EXCESS NOISE STUDIES ON AVALANCHE PHOTODIODES
Scansen, Donald Wayne
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An experimental apparatus for carrying out electrical noise measurements on various semiconductor devices over a broad temperature range was constructed. Commercially available avalanche photodiodes (APDs) could be illuminated over the wavelengths 420 nm to 2 gm and the noise current spectrum from 10 Hz to 10 kHz could be measured by a phase sensitive detection system. The noise above normal shot noise in germanium, silicon, and indium-gallium-arsenide avalanche photodiodes was studied as a function of temperature and wavelength over their photosensitive range. Noise spectra in the frequency range 0.01-10 kHz exhibited considerable 1/f type noise at the lowest frequencies. The 1/f noise was especially strong for the indium-gallium-arsenide APD with the 1/f behavior extending up to -2 kHz. The excess noise in the flat-band region was investigated for all three APDs to determine the excess noise factor, F, as a function of temperature and wavelength. The ratio of the electron-to-hole ionization coefficients, k, was determined from the excess noise factor. It was found that for all three APDs, F and hence k were independent of the illumination wavelength and the temperature over the range examined. The experimental ionization coefficients were compared with the calculated values in the literature and discussed within the theoretical framework of Webb, McIntyre, and Conradi. In addition, the temperature dependence of the multiplication factor under a constant reverse bias voltage was also examined.