Current-gain characteristics of Schottky-barrier and p-n junction electron-beam semiconductor diodes

Measured and calculated current gains are presented for silicon, gallium-arsenide, and gallium-arsenide-phosphide electron-beam-semiconductor Schottky-barrier diodes. Silicon and gallium-arsenide-phosphide (GaAs0.7P0.3) diodes, having comparable critical voltages, provided current gains of 1400 and 960, respectively, at the beam voltage of 9 kV. A gallium-arsenide diode had a gain of 2100 at 12.7 kV. It is shown that Schottky-barrier diodes provide a good diagnostic tool for measurement of energy per electron-hole pair in semiconductors. The average pair energies for silicon, gallium arsenide, and gallium arsenide phosphide, determined by use of these diodes, were 3.6, 4.6, and 5.2 eV, respectively. Expressions for static and time-dependent current gains are derived for abrupt p-n-junction EBS diodes based on measured and simplified (constant) lineal densities of secondary-electron generation. It is shown that the current gain of p-n junctions is generally lower than that of Schottky-barrier diodes and decreases with increasing density of the semiconductor. For shallow (<0.2 µmr) silicon junctions, the calculated current gain is only slightly smalle. (<8 percent) than that of comparable Schottky-barrier diodes Measurements performed on a relatively deep (0.8 µm) silicon p-n junction, which provided a current gain of 2500 at the beam voltage of 13.6 kV, are in good agreement with the theory. The gain of this junction was typically 40 percent lower than that of a comparable Schottky-barrier diode. This difference was significantly greater for gallium arsenide as a result of its higher density. Approximate expressions and calculations are presented for estimating frequency limitations of p-n-junction EBS targets.