Design and simulation of two-color mid-infrared photoconductors based on intersubband transitions in quantum structures

In this work, a novel design of a two-color mid-infrared photoconductor at room temperature exploiting the superposition of different sizes of PbS/ZnS core/shell quantum dots as an absorber is introduced. The designed structure is simulated in the way that it can be fabricated by solution process method. This new approach is adjusted to detect two distinct tunable mid-infrared wavelengths with peaks at the 4 mu m and 5 mu m simultaneously by absorbing the incident photons through intersubband transitions. Two independent energy contacts based on PbS/AlAs core/shell quantum dot structure are deposited on interdigitated contacts for extracting the excited carriers from the active region through the tunneling process. Since the output photocurrent is generated by this resonance tunneling process, the dark current has been notably reduced, therefore the proposed device can operate at high detectivities. To model the proposed two-color photoconductor the developed coupled rate equations and Schrodinger-Poisson equations have been soleved self consistently. Based on simulation results by considering non-idealities in the modelling of the proposed device, for the absorption of 5 mu m (channel-1) and 4 mu m (channel-2), the peak responsivity R is about 9 (A/W), and the high specific detectivity D* is obtained 5 x 1011 (cm Hz1/2/W) for both channels. Therefore, this high-detectivity two-color QDIP can be utilized in multiple applications such as wideband spectrum analyzer, night vision technology, multi-wavelength infrared camera, spectroscopy, and battlefield-imaging.