纳米多孔氮化铌薄膜红外宽带光响应特性

具有超导绝缘相变特性的纳米多孔超导薄膜在红外光电探测领域有着潜在的应用价值,而其在红外波段的宽带光响应特性研究目前尚未见报道.为此,本文以纳米多孔氮化铌(NbN)薄膜为主要对象,研究了其在780—5000nm的近、中红外波长范围内的光响应特性.首先,采用Drude模型拟合的方法,不仅将对实验数据拟合的精度提高了约17%,而且得到了中红外波段的NbN光学参数;进而,采用时域有限差分法分析了加载纳米多孔NbN薄膜的背面对光器件的光响应特性,并给出了能够将纳米多孔薄膜简化为均匀薄膜的Bruggeman等效模型,从而可以将纳米多孔NbN薄膜光响应特性的仿真维度由三维降为一维;最后,基于等效模型和传输矩阵法,对加载纳米多孔NbN薄膜的背面对光器件在近、中红外波段内的光吸收特性进行了优化设计.结果表明:一方面,使用Bruggeman等效模型简化设计过程并不会影响最终结果的正确性;另一方面,仅仅是加载较为简单的光学腔,即可使得探测器的薄膜光吸收率在近、中红外宽带设计时均大于82%,在近红外双波长设计时均大于93.7%,并且多孔薄膜结构具有天然的极化不敏感特性.

Infrared broadband photoresponse characteristics of nanoporous NbN film

Nanoporous superconducting films with superconductor-insulator transition characteristics have potential application in the field of infrared photoelectric detection,but their broadband optical response characteristics in infrared band have not been reported.Therefore,taking nanoporous niobium nitride(NbN)films as the main object,the optical response characteristics in the near and medium infrared wavelength range of 780–5000 nm are studied in this paper.Firstly,the Drude-model fitting accuracy of measured NbN permittivity is improved by about 17%,and the NbN optical parameters in mid-infrared band are obtained.Furthermore,the optical response characteristics of the back-illuminated device with nanoporous NbN film are analyzed by finite difference time domain method,and a Bruggeman equivalent model which can simplify the nanoporous film into a uniform film is given,thereby reducing the three-dimensional simulation of nanoporous NbN film into one dimensional simulation.Finally,based on the equivalent model and the transfer matrix method,the light absorption characteristics of the back-illuminated device in near-/mid-infrared wavelength ranges are optimized.The results indicate that,on the one hand,simplifying the design process by using Bruggeman equivalent model will not affect the correctness of the final optimization results,and,on the other hand,a relatively simple optical cavity can make the detector achieve polarization-independent film absorption greater than 82%for near-/mid-infrared broadband design and 93.7%for double-wavelength design.