Optimum design of electron beam-semiconductor linear low-pass amplifiers—Part II: Output capabilities

This paper presents a simplest case analysis of the peak quasi-static output capability of a linear lumped-target beam-semiconductor amplifier. The basic assumptions in the response analysis of Part I [1] are used, together with the premise that the semiconductor velocity-field characteristic exhibits strong saturation at fields well below avalanche breakdown. The analysis applies to the ultimate pulsed output at low duty cycle since thermal effects are not considered. The fundamental current and voltage limitations on target output are discussed separately in limiting cases, and it is shown that the linear output capability is determined jointly by the drift-region width, bias field profile, and avalanche multiplication constraint. The dynamic electric field behavior is calculated for the general case where voltage and current effects appear simultaneously, and it is shown how the output capability can be maximized for a given target area and load impedance by proper choice of drift-region width and doping level. The ultimate pulsed dc output current, voltage, and power levels are evaluated for semiconductor targets in terms of the target area, load impedance, carrier drift velocity, semiconductor band gap, and avalanche multiplication constraint. Detailed numerical predictions are given for silicon targets. The usefulness of the quasi, static analysis is discussed, and it is shown that the results obtained apply with minor modification to the case of step-function excitation. In conjunction with the results of Part I, the combined gain, rise time, and pulsed output power performance boundaries are established for the basic lumped-target beam-semiconductor amplifier. The feasibility of a subnanosecond-rise-time linear amplifier with 50-dB gain and a multikilowatt pulsed output level is shown. Various semiconductor materials are evaluated for application in a beam-semiconductor amplifier by examination of an overall figure of merit comprising gain, rise time, and peak output capability, and it is demonstrated that Si, Ge, and GaAs are nearly equal in overall merit. In conclusion, several novel devices are described that illustrate the adaptability of the electron beam-semiconductor concept to multiple-signal amplifiers, fast waveform sampling, and traveling-w- ave amplification.