Optical Thin Films with Very Low Refractive Index and Their Application in Photonics Devices

AbstractThe refractive index contrast in dielectric multilayer structures, optical resonators and photonic crystals is an important figure of merit, which creates a strong demand for high quality thin films with a very low refractive index. SiO2 nano-rod layers with low refractive indices n = 1.08, the lowest ever reported in thin-film materials, is grown by oblique-angle e-beam deposition of SiO2 with vapor incident angle 85 degree. Scanning electron micrographs reveal a highly porous columnar structure of the low-refractive-index (low-n) film. The gap between the SiO2 nano-rods is ≤50 nm, i.e. much smaller than the wavelength of visible light, and thus sufficiently small to make scattering very small. Optical micrographs of the low-n film deposited on a Si substrate reveal a uniform specular film with no apparent scattering. The unprecedented low index of the SiO2 nano-rod layer is confirmed by both ellipsometry measurements and thin film interference measurements. A single-pair distributed Bragg reflector (DBR) employing the SiO2 nano-rod layer is demonstrated to have enhanced reflectivity, showing the great potential of low-n films for applications in photonic structures and devices.

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Distributed Bragg reflector consisting of high- and low-refractive-index thin film layers made of the same material

Applied Physics Letters ◽

10.1063/1.2720269 ◽

2007 ◽

Vol 90 (14) ◽

pp. 141115 ◽

Cited By ~ 93

Author(s):

Martin F. Schubert ◽

J.-Q. Xi ◽

Jong Kyu Kim ◽

E. Fred Schubert

Keyword(s):

Thin Film ◽

Refractive Index ◽

Bragg Reflector ◽

Distributed Bragg Reflector ◽

Low Refractive Index

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OMNI-DIRECTIONAL REFLECTOR USING A LOW REFRACTIVE INDEX MATERIAL

International Journal of High Speed Electronics and Systems ◽

10.1142/s0129156404002740 ◽

2004 ◽

Vol 14 (03) ◽

pp. 726-731

Author(s):

J.-Q. XI ◽

MANAS OJHA ◽

WOOJIN CHO ◽

TH. GESSMANN ◽

E. F. SCHUBERT ◽

...

Keyword(s):

Refractive Index ◽

Dielectric Material ◽

Metal Layer ◽

Transverse Magnetic ◽

Bragg Reflector ◽

Light Extraction Efficiency ◽

Distributed Bragg Reflector ◽

Triple Layer ◽

Quarter Wavelength ◽

Low Refractive Index

Triple-layer omni-directional reflectors (ODRs) consisting of a semiconductor, a transparent quarter-wavelength dielectric layer and metal layer have high reflectivities at all angles of incidence. In this paper, triple-layer ODRs are demonstrated that incorporate nanoporous SiO 2, a novel low-refractive-index (low-n) material with refractive indices n ≪ 1.46 as well as dense SiO 2 (n = 1.46). GaP and Ag serve as the semiconductor and metal layer materials, respectively. An angle-integrated transverse electric (TE) mode reflectivity of R avg | TE = 99.9 % and transverse magnetic (TM) mode reflectivity R avg | TM = 98.9 % are calculated for the triple-layer ODRs employing nanoporous SiO 2. Reflectivity measurements, including the angular dependence of R, are presented. Novel hybrid ODRs consisting of semiconductor, a several micron thick low-n dielectric material layer, a distributed Bragg reflector (DBR) and metal layer have outstanding reflectivities for all incident angles. GaP and Ag serve as the semiconductor and metal layer, respectively. Nanoporous SiO 2 is used as the low-n material. TiO 2 and dense SiO 2 serve as the DBR materials. The angle-intergrated reflectivities of the TE and TM modes are calculated to be larger than 99.9 % for the hybrid ODRs. The results indicate the great potential of the ODRs for light-emitting diodes with high light extraction efficiency.

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Synthesis, Crystallography, Microstructure, Crystal Defects, Optical and Optoelectronic Properties of ZnO:CeO2 Mixed Oxide Thin Films

Photonics ◽

10.3390/photonics7040112 ◽

2020 ◽

Vol 7 (4) ◽

pp. 112

Author(s):

Qais M. Al-Bataineh ◽

Mahmoud Telfah ◽

Ahmad A. Ahmad ◽

Ahmad M. Alsaad ◽

Issam A. Qattan ◽

...

