Near single carrier-type multiplication in a multiple graded- well structure for a solid-state photomultiplier.

We report the observation of very large ionization rate ratios (beta/alpha) in multiple graded-well Al(0.48) In(0.52)As/Ga (0.47)In(0.53)As avalanche photodiodes, grown by MBE. Avalanche multiplication occurs when holes heated by the field in the barrier layers impact ionize thermally-generated holes dynamically stored in the wells over the valence band-edge discontinuity. Since electrons are not confined in the graded structure, there is no multiplication of electrons by this process. This is the first observation of near single carrier-type multiplication in a III-V material.