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

The performance of the InP-InGaAs avalanche photodiode (APD) at low bias voltages has been investigated directly from its impulse response without using any fitting parameters. The important mechanisms responsible 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 the depleted region of the absorption layer. A time-recurrence relation for the emission of holes from the trap has been derived and special attention has been paid to the velocity of carriers at low fields. The delay in the process of diffusion of photogenerated holes has been taken into account in obtaining the impulse response. The bandwidth at different gains have been calculated 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 of an earlier published work on InP-InGaAs APD.