Optimization, Fabrication, and Characterization of Dual-Band InGaAs nBn Photodetectors

Şahin, Alper
Shortwave and extended shortwave infrared regions are attracting significant attention since many applications utilize infrared wavelengths between 1-3 μm. Gas sensing, spectroscopy, food safety, astronomy, imaging, and optical communication are among the applications that utilize SWIR/eSWIR detectors. Typically Low radiation levels at SWIR/eSWIR bands require SWIR/eSWIR photodetectors to have outstanding performance, including high quantum efficiency and very low dark current. Photodetectors built with InGaAs lattice matched to InP provide the best performance at affordable costs, although they suffer from surface leakage currents. However, extending the cut-off wavelength from 1.7 μm to 2.5 μm causes material quality to decrease significantly due to the lattice mismatch between InGaAs/InP. nBn detectors, introduced relatively recently, offer effective solutions to dark current mechanisms due to surface leakage and material-related problems. In the scope of this thesis study, an nBn type InGaAs photodetector at 1.7 μm / 2.0 μm with dual-band capacity was designed, fabricated, and characterized. An unintentionally doped InAlGaAs layer was placed between two n-type InGaAs absorbers as the barrier material. p-type delta doping was applied to the barrier to arrange the band structure of the overall device so that there is no valance band offset that hinders the flow of the photoexcited minority carriers. Dark current measurements at 300 K on a large area pixel yield 3.40 mA/cm^2 and 0.61 μA/cm^2 for the eSWIR and SWIR sides, respectively. Dark current values at 200 K for the eSWIR decreased to 8.05 μA/cm^2, while the SWIR side provided 1.09 nA/cm^2. Arrhenius plots for both SWIR and eSWIR sides presented a fixed slope, meaning tunneling and surface components were successfully eliminated. Suppression of surface leakage currents was also verified with dark current measurements on different area pixels. Optical measurements without anti-reflective coating yielded 67% and 53% peak quantum efficiencies for eSWIR and SWIR sides, respectively. High quantum efficiency values acknowledged the absence of valance band offset.


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Citation Formats
A. Şahin, “Optimization, Fabrication, and Characterization of Dual-Band InGaAs nBn Photodetectors,” M.S. - Master of Science, Middle East Technical University, 2022.