In this article, quantum-dot infrared photodetectors (QDIPs) with 10-and 30-period InAs/GaAs quantum-dot structures are investigated. High responsivity of 2.37 A/W and detectivity of 2.48 X 10(10) cm Hz(1/2)/W for 30-period QDIPs under 10 K are observed at -2.7 and 1.2 V, respectively. Almost symmetric photocurrents and dark currents under positive and negative biases are observed for both devices, which indicate a minor influence of the wetting layer on the performance of QDIPs. Lower dark current and increased photocurrent for the 30-period QDIPs would predict a better performance for devices with over a 30-period QD structure. (c) 2005 American Vacuum Society.