Nanostructured InGaAs Photodetectors for Infrared Imaging

Despite the outstanding performances reached by today’s infrared quantum photo-detectors, progresses have been stagnating for years. Their detectivity is mainly limited by the noise generated by the dark current requiring... [ view full abstract ]

Despite the outstanding performances reached by today’s infrared quantum photo-detectors, progresses have been stagnating for years. Their detectivity is mainly limited by the noise generated by the dark current requiring cooling down the devices at cryogenic temperatures. To go beyond this last limit we combine a P-i-N semiconductor structure with a nano-antenna based on a guide mode resonance (GMR) effect. The optical and electronic properties of devices are significantly modified by reducing by more than one order of magnitude the active area dimensions, paving the way for a new generation of photo-detector [1].
The device is a resonant photodiode transferred onto a gold mirror. It comprises a sub-wavelength dielectric grating inserted between the gold mirror and the detector (see Figure attached). The structural parameters were optimized to maximize a main resonance around λ= 1,55 µm for both polarizations. The thickness of the InGaAs absorbing layer was reduced to 90 nm in order to improve the signal-to-noise ratio. As InP and InGaAs have similar refractive indices, the whole semiconductor heterostructure acts as a waveguide. The modal analysis shows that under normal incidence, propagation inside the semiconductor cavity involves some modes coming from the combinations of diffracted orders and the non-diffracted wave [2]. At resonances the electric field intensity maps show that the path of the photo-carriers is reduced to about 100 nm, and is localized in a high static electric field area that maximizes their collection efficiency.
Clean room processes were developed in order to fabricate individual GMR pixels of various sizes. They were opto-electrically characterized over the 1,2-1,8 µm range for an unpolarized focused beam. The spectral EQE measurement showed a main resonant response around λ= 1,55 µm with a maximum value of 71% and an averaged value of 50% over a 450 nm bandwidth. The good agreement between experimental and calculated EQE indicates a near perfect collection of the photo-carriers. Compared to the state-of-the-art InGaAs resonator detector, we showed a broader spectral response compatible with SWIR imaging.
[1] M. Verdun et al., JAP 120(8), 2016.
[2] M. Verdun et al. APL 108(5), 2016.