Spectral response and device performance tuning of long-wavelength InAs QDIPs

Long-wavelength InAs QDIPs with different thicknesses of InGaAs cap layer in the confinement-enhanced dots-in-a-well (CE-DWELL) structure were investigated. The sample with 3 nm cap layer shows primarily single band detection at 7 mu m that stems from the transition between QD states, but the 5 nm and 7 nm samples reveal voltage-tunable dual band detection in the region of 6-11 mu m from transitions to the states in the dots as well as the states in the well. The wavefunction coupling of transition states is effectively modified by the change of cap-layer thickness and the bias polarity, which leads to the observed spectral change and demonstrates the flexibility of the CE-DWELL QDIPs. For higher peak quantum efficiency (QE), thin InGaAs cap layers are used to obtain focused absorption strength. With 3 nm cap layer in the CE-DWELL, a respectable QE of 7.23% is reached for 10-stack QDIPs with 7 mu m detection wavelength at 77K. and a high detectivity of 3.4 x 10(10) Jones is also obtained. (C) 2010 Elsevier B.V. All rights reserved.