Noise in inversion layers near the metal-insulator transition

Power spectra of current-dependent voltage noise in inversion layers near the metal-insulator transition are found to be of the form 1/f beta with beta generally between 1.0 and 1.1. The spectral density is proportional to channel resistance in quantitative agreement with the Hooge relation (1969), but, for constant channel resistance, noise is found to increase with reduction of temperature from 4.2 to 1.5K. The noise is shown to be generated throughout the channel with a correlation length small compared with sample dimensions. The authors cannot explain our results in terms of diffusion or conventional trapping of carriers, and the thermal fluctuation model is shown not to apply to this system. Very low levels of optical illumination modify device characteristics, increase noise and steepen spectra, which results are tentatively attributed to generation of a very low concentration of low-mobility carriers in the oxide.