Enhanced ultrabroadband antireflection properties of ZnTe crystal with sub-wavelength surface structures by maskless reactive ion etching method

ZnTe as the electro-optic (EO) crystal has been widely used in the THz spectroscopy and imaging system, however, the maximum generation and detection efficiency have yet to be achieved due to surface reflection. In this work, antireflective sub-wavelength structures (SWSs) on ZnTe crystals were fabricated by reactive ion etching (RIE) method. The surface morphology was investigated by tailoring etching time and radio-frequency power. The SWSs with dimensions less than 20 nm spontaneously formed without artificial mask, bringing roughness of 2.07 nm. The infrared and visible-near-infrared transmission spectra demonstrated that the mean transmittance of ZnTe crystals with prepared SWSs was increased 4.4% and 5.8% than as-grown ZnTe crystals, respectively. Simultaneously, the average transmittance in the range of 0.3–2.5 THz was improved ~15.4%. These findings inform an effective way to achieve ultrabroadband (from visible to terahertz) antireflection properties, which is favorable for further enhancing the THz generation and detection efficiency.