Research progress of artificial microstructure thin layer infrared detector (Invited)
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摘要: 薄层的红外探测材料虽然能够保持很好的均匀性,减少了红外探测时的噪音,但由于薄层红外探测材料体积偏小,限制了红外探测器的吸收。针对不同红外探测材料的特点,利用人工微结构能够有效地改善红外探测器的性能。文中介绍了增强薄层红外探测材料吸收的策略,分别是使用金属背板、金属光栅结构和非对称F-P型金属腔体结构, 它们在各自适应的场景下都能取得不错的效果。同时也简略地介绍了人工微结构调控吸收峰高和峰宽的机理。并且展示了人工微结构在几种红外探测器件上的应用。最后,提出了一种人工微结构碲镉汞红外探测器的设计,实现了在3.5~5.5 μm大气窗口内的宽频吸收, 其中吸收峰的高度为91.8%,吸收峰的相对宽度为41.8%,在大气窗口内的大部分频率,增强系数均大于6。人工微结构的发展开拓了传统红外器件的设计思路,为新型的红外器件提供了理论依据和指导。Abstract: The thin layer of infrared detection material guarantees the uniformity of the materials and reduces the signal noise in infrared detection. The absorption of infrared detector is limited by the thin layer of infrared detection material attributing to small volume. According to the characteristics of different infrared detection materials, artificial microstructure can effectively improve the performance of infrared detector. The strategies of enhancing the absorption of thin-layer infrared detection materials were introduced. The strategies were based on metal back plate, metal grating and asymmetric Fabry-Perot cavity. They could have an excellent performance in their own adaptive scenarios. Meanwhile, the mechanism of adjusting the absorption peak height and width by artificial microstructure was also elaborated briefly. The application of artificial microstructure in several infrared detectors was demonstrated. Finally, an artificial microstructure HgCdTe infrared detector was designed, which could achieve broadband absorption in 3.5-5.5 μm atmospheric window. The absorption peak reached 91.8% and the relative peak width was 41.8%. In most of frequency in the atmospheric window, the absorption enhancement is higher than 6. The development of artificial microstructure opens up the design idea of traditional infrared devices, and provides theoretical basis and guidance for new infrared devices.
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Key words:
- artificial microstructure /
- metamaterial /
- infrared detector
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图 1 增强薄层红外探测材料吸收的三种人工微结构。 (Ⅰ)无结构, (Ⅱ)后端增加金属膜作为反射镜, (Ⅲ)前端增加金属光栅, (Ⅳ)非对称F-P共振腔结构
Figure 1. Three kinds of artificial microstructures for enhancing absorption of thin layer infrared detection materials. (Ⅰ) Unstructured, (Ⅱ) metal film as perfect mirror behind thin layer, (Ⅲ) metal grating in front of thin layer, (Ⅳ) asymmetric Fabry-Perot resonant cavity
图 2 (a)增强薄层红外探测材料吸收的策略;(b)一般共振的示意图;(c)人工微结构HgCdTe红外探测器吸收的机理:①利用F-P腔模增强时,电场强度|Ey|的分布; ②利用表面等离激元增强时,电场强度|Ey|的分布。截面为如绿色方块所示的x-y平面,截面中的金属部分由白色虚线框出。Δ/a=0.75,λ0=3.9 μm,t3= 310 nm。 ① 中计算结构Ⅳ;② 中计算结构Ⅲ,其余的参数一致
Figure 2. (a) Strategies for enhancing absorption of thin layer infrared detection materials; (b) Schematic diagram of general resonance; (c) Absorption mechanism of HgCdTe infrared detector with artificial microstructure: ① Distribution of |Ey| in structure Ⅳ, which is obviously concentrated in F-P cavity; ② Distribution of |Ey| in structureⅢ, which is concentrated in the SPP. The sections are the x-y plane as shown as green square, and the metal part in the sections is framed by the white dotted line. Δ/a = 0.75,λ0 = 3.9 μm,t3 = 310 nm
