Three-color $(λp1∼3.8 μm,$ $λp2∼8.5 μm,$ and $λp3∼23.2 μm)$ InAs/InGaAs quantum-dots-in-a-well detector

We report a three-color InAs/InGaAs quantum-dots-in-a-well detector with center wavelengths at $∼3.8,$ $∼8.5,$ and $∼23.2 μm.$ We believe that the shorter wavelength responses (3.8 and $8.5 μm)$ are due to bound-to-continuum and bound-to-bound transitions between the states in the dot and states in the well, whereas the longer wavelength response $(23.2 μm)$ is due to intersubband transition between dot levels. A bias-dependent activation energy ∼100 meV was extracted from the Arrhenius plots of the dark currents, which is a factor of 3 larger than that observed in quantum-well infrared photodetectors operating at comparable wavelengths.