Fabrication of biomimic GaAs subwavelength grating structures for broadband and angular-independent antireflection

We combine interferometric lithography and inductively coupled plasma etching to fabricate GaAs subwavelength grating (SWG) which mimics the moth eye structures. Through the modification of morphology parameters, including profile, height and packing fraction, tapered, high-aspect-ratio and closely-packed GaAs SWGs are obtained. The measurement of spectral reflectance of the fabricated SWGs shows that reflection has been dramatically reduced compared to the polished GaAs surface. Particularly, the optimized SWG structures exhibit an average reflection below 5% in the wavelengths ranging from 350 to 900 nm. Furthermore, the angular-independent property is demonstrated by measuring the reflectance versus varying angles of incidence at 532 and 632.8 nm wavelengths.

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► Undercut patterns are achieved in interference lithography without interlayer.
► Porous patterns with higher packing fraction than dots are used as etching masks.
► Photoresist-reflow technique is used to further increase the packing fraction.
► ICP etching recipes are optimized to control the depths, sidewalls and profiles.
► The fabricated structures exhibit an extremely low spectrum reflectance (<5%).