图 3 非对称F-P共振腔人工微结构红外器件的结构图。(a)超材料完美吸收器[21]。最上层为十字形金属谐振器阵列,十字的长度为l,宽度为w,周期长度为a,最下层为金属的接地层;(b)量子点(阱)红外探测器和设计的高效宽频HgCdTe红外探测器结构[22, 23-24]。最上层为金属光栅,最下层为金属薄膜,金属光栅既可以是一维光栅,也可以是二维光栅。光栅的周期为a,镂空部分的长度为Δ。金属光栅层的厚度为t1,金属薄膜层的厚度为t4,探测介质(MCT)层的厚度为t3
Figure 3. Schematic of asymmetric Fabry−Perot cavity artificial microstructures infrared device. (a) Perfect metamaterial absorber [21]. The top layer is array of cross resonators, which has length l, width w and period a, the bottom layer is the ground plane; (b) Schematic of quantum dot (well) infrared detector and HgCdTe infrared detector with high-efficiency and broadband [22, 23-24]. The top layer is metal grating and the bottom layer is metal film. Metal grating can be 1D grating or 2D grating. The period of grating is a and the length of hollow part is Δ. The thickness of metal grating layer, metal film layer and detection medium (MCT) layer is t1, t4 and t3, respectively
图 4 (a) ①③二维光栅,②④一维光栅,参考文献[22]的量子点红外探测器吸收情况。①和②各层的吸收情况,③和④不同入射角有源层的吸收情况。a = 2 μm,Δ/a = 0.7,t1 = t4 = 0.1 μm,t2 = 0.3 μm;(b)参考文献[24]的量子阱红外探测器的①各层吸收率, ②理想量子阱(点)、实际量子阱和用砷化镓光栅取代金光栅结构的吸收增强系数。a = 4.6 μm,Δ/a = 0.5,t1 = t2 = 0.2 μm,t3 = 0.4 μm;(c)参考文献[25]的包覆减反层的量子阱红外探测器的① 各层吸收率, ② IQW (黑实线)和RQW (蓝虚线)的吸收增强系数。参数与(b)相同,tc = 1.2 μm
Figure 4. (a) Absorption of QD infrared detector in Ref. [22] with ①③2D grating, ②④1D grating. ①② Absorption in different layer, ③④absorption in active layer with different incident angle. a = 2 μm,Δ/a = 0.7, t 1 = t 4 = 0.1 μm, t 2 = 0.3 μm; (b) Absorption of QW infrared detector in Ref. [24]. ① Absorptivity in different layer, ② absorption enhancement with different structure (IQD, IQW, RQW and GaAs grating). a = 4.6 μm,Δ/a = 0.5,t1 = t2 = 0.2 μm,t3 = 0.4 μm; (c) Absorption of QW infrared detector with antireflection layer in Ref. [25]. ① Absorptivity in different layer, ②absorption enhancement of IQW(black line) and RQW(blue dash line). The parameters is the same as (b) but tc =1.2 μm
图 5 人工微结构HgCdTe红外探测器中厚度不同的MCT层在3~6 μm波段的吸收谱。金光栅层和金属薄膜层中的金属与介质的边界采用完美电导体边界,不计厚度。Δ/a = 0.75. (a)结构Ⅰ,(b)结构Ⅱ,(c)结构Ⅲ,(d)结构Ⅳ
Figure 5. Absorption spectra of artificial microstructure HgCdTe infrared detector with different thickness of MCT layer in 3-6 μm. The interface of metal grating (metal film) and dielectric adopt perfect electric conductor (PEC) boundaries. The thickness of metal grating and metal film is ignored. Δ/a = 0.75 is set. Calculation for structure (a)Ⅰ, (b)Ⅱ, (c)Ⅲ, (d)Ⅳ
图 6 (a)人工微结构HgCdTe红外探测器中厚度为310 nm的MCT层在3~6 μm波段的吸收谱(红线)、总吸收谱(黑线)和吸收增强系数(橙虚线)。绿线为相同厚度无人工微结构的MCT层的吸收谱线,吸收增强系数为MCT层吸收与无人工微结构MCT层吸收的比值。金光栅层和金属薄膜层的介电常数采用Drude模型,Δ/a = 0.82; (b)二维金属光栅的参数Δ/a对MCT层吸收的影响
Figure 6. (a) The absorption spectrum of MCT layer (red line), total absorption spectrum (black line) and absorption enhancement coefficient (orange dotted line) in the artificial microstructure HgCdTe infrared detector at 3-6 μm wavelength, the thickness of MCT layer is 310 nm. The green line is absorption spectrum of MCT layer without artificial microstructure with the same thickness. The absorption enhancement coefficient is defined as the ratio of MCT layer absorption to reference (green line). The dielectric constant of gold grating layer and gold film layer is described by Drude model, Δ/a = 0.82. (b) The relationship between Δ/a of two dimensional metal grating and absorption of MCT layer
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