Controlled and Selective Growth of 1D and 3D CdTe Nanostructures through a Structurally Engineered Porous Alumina Template for Enhanced Optical Applications

Abstract

Current manuscript describes porous alumina (PA) template assisted electrodeposition of high aspect ratio nanowires and dense hierarchical structures of CdTe. We demonstrate here for the first time that simple structural engineering of a PA template can lead to electrochemical growth of diverse shapes of CdTe nanostructures. Facile and cost-effective modifications have been implemented for the fabrication of self-organized through-hole PA membrane and its transfer onto any rough substrate. These modifications have facilitated extended duration (30 minute to 1 hour) electrodeposition of CdTe nanostructures at high bath temperature of 60 • C without delaminating the PA membrane. High aspect ratio nanowires of 60 nm diameter and 2.8 μm length were growth through the self-ordered PA membrane without any underlying metal coating i.e. without altering its optical properties. An average of 56% optical absorption (within 350 nm -1400 nm wavelength) and a moderate photoluminescence was observed for the CdTe nanowires. Minor variation in the anodization process resulted into a non-uniform/branched PA template that enabled the formation of dense 3D hierarchical structures of CdTe using similar electrodeposition conditions as that used for CdTe nanowires. The hierarchical CdTe nanostructures exhibited very high total optical absorption of ∼90% within 350 nm -1400 nm wavelength and a strong photoluminescence was also demonstrated that was almost 10 fold more intense than the CdTe nanowires. CdTe, CdS, CdSe are well established II-VI periodic group optically active chalcogenide semiconductor materials with immense applications in optoelectronic, photonics and bio-labelling applications. Intervention of Nanoscience and Nanotechnology has enabled realization of low dimensional nanostructures of Cadmium chalcogenides (CdS, CdSe, or CdTe) with enhanced surface area to volume ratio that have attracted major appreciation with their unique and enhanced electronic and optical properties.1-3 Specifically, 1D Cadmium chalcogenide nanowires/nanorods have demonstrated highperformance optoelectronic applications such as optical waveguides, lasers, photoluminescence, photodetectors (visible, NIR), solar cells, etc. [4][5][6][7][8][9][10][11][12][13][14][15] It is realized that a precise control over the size and the structure of nanostructures enables vast tuning of the energy band gaps and generates unique optical properties.16 Unlike 2D structures, nanowires can accommodate large amount of mismatch related strain via radial expansion or contraction. It is known that nanowires with high aspect ratio can provide efficient absorption even with smaller depth that can increase the efficacy of photovoltaic devices.17 Especially, CdTe nanowires holds potential for low-cost photovoltaic due to its high absorption coefficient, with a capability of absorbing significant amount of sunlight in a layer thickness of only ∼1 μm, as compared to ∼10 μm for Si. Overall, it is apparent that there has been a major focus onto controlling the structural param...

Revisiting anodic alumina templates: from fabrication to applications

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