We describe the calculation of gain and bandwidth of an n + -i-p + avalanche photodiode (APD) for a multiplication layer down to tens of nanometers. The computed results are used to make a comparative study of gallium arsenide (GaAs) and silicon (Si) APDs. In the analysis, the depletion region is discretized into equal energy segments to take into account the discontinuous nature of impact ionization in the multiplication layer due to dead-space effect. Also, the carrier diffusion from undepleted regions is considered to study the effect of low bias on the frequency response. Carrier distribution within the structure is obtained by a numerical solution of coupled equations and recurrence relations. The model is verified with some experimental data taken from literature. Results show that gain increases with bias more rapidly for thinner multiplication layer. The Si APD is thinner than GaAs APD for the same gain at a given bias. Diffusion causes significant reduction of bandwidth at a low gain, with the change being sharper for GaAs APD than for Si APD.
Proc. SPIE. 8549, 16th International Workshop on Physics of Semiconductor Devices
KEYWORDS: Avalanche photodetectors, Ionization, Gallium arsenide, Data modeling, Avalanche photodiodes, FDA class I medical device development, FDA class II medical device development, Physics, Electronics, Performance modeling
The electron initiated avalanche gain and bandwidth are calculated for thin submicron GaAs n+-i-p+ avalanche
photodiode. A model is used to estimate the avalanche build-up of carriers in the active multiplication layer considering
the dead-space effect. In the model, the carriers are identified both by their energy and position in the multiplication
region. The excess energy of the carriers above threshold is assumed to be equally distributed among the carriers
generated after impact ionization. The gain versus bias and bandwidth versus gain characteristics of the device are also
demonstrated for different active layer thicknesses of the APD.