摘要
紫外光电探测器具有比可见和近红外光电探测器更低的背景噪声、更高的灵敏度和更强的抗干扰能力,广泛应用于光学成像、安全监测、空间探测等领域。近年来,窄禁带半导体微纳结构在紫外甚至日盲紫外探测领域脱颖而出。本文介绍了两类半导体微纳结构(超细纳米线、超薄纳米片)中光吸收特性随材料特征尺寸的变化,揭示了窄禁带半导体应用于紫外探测的工作机理,综述了基于窄禁带半导体微纳结构的紫外光电探测器的研究进展,并对发展趋势进行了展望。与宽禁带半导体和Si基紫外光电探测相比,窄禁带半导体微纳结构提供了一种工艺条件更简单、制造成本更低的紫外光电探测方式。
Ultraviolet(UV)photodetection is characterized by relatively lower background noise,higher sensitivity and stronger anti-interference capability than its visible and infrared counterparts,which greatly facilitate its application in fields including optical imaging,security monitoring and space-to-space communications.Photomultiplier tubes and Si photodetectors dominate the commercial UV photodetectors,which normally operate at high bias voltage or adopt elaborate filters to eliminate the effect of visible and near infrared spectra.Wide bandgap semiconductors with bandgap larger than 3.4 eV,such as AlGaN,SiC,ZnMgO and Ga2O3,are prominent candidates for highly sensitive UV photodetection due to their relatively high radiation hardness and intrinsic visible blindness.However,expensive apparatuses and intricate processes,such as Metal Organic Chemical Vapor Deposition(MOCVD),Molecular Beam Epitaxy(MBE),Plasma-Enhanced Chemical Vapor Deposition(PECVD),and highly corrosive and toxic chlorine(Cl2)-based dry Inductively Coupled Plasma Reactive Ion Etching(ICP-RIE),are normally required for the wide bandgap semiconductor technology.What is more,for the solar-blind photodetection,a higher concentration of Al(∼0.4)or Mg(∼0.5)will be needed to tune the bandgap up to 4.42 eV,which increases the difficulty in epitaxial growth of high-quality film.Phase segregation may occur in the film,introducing defects and dislocations and degrading the detecting performance.Therefore,development of a facile and effective strategy for UV photodetection remains challenging.Recently,narrow bandgap semiconductor nanostructures emerged in the field of UV or even solarblind UV photodetection.In this paper,we reviewed two kinds of nanostructures(nanowires and nanosheet)with the potential application in UV photodetection.Nanowires can be viewed as ultimately scaled-down versions of microcylinder resonators that can trap light in circulating orbits by multiple internal reflections from its boundary.Owing to their subwavelength size,the resonant modes in nanowires become leaky and interact more effectively with the outside world,carrying out a valuable antenna function.Different Leaky Mode Resonances(LMRs),including TM(Transverse Magnetic,HZ=0),TE(Transverse Electric,EZ=0),HE(magnetoelectric,TM-like),and EH(electromagnetic,TE-like)can be induced,which can selectively enhance the optical absorption in a particular spectral region and facilitate the tailoring of related optical absorption properties.When the illumination wavelength matched one of the allowed LMRs,there is an enhanced electromagnetic field in the nanowire.As a consequence,light absorption and the photocurrent could be enhanced at a desired wavelength by tuning the nanowire diameter.Horizontal nanowires tend to support TM and TE LMRs,the number of which reduces with the decrease of diameters.The wavelength corresponding to the specific leakage mode also decreases,resulting in a blue shift of the absorption peak.36 nm Si nanowires was found to be sensitive to UVB light and almost blind to visible and near-infrared illumination,showing peak absorption at 310 nm.For vertical nanowires,only HE1m transverse resonance modes result in absorption enhancements.The HE11 leaky mode is separated from the HE12 mode by a large spectral gap,which enables the high wavelength selectivity.When the diameter of Si nanowire decreases from 120 nm to 40 nm,the peak absorption due to the HE11 leaky mode resonance shifts to short wavelengths while the absorption attributable to the HE12 leaky mode begins to gradually weaken.By using Si nanowires array with a diameter of 45 nm as building blocks,a UV photodetector with peak absorption at 365 nm was fabricated.On the other hand,most semiconductors show wavelength-dependent absorption coefficient,which decreases with increasing wavelength.The short-wavelength incident light has a higher photon absorption rate on the top surface,which attenuates quickly when penetrating into the crystal,giving a smaller penetration depth(defined as the distance where the energy of incident light is reduced to 1/e of its initial value when it propagates in the medium),while the long-wavelength incident light has a larger penetration depth.Therefore,absorption of long-wavelength illumination can ben suppressed by thinning the crystal and the peak absorption blueshifts with the decreasing thickness,revealing the possibility of thinning narrow bandgap semiconductors for UV or even solar blind UV photodetection.Several kinds of nanosheets,including ultrathin Si etched from SOI,perovskite nanosheets grown by the space-confined method(MAPbBr3 and CsPbBr3 nanosheet)and Chemical Vapor Deposition(CVD)grown 2D layered semiconductors nanosheets(GaSe nanosheet),have been researched,all of which show UV sensitive photoresponse.The UV-to-visible rejection ratio increases gradually with the decrease of thickness.Further,simulation by Finite Element Method(FEM)reveals that through integration with an asymmetric Fabry-Pérot(F-P)resonator,selective absorption enhancement at the resonant wavelength can be realized and the UV-to-visible rejection ratio can be improved by about 2 orders of magnitude,comparable to that of the commercial GaN and SiC based Schottky photodiodes.Comparing to its wide bandgap semiconductor and Si-based counterparts,the narrow bandgap semiconductor-based photodetectors provide a filterless strategy for UV photodetection with easier manufacturing process and lower manufacturing cost.However,it still suffers from the poor detection performance such as lower UV-to-visible rejection ratio.The further research should focus on:1)improving the nanofabrication technology to uniformly control the characteristic parameters of semiconductors such as diameters and thickness for the stable and reliable photodetection;2)improving the manufacturing capability of integrated device to facilitate the application in fields including image sensing and real-time monitoring;3)combing with light regulation technology such as Localized Surface Plasmon Resonance(LSPR)and optical microcavity resonance to realize the highly selective absorption and therefore the high-performance UV photodetection.
作者
吴春艳
张宇梁
贺新辉
杨小平
王秀娟
WU Chunyan;ZHANG Yuliang;HE Xinhui;YANG Xiaoping;WANG Xiujuan(School of Microelectronics,Hefei University of Technology,Hefei 230009,China)
出处
《光子学报》
EI
CAS
CSCD
北大核心
2024年第7期31-41,共11页
Acta Photonica Sinica
基金
安徽省自然科学基金(No.2208085MF177)。
关键词
光电探测器
紫外
窄禁带半导体
泄漏模式共振
厚度依赖的吸收系数
Photodetector
Ultraviolet
Narrow bandgap semiconductor
Leaky mode resonance
Thickness-dependent absorption coefficient
