Uncooled, Long-Life Wavefront/Tracking Sensor

The feasibility of using AlGaInAs avalanche photodiodes (APDs) operated in linear mode as high-frame- rate solid state wavefront and tracking sensor elements capable of detecting single photons will be established. The small contrast between electron and hole ionization coefficients in common III-V compound semiconductors like AlGaInAs would normally prohibit their use in photon-counting APDs owing to excess multiplication noise, but an imaginative new application of the impact-ionization engineering (I2E) concept will be used to overcome the limitations of the material. Lower noise will be realized with novel field control and bandgap engineering methods, which achieve greater spatial localization of the impact ionization events resulting in selective electron-initiated ionization and greater correlation between ionization events. Initial simulations predict better than 50% detection efficiency at 1064 nm & 1550 nm, better than 500 MHz bandwidth, and room-temperature single-photon sensitivity when operated in conjunction with Voxtel's low-noise readout integrated circuit (ROIC). The technique is solid state, has demonstrated reliability, has low dark current at room temperatures, and is supported by the tremendous III-V materials infrastructure developed for telecommunications. It therefore offers significant advantages over hybrid, electron-bombarded image tube sensor approaches.