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InAs/InGaAs quantum dots infiared photodetectors (QDIPs) were studied. We report an InAs/In0.15Ga0.85As QDIP with bias-dependent multispectral characteristics. The QDIP sample was grown on a semi-insulating GaAs(001) substrate by solid-source molecular beam epitaxy (MBE). This QDIP sample consisted of five stacks of InAs pyramidal QDs capped by InGaAs and sandwiched between heavily-doped GaAs layers. By introducing In into the GaAs cap layers, we could change the intersubband transition in the QDs. Fourier transformation infrared spectroscopy measurement showed a peak photoresponse at the wavelength of ~5.6μm for a bias of -0.5V. At the bias of -0.8V, a photoresponse at the wavelength of ~9.lμm could be observed; the magnitude of photoresponse was comparable to that of the ~5.6μm peak. With further increment of the bias the photoresponse at ~9.lμm dominated the spectrum. The spectrum also indicated that the photoresponse was due to a band-to-band intersubband transition in the InAs QDs.