Characterisation and Simulation of Linear and Geiger Mode Avalanche Photodiodes

Al0.85Ga0.15As0.56Sb0.44 is a wide bandgap material latticed matched to InP. Narrow devices from the literature
show a very low excess noise factor, suggesting a wide disparity between the impact ionisation coefficients.
In this work, a 600 nm pin is experimentally characterised for electron-initiated avalanche multiplication and
excess noise factor. Using these results and those from the literature, a Simple Monte Carlo parameter set was
validated, and the impact ionisation coefficients were extracted for an electric field range of
400 – 1200 kV.cm-1.
A Random Path Length model is a simplistic Monte Carlo model with a short simulation runtime compared to
the more complex Simple Monte Carlo Model. The RPL has previously been used to model breakdown
probability but could not accurately model the time to breakdown due to the limitations imposed by the
saturation velocity assumption. In this work, an enhanced velocity for Si, InP and Al0.85Ga0.15As0.56Sb0.44 was
proposed. The enhanced velocity of these materials was validated against the Simple Monte Carlo model with
good agreement over a wide range of simulated devices.
Finally, a Simple Monte Carlo model parameter set was validated for In0.53Ga0.47As, and the impact ionisation
coefficients were extracted over an electric field range of 80 – 340 kV.cm-1. In0.53Ga0.47As is a common
absorption material for III-V based SAM APDs. In0.53Ga0.47As has previously been characterised to have an
abnormally low electric field election initiated avalanche multiplication due to the large energy offset between
EΓ and the indirect energy valleys. Careful attention was made to ensure the avalanche multiplication
simulations followed both the low and high electric field trends.