Frequency dependence of the reverse-biased capacitance of gold-doped silicon P+N step junctions

The experimentally observed frequency dependences of the reverse-biased capacitance of gold-doped silicon step junctions over the frequency range from 10 cps to 30 Mc are found to be in agreement with a simple physical model which takes into account the charge condition and the charging and discharging time constant of the deep-gold acceptor level in the transition region of the junction. Analysis based on the simple physical model provides explicit theoretical formulas for the junction capacitance at low- and high-frequency limits which show that the high-frequency capacitance under reverse bias is approximately proportional to
\sqrt{N_{D} - N_{Au}}
and is considerably reduced below the low frequency or dc capacitance if the donors are nearly compensated by the gold. The frequency effect is important for deep energy level impurities and becomes negligible if the impurity level is at or near the band edges. The presence of gold, however, has negligible effect on the avalanche breakdown voltage if
N_{Au} < N_{D}
.