Design of midinfrared photodetectors enhanced by surface plasmons on grating structures
Design of midinfrared photodetectors enhanced by surface plasmons on grating structures
复制标题
DOI：
10.1063/1.2360896
复制
发表时间：
2006-10
影响因子：
4
通讯作者：
Zongfu Yu;G. Veronis;S. Fan;M. Brongersma
中科院分区：
文献类型：
--
作者：
Zongfu Yu;G. Veronis;S. Fan;M. Brongersma
作者建议利用表面等离子激元的独特性质来提高中红外光电探测器的信噪比。提出的光电探测器由金属平板上的狭缝组成，其中填充了可吸收的半导体材料。由于法布里-珀罗共振，狭缝中的光吸收得到了增强。进一步的吸收增强是通过在狭缝周围环绕一系列周期性凹槽来实现的，这些凹槽能够激发表面等离子激元，将电磁能量输送到狭缝中。利用这一方案，他们设计并优化了一种工作在0=9.8m的光电探测器，与工作在相同波长的传统光电探测器相比，单位体积半导体材料的吸收大约增加了250倍。©2006美国物理研究所。DOI：10.1063/1.2360896工作在10米波长附近的中红外探测器和成像系统在从夜视到天文学研究的各种应用中都很重要。1为了抑制热波动引起的噪声，通常需要对这些检测系统进行冷却1-3，这大大增加了成本，限制了可移植性。为了提高信噪比，希望在不影响吸收的光功率的情况下减小产生噪声的有源探测器的体积。在这封信中，我们通过计算探索在这些系统中使用表面等离子激元来提高信噪比。所提出的结构，如图1a所示，由一个金属狭缝组成，周围环绕着一个线性栅格结构。整个结构被放置在绝缘氧化物的顶部。狭缝填充了可吸收的半导体材料，其宽度远远小于工作波长。金属区域既是电触点，又是聚光器，将光线导入深亚波长狭缝。4-6为了最大化集中效应，我们结合了两种不同的机制，这两种机制与狭缝的存在和栅格结构有关。7即使当狭缝的宽度是深亚波长尺度时，金属狭缝也支持传播TE模。此外，由于缝隙中的模式与自由空间传播波之间存在很强的阻抗失配，因此在缝隙入口处会产生强烈的反射。因此，在适当选择长度的情况下，狭缝形成法布里-珀罗谐振腔，狭缝中的光吸收得到共振增强。另一方面，通过将入射的电磁波转换为金属表面上的表面等离子激元，可以将其输送到狭缝中，从而增强了狭缝中的光吸收。8收集电磁能量的区域可以比狭缝宽度大得多，从而显著增强吸收的能量。通过仔细选择结构的几何参数，可以使这两种机制发生在同一波长，从而实现器件的最佳效率。为了模拟这种结构对垂直入射的电磁平面波的响应，我们使用了一种二维有限差分频域方法，9，10，它直接使用了金等金属的介电常数随频率变化的实验数据，11包括实部和虚部，没有进一步的近似。对于狭缝中的探测材料，我们选择了频率无关介电常数=12.5+i1.75的HgCdTe MCT。2，11衬底是低折射率的氧化物
The authors propose to exploit the unique properties of surface plasmons to enhance the signal-to-noise ratio of midinfrared photodetectors. The proposed photodetector consists of a slit in a metallic slab filled with absorptive semiconductor material. Light absorption in the slit is enhanced due to Fabry-Perot resonances. Further absorption enhancement is achieved by surrounding the slit with a series of periodic grooves that enable the excitation of surface plasmons that carry electromagnetic energy towards the slit. Using this scheme, they design and optimize a photodetector operating at 0=9.8 m with a roughly 250 times enhancement in the absorption per unit of volume of semiconductor material compared to conventional photodetectors operating at the same wavelength. © 2006 American Institute of Physics. DOI: 10.1063/1.2360896 Midinfrared photodetectors and imaging systems operating in the vicinity of 10 m wavelength are important in applications ranging from night vision to astronomy research. 1 To suppress noise caused by thermal fluctuation, usually these detection systems have to be cooled, 1‐3 which greatly increases the cost and limits the portability. To improve signal/noise ratio, it is desirable to reduce the active detector volume from which the noise arises without affecting the absorbed light power. In this letter, we computationally explore the use of surface plasmons in these systems to improve the signal/noise ratio. The proposed structure, shown in Fig. 1a, consists of a metallic slit, surrounded by a linear grating structure. The entire structure is placed on top of an insulating oxide. The slit is filled with absorptive semiconductor material, and has a width that is far smaller than the operating wavelength. The metal regions serve both as electrical contacts and as a concentrator that funnels light into the deep-subwavelength slit. 4‐6 To maximize the concentration effects, we combine two distinct mechanisms that relate to the presence of the slit and the grating structure. 7 A metal slit supports a propagating TE mode, even when the width of the slit is at deepsubwavelength scales. Moreover, due to the strong impedance mismatch between the modes in the slit and free-space propagating waves, strong reflection can occur at the entrances to the slit. Consequently, with an appropriate choice of the length, the slit forms a Fabry-Perot resonator, and light absorption in the slit is resonantly enhanced. The grating, on the other hand, enhances the light absorption in the slit by converting incident electromagnetic EM waves into surface plasmons on the metal surface that can be funneled into the slit. 8 The area from which EM energy is collected can be substantially larger than the slit width and gives rise to significant enhancements in the absorbed energy. With a careful choice of the geometric parameters of the structure, these two mechanisms can be made to occur at the same wavelength, resulting in an optimized efficiency of the devices. To simulate the response of this structure for a normally incident EM plane wave, we use a two-dimensional finitedifference frequency-domain method, 9,10 which directly uses experimental data for the frequency-dependent dielectric constant of metals such as gold, 11 including both the real and imaginary parts, with no further approximation. For the detective materials in the slit, we have chosen to use HgCdTe MCT with a frequency independent dielectric permittivity of =12.5+i1.75. 2,11 The substrate is a low-index oxide