Linear-mode single-photon APD detectors

Abstract

In the past, it has been necessary to operate avalanche photodiodes (APDs) in Geiger mode to perform photon counting. The gain and noise performance of available linear-mode APDs was too poor to detect the photocurrent pulse from a single photon using existing amplifier technology. We review the performance thresholds required to achieve linear-mode photon counting, and present measurements from two APD designs that meet the gain and noise requirements. The first design is a previously-reported vertical-junction, electron-avalanche HgCdTe device fabricated from 4.06-μm-cutoff liquid phase epitaxy (LPE)-grown material. These HgCdTe APDs have an excess noise factor of approximately F~1 at a gain of M=150 when measured at 196 K. The second design is a novel InAlAs/InGaAs structure grown by molecular beam epitaxy (MBE) entirely from alloys lattice-matched to InP. The maximum gain found for this new design was as high as M=2000 at 235 K, but the principle of its operation limits the best noise performance of the prototype to gains below M=20, for which it has an excess noise factor of F~2.3 at room temperature (corresponding to k~0.02 when fit to McIntyre's model). This design can be scaled to deliver the same noise performance at higher gains.