Optical receivers based on superlattice avalanche photodiodes: effect of number of stages

Recently, there has been considerable interest in superlattice avalanche photodiodes (SAPDs) as photodetectors for optical receivers. This paper describes the influence, on receiver sensitivity, of the number of multiplication stages of these devices, taking into account both residual hole ionisation and dark current. It is shown that SAPDs with a large number of stages only offer a sensitivity improvement when the hole to electron ionisation rate ratio k is kept to a very low value. As k increases, a small number of stages are required for better sensitivity, and this also facilitates high speed operation.