Analysis of nano-grating-assisted light absorption enhancement in metal–semiconductor–metal photodetectors patterned using focused ion-beam lithography

We present finite-difference time-domain (FDTD) analysis results of light absorption enhancement factor dependence on the profile shape of nano-gratings etched into the surfaces of metal–semiconductor–metal photodetector (MSM-PD) structures. The MSM-PDs patterned by nano-gratings are optimized geometrically, improving the light absorption near the design wavelength through plasmon-assisted electric field concentration effects. FDTD simulation results show about 50 times light absorption enhancement prediction for 850 nm light due to improved optical signal propagation through the nano-gratings in comparison with the conventional MSM-PD designs employing only a subwavelength aperture. We also report on the nano-grating profile shapes obtained typically in our experiments using focused ion-beam lithography and discuss the dependency of light absorption enhancement on the geometric parameters of nano-gratings inscribed into MSM-PDs.

Research Highlights
► Focused ion-beam lithography applied for the fabrication of metal–semiconductor–metal photodetectors (MSM-PDs).
► Light-capture performance of new MSM-PD structure designs employing metal nano-gratings analyzed for different cross-sectional geometries.
► Experimental characterization results of FIB-milled nano-gratings are discussed.
► Significant performance improvements predicted for MSM detectors with nano-gratings due to surface plasmon propagation.
► The effect of non-ideal manufacturing conditions is quantified.