Noise properties and time response of the staircase avalanche photodiode

The staircase avalanche photodiode is a novel graded-gap superlattice device that is expected to detect photons quite noiselessly. It is designed in such a way that only electrons impact-ionize, thereby eliminating the feedback noise associated with conventional two-carrier avalanche devices. Because the electron multiplication can occur only at a small number of discrete locations in the device, the variability of the number of electrons generated per detected photon is minimized. The excess noise and the electron counting distribution are obtained as a function of the number of stages in the device and the impact-ionization probability per stage, for instantaneous multiplication. The (single-photon) impulse response function is calculated when the effects of (random) transit time are incorporated into the carrier multiplication process. Inclusion of the time dynamics is essential for determining the time course of the current generated by the device in response to pulses of light. This, in turn, permits bit error rates to be calculated for systems incorporating the device. For a five-stage quaternary device the gain-bandwidth product is calculated to be in the vicinity of 600 GHz.