We investigate the materials properties and dark currents of planar InP/InGaAs avalanche photodiocles (APDs) in which the p-clopant, Zn, is introduced by diffusion in an MOCVD reactor using climethylzinc (DMZn) as the source. APD dark currents are compared with low-temperature photoluminescence (PL), electrochemical capacitance-voltage (ECV) and secondary ion mass spectroscopy (SIMS) measurements of layers diffused under the same set of conditions. Device dark currents exhibit both surface-related and bulk contributions, with the bulk contribution appearing as a step increase in the current near the punch-through voltage. The bulk dark current contribution depends on the diffusion process parameters and is correlated with the total Zn incorporation and the intensities of the InP and InGaAs PL peaks. A variation of three orders of magnitude is observed in the bulk dark current contribution as diffusion conditions are varied. Crown Copyright (C)) 2013 Published by Elsevier B.V. All rights reserved