Low-bias performance of avalanche photodetector - A time-domain approach

In this paper, the performance of the InP-InGaAs avalanche photodiode (APD) at low bias voltages has been investigated directly from its impulse respo nse without using any fitting parameters. The important mechanisms responsi ble for low-bias performance are the emission of holes from the InP-InGaAs interface potential-trap in the valence band, the velocity of the carriers, and the diffusion of photogenerated holes from the undepleted region to th e depleted region of the absorption layer. A time-recurrence relation for t he emission of holes from the trap has been derived and special attention h as been paid to the velocity of carriers at low fields. The delay in the pr ocess of diffusion of photogenerated holes has been taken into account in o btaining the impulse response. The bandwidth at different gains have been c alculated by taking the fast Fourier transform (FFT) of the current impulse response. The gain-bias and gain-bandwidth characteristics show reasonably good agreement between the data from the model and the experimental data o f an earlier published work on InP-InGaAs APD.