In this study, bias mediated tuning of the detection wavelength within the infrared wavelength region is demonstrated for quantum dots-in-a-well (DWELL) infrared photodetectors. In DWELL structures, intersubband transitions in the conduction band occur from a discrete state in the quantum dot to a subband in the quantum well. Compared to "conventional" quantum dot infrared photodetectors, where the transitions take place between different discrete bands in the quantum dots, new possibilities to tune the detection wavelength window are opened up, partly by varying the quantum dot energy levels and partly by adjusting the width and composition of the quantum well. In the DWELL structure used, an asymmetric positioning of the InAs quantum dot layer in a 8 nm wide In0.15Ga0.85As/GaAs QW has been applied which enables tuning of the peak detection wavelength within the long wavelength infrared (LWIR; 8 - 14 µm) region. When the applied bias was reversed, a wavelength shift from 8.5 to 9.5 µm was observed for the peak position in the spectral response. For another DWELL structure, with a well width of 2 nm, the tuning range of the detector could be shifted from the medium wavelength infrared (MWIR; 3-5 µm) region to the LWIR region. With small changes in the applied bias, the peak detection wavelength could be shifted from 5.1 to 8 µm. These tuning properties of DWELL structures could be essential for applications such as modulators and two-colour infrared detection.