comparative study of the optical characteristics in InAs/GaAs quantum-dot infrared photodetectors doped in different positions

We have investigated the optical characteristics of the photoluminescence (PL) and the photoresponse (PR) observed in a series of self-assembled InAs/GaAs quantum dot infrared photodetectors (QDIPs) with different doping positions. The interband PL intensity associated with QDs at near-infrared (1015 +/- 5 nm at 10 K) is strongest for the structure doped in InAs QDs, but the intersubband PR near far-infrared (similar to 5 mum at 18 K) is most sensitive for the device doped in the upper GaAs barrier. Even though the doping in the lower barrier or QDs is effective for the near-infrared photoemission, the far-infrared photoabsorption can be much enhanced by strong carrier confinement for QDIPs doped in the upper barrier under a bias. We suggest that QDIP devices showing stronger PL intensity do not necessarily give larger values of the photoresponsivity.