Geiger-mode avalanche photodiodes (GM-APDs) grown by organometallic vapor phase epitaxy are of interest for several low-light-level applications, including laser radars and single-photon-counting optical communications. Materials systems based on GaInAsP lattice matched to InP are critical to the performance of GM-APDs at both 1.06- and 1.55-mu m wavelengths. Growth temperature, growth rate, and V/III ratio were investigated to determine the effect each had on important device parameters, dark count rate and after-pulsing. Improvements of growth conditions led to a 44% reduction in dark count rate (DCR), but after-pulsing behavior, and thus dead time of GM-APDs was unaffected. The improvement of growth conditions has led to devices with DCRs at 300 K of 8 x 10(9) Hz/cm(2) with dead times still at approximately 1 mu s. (C) 2007 Elsevier B.V. All rights reserved.