High temperature operation of quantum dots-in-a-well infrared photodetectors

Systematic study of various types of intersubband transitions in the quantum dots-in-a-well (DWELL) infrared photodetectors has been presented. By changing the thickness of the quantum well, the excited state energy can be tuned with respect to the barrier, without altering the quantum dot ground state. Bound to continuum transitions offer very high extraction probability for photoexcited electrons but poor absorption coefficient, while the bound to bound transitions have higher absorption but poorer extraction probability. Bound to quasi-bound transition is optimum for intermediate values of electric fields with superior signal to noise ratio. The bound to quasi-bound device has the detectivity of 4 × 1011 cm Hz1/2 W−1 (+3 V, f/2 optics) at 77 K and 7.4 × 108 cm Hz1/2 W−1 at 200 K, which is highest reported detectivity at 200 K for detector with long wave cutoff wavelength. High performance focal plane arrays have been fabricated with noise equivalent temperature difference of 44 mK at 80 K for 6.1 μm peak wavelength.