SBIR Phase I: Geiger Mode Avalanche Photodiodes for Photon Counting from 0.9 micrometers to 2.0 micrometers

This Small Business Innovation Research (SBIR) Phase I project will develop and deliver an avalanche photodiode sensitive from 0.9 to 2.0 microns, enabling solid-state photon counting applications in this wavelength band. The avalanche photodiode will operate in Geiger mode, wherein the device is cooled to minimize the dark current rate, and biased slightly above breakdown. During Phase I, our commercial avalanche photodiodes will be evaluated for use in Geiger mode. These detectors are sensitive from 0.9 to 1.7 microns. The experimental setup for gated photon counting measurements will be established, and optimum-operating temperatures determined. In Phase II, the cutoff wavelength will be extended to achieve a cutoff wavelength of 2.0 microns at the optimum operating temperature. The cutoff wavelength will be extended using one a technique for decreasing the effective band gap of InGaAs. The first method uses graded layers of InAsP of varying composition to develop a lattice-matched substrate to high In content InGaAs. The second method uses strain-compensation expitaxial growth techniques to grow high In content InGaAs without incorporating misfit dislocations, which act as dark current generation sites. The Phase II deliverable will be a Dewar based photon-counting system for 2.0-micron wavelengths. Applications of this technology would immensely benefit spectral analysis in the range from a 1.0 micron to 2.0 micron solid-state photon counting detector. Geiger mode long wavelength APDs can be used in embedded spectrometers for remote sensing, gas detection, or in applications where weak fluorescence signals must be detected.