Excess Noise in Semiconductors

Abstract:
Critical point polarization fluctuations in ferroelectric triglycene sulfate crystals were measured at the curie temperature by observing noise voltages between electrodes applied to the crystal. In barium titanate crystals a thermal Barkhausen noise with a 1/f power spectrum is observed when the crystal temperature is passed slowly through the curie point. Experimentally it was found that the noise voltage appearing across a metallic conductor heated to high temperatures by dc current flow is given by the Nyquist theorem, even though the conductor is not in thermodynamic equilibrium. In semiconductors fluctuations in optical absorption at wavelengths beyond the fundamental absorption edge caused by free carrier scattering are expected. A simple experiment employing an infrared interferometer was capable of detecting such fluctuations in optical absorption