The variably spaced superlattice energy filter quantum well avalanche photodiode: A solid-state photomultiplier

A new highly-efficient, single-carrier-type avalanche photodiode is presented based on impact ionization across the band edge discontinuity. A resonant tunneling superlattice structure, the variably spaced superlattice energy filter (VSSEF), is used to selectively tune the incident electron distribution to the quantum well impact excitation energy. The gain is greatly enhanced within the structure for two reasons: most of the incident electrons contribute to the ionization process in each stage of the device, and the lowest lying subbands, which are by far the most highly occupied, can be ionized. It is predicted that multiple ionization, similar to secondary emission in photomultiplier tubes, can occur thereby greatly enhancing the gain of the device. The device behaves in principle more like a photomultiplier than other existing solid-state photodetectors since more than one secondary carrier can be produced per initiating carrier per stage of the device. Representative devices are presented for the Ga0.47In0.53As/ (Al0.48In0.52AsBa0.17Sr0.83F2) and GaAs/(AlGaAs-ZnSe) material systems based on a calculation using first an uncoupled quantum well system and second, a complete resonant tunneling coupled quantum well calculation based on an Airy function approach.