The rigorous coupled-wave analysis (RCWA) was used for the full-field electromagnetic calculation. The number of the Fourier harmonics was set to 101, which was confirmed to be large enough to reach convergence. The refractive index of the Al2O3 layer was obtained by using ellipsometry (fig. S8). The refractive index of Al was chosen from the literature (38). The dielectric constant of the InAs layers was described by the Drude model. The effective electron mass for the high-doped InAs was 0.17 me, leading to a plasma frequency of 1.37 × 1015 rad/s. The effective electron mass at the band edge was 0.027 me (39), and that of the low-doped (n+) InAs layer was obtained as 0.039 me by using a linear interpolation between the high-doped InAs and the band edge, which leads to a plasma frequency of 9.0 × 1014 rad/s. The collision frequency was determined by finding the best agreement with the experimental measurement. Physically reasonable values consistent with previous literature (34) of 2.0 × 1013 rad/s for the low-doped InAs and 5.0 × 1013 rad/s for the high-doped InAs were obtained, respectively. The infinite-frequency permittivity for both InAs layers was 12, which was obtained from the literature (40). The depletion layer at a bias of 0 V, 24.5 nm in the top (near Al2O3) n+ InAs layer and 24 nm in the bottom (near n++ InAs) layer, was formed. Under a negative bias of −15 V, the depletion layer thickness was 1.5 nm. A positive bias with +15 V induced the formation of an accumulation layer with a thickness of 0.5 nm and an increase in the plasma frequency of 9.2 × 1014 rad/s while maintaining the collision frequency. The plasma frequency at the positive bias and the depletion and accumulation layer thicknesses were adjusted to reproduce the experimental results for various grating geometries. The comparison between the reflection measurement (FT-IR) and simulation (RCWA) for various grating widths and periods confirmed the agreement (figs. S9 and S10).

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