Plasmonic Nanostructures for IR Photodetectors

Plasmonic nanostructures have been used in the last years to improve the photocurrent generation in detectors and solar cells by plasmonic light trapping or electromagnetic field local enhancement due to the excitation of... [ view full abstract ]

Plasmonic nanostructures have been used in the last years to improve the photocurrent generation in detectors and solar cells by plasmonic light trapping or electromagnetic field local enhancement due to the excitation of localized surface plasmons (SPPs). These plasmonic devices combine a metallic nanostructures that supports SPPs with photonic detection using electron-hole pair photogeneration or   internal photoemission effect (IPE).

The paper presents simple and low cost processes for fabrication of IR plasmonic photodetectors.  We used Ag nanoparticles (NPs) to improve the light absorption in PbS quantum dots (QDs) photoconductors and in silicon Schottky  IPE based  photodetectors. The NPs have been obtained using either chemical reaction of AgNO₃ and oleylamine solution at 180°C, or vacuum deposition of very thin layers followed by thermal annealing.

Ag NPs obtained by chemical synthesized were mixed with PbS QDs (1.5 nm diameter) in different concentrations and deposited on pre-patterned electrodes (oxidized Si substrate) using the layer-by-layer approach to obtain PbS QDs-Ag NPs based photodetectors. The second approach was used to obtain Ag islandized layers on Si Schottky or MSM photodetectors to improve the efficiency of IPE. The Ag NPs were characterized using SEM, AFM. The size can be tuned by modifying the process parameters. Fig. 1 shows examples SEM images of the obtained Ag NPs in different conditions. Absorption spectra in IR were characterised with FT-IR spectrometer VERTEX 80/80v. The I-V characteristics in dark and under illumination were measured using a Semiconductor Characterization System Keithley 4200-SCS with shielded probe station and monochromatic light sources (laser diodes and LEDs).

The paper presents the influence of NPs size, concentration, device lay-out on the photoresponse and the spectral characteristics. In fig. 2 and 3 two examples of measurement results are presented. The measurements indicate that Ag NPs can improve the responsivity in IR of  the PbS QD-based photodetectors,  and  of the Si Schottky diodes based on IPE as well.  Higher responsivities compared with those recently reported in literature for IPE photodetectors were obtained: up to 11mA/W at 1550 nm.  

Acknowledgements: The work was supported by the Romanian National Research Programe PN III, project PN-III-P2-2.1-PED-2016-0307 TemptSys.