Pulse Amplification Using Impact Ionization in Germanium

Some aspects of the phenomena of impact ionization in an impurity doped semiconductor at 4.2°K are described. The ionization time is shown to be a strong inverse function of the electric field. Control of the breakdown process is used to obtain pulse amplification in the millimicrosecond range, using two- and three-terminal devices. These devices are inherently stable, very simply constructed (requiring only ohmic contacts), and have easily manageable dimensions. In controlling the breakdown process, a small amount of control power or energy applied at an early time determines the course of an avalanche-type buildup so that at a later time a substantial change in power or energy level is affected. Although other rise time control amplifiers are known (e.g., the super-regenerative vacuum tube amplifier), the present amplifier is believed to be the first solid state device which operates on this principle. Peak power and current gains on the order of 20 have been obtained for 25 and 50 mμsec pulses. It also appears that voltage gain is possible under somewhat different operating conditions than have been examined to date. The lower limit for pulse length in these experiments was determined by measurement equipment limitations rather than by any device limitation.