Enhanced normal incidence photocurrent in quantum dot infrared photodetectors

The authors report an enhancement in the photocurrent caused by normal incidence (s-polarization) radiation in a quantum dot-in-a-well (DWELL) based infrared photodetector. The s-to-p polarization ratio was increased to 50%, compared to the 20% in conventional quantum dot (QD) detectors. This improvement was achieved through engineering the dot geometry and the quantum confinement via postgrowth capping materials of the QDs. The effect of the capping procedures was determined by examining the dot geometry using transmission electron microscopy (TEM) and s-to-p ratio of the polarized photocurrent in the DWELL infrared photodetector. The TEM image shows a quantum dot with a reduced base of 12 nm and an increased height of 8 nm. The infrared photodetector fabricated from this material shows peak photodetectivities of 1 x 10(9) cm Hz(1/2)/W at 77 K for a peak wavelength of 4.8 mu m and 1 x 10(7) cm Hz(1/2)/W at 300 K for a peak wavelength of 3.2 mu m. The dark current density is as low as 2 x 10(-4) A/cm(2) and the photoconductive gain is 100 at the optimal operating bias. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3562186]