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.