Noise Equivalent Circuit Model of Thin Avalanche Photodiodes

In this letter, a circuit model of noise is presented for thin avalanche photodiodes. By defining an effective electric field over the multiplication region and using position-dependent ionization coefficients, the model tries to include the effects of carrier's dead space and previous ionization history. Then, using a predicted multiplication gain, the model obtains the photocurrent response and output noise spectrum. The excess noise factor and spectral signal-to-noise ratio obtained from the proposed model are compared with available experimental data for different widths of multiplication region. The model is suitable for sensitivity and gain-bandwidth analysis.