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 (β/α) in multiple graded-well Al
0.48
In
0.52
As/Ga
0.47
In
0.53
As avalanche photodiodes (APD's) grown by molecular beam epitaxy (MBE). The multiplication effects can be explained by impact ionization across the valance band-edge discontinuity of thermally generated holes which are dynamically stored in the wells. 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 semiconductor material.