Short-wavelength infrared (SWIR, 1 – 3 µm) has emerged as an optimal wavelength for telecommunication, passive night vision, and biomedical imaging. However, the expensive cost of commercial SWIR photodetectors, based on III-V semiconductors, have hindered the spread of SWIR technology. Lead chalcogenide colloidal quantum dots (QDs) hold a great potential as a new material for SWIR detection. They not only have tunable bandgap in SWIR region but also have process compatibility with conventional Si ROIC fabrication process, which remarkably reduces fabrication costs. The performance of photodetectors incorporating PbS QDs, however, is suboptimal and needs further improvement. One of the main factors limiting the performance of QD-based photodetectors is a high density of surface defects. QDs inherently have large surface-to-volume ratios and dangling bonds on the surface acted as trap sites. Various methods to reduce surface defects, such as ligand treatment, have been introduced; however, even after these treatments, QD-based photodetectors still show the relatively low detectivity (D*).<br/>In this work, we use a thermal annealing method to reduce the trap density, thereby improve the performance of photodetectors. Our annealing protocol does not broaden the 1<sup>st</sup>-excitonic absorption peak, confirming that the QDs are not sintered or necked during the thermal cycle.  Our device shows better bandwidth and higher responsivity compared to reference devices without annealing, although the carrier mobility in QD layer is not improved significantly due to lack of sintering. A controlled annealing process doubles the D* at 1300-nm wavelength. Further analysis on the annealed QD layers will be presented.

Improving PbS QD SWIR photodetectors using thermal annealing

2019 Fall National Meeting

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