Keyword(s):

Thin Film ◽

Thin Films ◽

Refractive Index ◽

Mixed Oxide ◽

Visible Region ◽

Functional Materials ◽

Crystal Defects ◽

Optoelectronic Properties ◽

Oxide Thin Films ◽

Pure Ceo2

We report the synthesis and characterization of pure ZnO, pure CeO2, and ZnO:CeO2 mixed oxide thin films dip-coated on glass substrates using a sol-gel technique. The structural properties of as-prepared thin film are investigated using the XRD technique. In particular, pure ZnO thin film is found to exhibit a hexagonal structure, while pure CeO2 thin film is found to exhibit a fluorite cubic structure. The diffraction patterns also show the formation of mixed oxide materials containing well-dispersed phases of semi-crystalline nature from both constituent oxides. Furthermore, optical properties of thin films are investigated by performing UV–Vis spectrophotometer measurements. In the visible region, transmittance of all investigated thin films attains values as high as 85%. Moreover, refractive index of pure ZnO film was found to exhibit values ranging between 1.57 and 1.85 while for CeO2 thin film, it exhibits values ranging between 1.73 and 2.25 as the wavelength of incident light decreases from 700 nm to 400 nm. Remarkably, refractive index of ZnO:CeO2 mixed oxide-thin films are tuned by controlling the concentration of CeO2 properly. Mixed oxide-thin films of controllable refractive indices constitute an important class of smart functional materials. We have also investigated the optoelectronic and dispersion properties of ZnO:CeO2 mixed oxide-thin films by employing well-established classical models. The melodramatic boost of optical and optoelectronic properties of ZnO:CeO2 mixed oxide thin films establish a strong ground to modify these properties in a skillful manner enabling their use as key potential candidates for the fabrication of scaled optoelectronic devices and thin film transistors.

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Optimized Thin-Film Organic Solar Cell with Enhanced Efficiency

Sustainability ◽

10.3390/su132313087 ◽

2021 ◽

Vol 13 (23) ◽

pp. 13087

Author(s):

Waqas Farooq ◽

Muhammad Ali Musarat ◽

Javed Iqbal ◽

Syed Asfandyar Ali Kazmi ◽

Adnan Daud Khan ◽

...

Keyword(s):

Thin Film ◽

Solar Cell ◽

Organic Solar Cell ◽

Short Circuit ◽

Short Circuit Current ◽

Short Circuit Current Density ◽

Open Circuit ◽

Bragg Reflector ◽

Performance Parameters ◽

Distributed Bragg Reflector

Modification of a cell’s architecture can enhance the performance parameters. This paper reports on the numerical modeling of a thin-film organic solar cell (OSC) featuring distributed Bragg reflector (DBR) pairs. The utilization of DBR pairs via the proposed method was found to be beneficial in terms of increasing the performance parameters. The extracted results showed that using DBR pairs helps capture the reflected light back into the active region by improving the photovoltaic parameters as compared to the structure without DBR pairs. Moreover, implementing three DBR pairs resulted in the best enhancement gain of 1.076% in power conversion efficiency. The measured results under a global AM of 1.5G were as follows: open circuit voltage (Voc) = 0.839 V; short circuit current density (Jsc) = 10.98 mA/cm2; fill factor (FF) = 78.39%; efficiency (η) = 11.02%. In addition, a thermal stability analysis of the proposed design was performed and we observed that high temperature resulted in a decrease in η from 11.02 to 10.70%. Our demonstrated design may provide a pathway for the practical application of OSCs.

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Optical Properties of Alq3/TiO2 BDR Structure Processed by Spin Coating Technique

MRS Advances ◽

10.1557/adv.2019.22 ◽

2019 ◽

Vol 4 (11-12) ◽

pp. 661-666

Author(s):

L. Ajith DeSilva ◽

Sarahn Nazaret ◽

A. G. U. Perera ◽

T. M. W. J. Bandara

Keyword(s):

Thin Films ◽

Titanium Dioxide ◽

Optical Properties ◽

Band Gap ◽

Spin Coating ◽

Light Emission ◽

Wide Band ◽

Bragg Reflector ◽

Distributed Bragg Reflector ◽

Pl Quenching

ABSTRACTOne-dimensional hybrid Distributed Bragg Reflector (DBR) is constructed using Tris (8-hydroxy) quinoline aluminum (Alq3) molecules and Titanium dioxide (TiO2) nanoparticles via spin coating process. Light emission from thin films of low molecular weight organic semiconductor of Alq3 is dominated by excitons. This material has been widely used as a superior emitter for organic light emitting diodes. Titanium dioxide (TiO2) is an inorganic semiconductor with a high band gap. Photoluminescence (PL) of thin films of Alq3 showed a broad PL peak at 530 nm. In DBR structures, PL quenching is observed but there is no shift in the PL peak of the Alq3. The PL quenching is tentatively attributed to energy transfer via sensitization to wide band gap TiO2 layers. A simple excitonic model is suggested to explain the observation. Fabrication process and optical properties of the structure are presented.

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