Polarized front-illumination response in intraband quantum dot infrared photodetectors at 77 K

Multicolor quantum dot infrared photodetectors with normal incidence background limited performance (BLIP) at 77 K were implemented. The devices are composed of self-assembled InAs dots grown on InAlAs barrier layers, lattice matched to InP substrate. These dots are formed in a shape of flattened parallelepipeds. The photoconductive spectra were observed at all polarizations. Normal incidence photocurrent spectra reveal several polarized peaks in the range of 100-400 meV due to intersubband transitions. The detector responsivity at normal incidence is similar to that obtained for polarization normal to the layers, and is comparable to that achieved in quantum well infrared photodetectors (QWIP's). The transition energies, the polarization selection rules, and relative intensities of the peaks were tentatively interpreted in terms of a three-dimensional separation of variables.