Impedance and g-r noise of n-type gold-doped silicon under space-charge conditions

Abstract

Impedance and current-noise measurements were made on n-type gold-doped silicon single crystals provided with electron-injecting contacts. The d.c. current is proportional to the applied voltage in the ohmic regime considered here. The capacitance is both frequency and d.c. bias dependent at frequencies below the reciprocal electron transit time. In addition, the capacitance shows a sinusoidal behaviour as a function of frequency under certain conditions. The a.c. resistance, equal to the d.c. resistance at lower frequencies, rapidly decreases at frequencies around the reciprocal free-electron lifetime and becomes constant at higher frequencies; moreover, the magnitude depends on the d.c. bias. The observed generation-recombination (g-r) noise is trapping noise associated with a gold-acceptor level at 0.54 eV below the conduction band. The frequency behaviour of the g-r noise spectra depends on d.c. bias voltage at the higher levels where the free-electron transit time becomes smaller than both the free-electron lifetime and the dielectric relaxation time. The free-electron lifetime is found to be about 1 μs at room temperature.