diffusion from epitaxially deposited N-type silicon 57 forming portions of the emitter electrodes which are completed by aluminium 58 deposited as a single layer with the base electrodes 61 and separated therefrom by etching. The emitter and base metallization is interdigitated.