Abstract
A simple matrix-method model is presented for calculating the impedance and the
short-circuit frequency response of an avalanche photodiode (APD) with arbitrary layer
structures and absorption/multiplication coefficients. In our matrix method model, the
depletion region of the APD is divided into many thin layers. In each thin layer the
absorption and the multiplication coefficients are assumed to be uniform. As an example,
we use this matrix-method model to analyze in detail a resonant Ge/Si SACM (separated
absorption charge multiplication) APD. The impedance analysis shows that the avalanche
region is equivalent to an LCR-circuit including a negative resistance, an inductance
with a series resistance, and a capacitance in parallel connection. At higher bias
voltages, the negative resistance and series resistance become very small and
consequently the LCR circuit shows a strong resonance. Furthermore, the inductance also
becomes smaller at higher bias voltages, which introduces a higher resonance frequency.
This increases the 3 dB-bandwidth, in agreement with experiment.
© 2010 IEEE
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