Aluminum-silicon Schottky barriers as semiconductor targets for EBS devices

Abstract

The ideal semiconductor target for EBS devices is most closely approximated by the Schottky barrier junction, with Al having the highest figure of merit. Accordingly, large area (1·27 mm 2), high-field Al nSi Schottky barrier junctions surrounded by a p- n junction guard-ring have been fabricated in unpassivated, SiO 2 passivated, and Al 2O 3 passivated configurations. The fabrication procedure is described and data pertaining to forward and reverse characteristics, yield and storage characteristics are presented. The Schottky barrier height is characterized by four independent measurements with excellent agreement between the various measurements. The barrier height is in the 0·710–0·760 V range and the typical ideality factor is ≤1·05. The devices exhibit ideal Schottky barrier behavior at least over the −50−100°C temperature range. The current gain of Schottky barriers with different Al layer thicknesses is measured under static electron bombardment over the 1–30 keV energy range. From these measurements, the average energy required to create a hole-electron pair is determined to be 3·44±0·2 eV. Using the gain-energy characteristic, it is possible to identify an optimum accelerating potential for each target. This optimum accelerating potential is in good agreement with that obtained theoretically from consideration of target losses. No junction instability is observed due to electron irradiation for beam current densities up to 0·314 A/cm 2 and target current densities exceeding 1000 A/cm 2. Further, no significant device degradation is observed for target dissipated power densities exceeding 50 kW/cm 2. Under pulse mode dynamic testing, output pulses of 13·1 A with a measured risetime of 0·72 nsec into the 10 Ω optimum load are obtained. When the output risetime is corrected for beam resetime (∼0·60 nsec), an output/risetime of 13·1 A/0·40 nsec is obtained. This is within a factor of 2 of the theoretical output capability of an optimized target; the difference is due to the capacitance of the guard-ring. The amplifier pulse mode efficiency is 85 per cent. The low pass bandwidth is 875 MHz, and the Pf 2 figure is 82 W-GHz 2. In addition, small-signal transconductance and power gains of 4·35 ℧ and 40 dB, respectively, are achieved. No output pulse distortion or pulse height deterioration is noted for pulse widths up to 130 nsec having 13·0 A amplitude under prolonged bombardment of our devices. This indicates that if any insulator charging is occurring, it does not result in any deleterious effects on the target performance.