We present a method for characterizing avalanche photodiode (APD) photon-counting detector efficiency as a function of active area. Various shallow-junction silicon APDs having a novel active area were manufactured and tested. We show that cylindrical and checkquerboard-shaped active areas have dark counts two orders of magnitude lower than standard circular devices with an equivalent active area. A parallel implementation of small active areas creates gettering sites for defects to migrate to, which is believed to create relatively defect-free active areas as the perimeter-to-area ratio is increased. However, a compromise between a large perimeter-to-area ratio and a structure useful for practical applications must be considered to optimize the detector.