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The multicolor absorption of MOS SiGe/Si quantum-dot (QD) infrared photodetectors is demonstrated using the boron delta-doping in Si spacers. The energy-dispersive X-ray spectroscopy shows that the Ge concentration in the wetting layers is much smaller than that in QDs. Most holes stay at the ground state in QDs instead of wetting layers. The energy band structure in QDs is calculated to understand the absorption spectrum. The absorption at 3.7-6 mum is due to the intersubband transition in the SiGe QDs. The other absorption at 6-16 mu m mainly comes from the intraband transition in the boron delta-doping wells. Since the broadband spectrum covers most of the atmospheric transmission windows for infrared, the broadband detection is feasible using this device.