| Popis: |
Systematic characterization 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 quasibound transition is optimum for intermediate values of electric fields with superior signal to noise ratio. The bound to quasibound device has the detectivity of 4×10 11 cm.Hz 1/2 W -1 (+3V, f /2 optics) at 77 K and 7.4×10 8 cm.Hz 1/2 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 6.1μm peak wavelength. |
