### 硒化锌衬底表面仿生宽带增透微结构的设计及制作

Design and Fabrication of Bionic Broadband Antireflective Microstructure on Zinc Selenide

#### 3中国科学院大学, 北京 100049

Abstract
The optical properties of parabolic cone array microstructure of zinc selenide are researched by finite-difference time-domain method. The effects of microstructure parameters, such as period, height, filling factor, and profile shape on the reflectivity are discussed. Structural parameters corresponding to good antireflection effect are obtained. The parabolic cone period microstructure is prepared by twice interference lithography and reactive ion etching technology according to the simulated results. The surface morphology is analyzed by field emission scanning electron microscopy, and the transmittances of the zinc selenide with double-sides polished and single-side microstructures are respectively measured with the utilization of the Fourier transform infrared spectrometer. The measured results illustrate that the average transmittance of samples with single-sided microstructure is 10% higher than that of double-sided polished zinc selenide at 2-5 μm wavelengths, and the transmittance reaches a maximum value of 82% at 2.3 μm.

## 2 微结构的设计与模拟

Stavenga等[18]认为抛物线锥微结构比圆锥和高斯钟形渐变微结构具有更好的减反射性能,抛物锥体周期阵列结构示意图如图1所示。模拟分析的微结构模型采用抛物锥体结构,并按一定的周期正交排列,周期为Λ,抛物锥体底面直径为d,结构高度为H。描述电磁场传播特性的数学模型主要有等效介质理论(EMT)[19]、时域有限差分法(FDTD)[20]、传递矩阵法(TMM)[21]、严格耦合波法(RCWA)[22]和有限元法(FEM)[23]等。当周期结构的尺寸远小于入射波长时,周期结构的光栅可以等效为均匀介质。当光入射到具有周期结构的表面时,在周期结构上发生的衍射满足光栅方程[24]:

$nssinθT=mλ0Λ+nisinθI,(1)$

$Λλ0<1max(ns,ni)+nisinθI。(2)$

## 4 实验结果与分析

#### Table 1. Comparison between theoretical design and experimental results

ParameterMaximum reflectivity /%Average transmittance /%Height /nmPeriod /nmFilling factor
Design value<481.81000±50800±201.0
Experimental value<580.910318001.0

#### Fig. 9. Curves of transmittance. (a) With and without microstructure; (b) simulated and experimental results

2~5 μm波段内的平均透过率超过了80.9%,整体透过率提高了10%左右,在2.3 μm处的最大透过率为82%,接近单面透过率的理论最大值。同时,根据实验结果和理论分析可以计算出单面制备有微结构样品的表面最大反射率为5%。

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