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 μm 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 μm 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 μm detection wavelength at 77 K, and a high detectivity of 3.4 × 1010 Jones is also obtained.