Near Unity Absorption in Nanocrystal Based Short Wave Infrared Photodetectors Using Guided Mode Resonators

Nanocrystals appear as versatile building blocks for the design of low-cost optoelectronic devices. The design of infrared sensors based on nanocrystals is currently facing a key limitation: the short carrier diffusion length resulting from hopping transport makes that only a limited part of the incident light is absorbed. In order to enhance the device absorption, we use guided mode resonance (GMR). The method appears to be quite versatile and is applied to both PbS and HgTe nanocrystals presenting, respectively, cutoff wavelengths at 1.7 and 2.6 mu m. The designed electrodes present a large enhancement of material responsivity by a factor of approximate to 250, reaching an external quantum efficiency of 86% for PbS and 340% for HgTe. This increase of the response can be deconvoluted in a factor of 3 for the enhancement of the absorption and a factor of 80 for the photocurrent gain. This method can also be suited to finely tune the cutoff wavelength of the material thanks to geometrical parameters at the device level. The obtained devices are now only limited by the material noise.