Revealing Structural Disorder in Hydrogenated Amorphous Silicon for a Low-Loss Photonic Platform at Visible Frequencies

The high refractive index of hydrogenated amorphous silicon (a-Si:H) at optical frequencies is an essential property for the efficient modulation of the phase and amplitude of light. However, substantial optical loss represented by its high extinction coefficient prevents it from being utilized widely. Here, the bonding configurations of a-Si:H are investigated, in order to manipulate the extinction coefficient and produce a material that is competitive with conventional transparent materials, such as titanium dioxide and gallium nitride. This is achieved by controlling the hydrogenation and silicon disorder by adjusting the chemical deposition conditions. The extinction coefficient of the low-loss a-Si:H reaches a minimum of 0.082 at the wavelength of 450 nm, which is lower than that of crystalline silicon (0.13). Beam-steering metasurfaces are demonstrated to validate the low-loss optical properties, reaching measured efficiencies of 42%, 62%, and 75% at the wavelengths of 450, 532, and 635 nm, respectively. Considering its compatibility with mature complementary metal-oxide-semiconductor processes, the low-loss a-Si:H will provide a platform for efficient photonic operating in the full visible regime.

Automated summary

The high refractive index of hydrogenated amorphous silicon (a-Si:H) at optical frequencies is important for modulating light, but its high extinction coefficient has limited its widespread use. By adjusting chemical deposition conditions to control hydrogenation and silicon disorder, a low-loss a-Si:H material has been developed with an extinction coefficient as low as 0.082 at 450 nm. This material shows promise for efficient photonic operation in the visible spectrum and has been validated through beam-steering metasurfaces with measured efficiencies up to 75%.