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Bias-dependent spectral tuning in InP nanowire-based photodetectors
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and Nano, Lund University, Lund, Sweden. (Nanovetenskap)ORCID iD: 0000-0001-5993-8106
Solid State Physics and Nano, Lund University, Lund, Sweden. (Nanometerkonsortiet)
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and Nano, Lund University, Lund, Sweden. (Nanovetenskap)ORCID iD: 0000-0002-3160-8540
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and Nano, Lund University, Lund, Sweden. (Nanovetenskap)
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2017 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 28, no 11, article id 114006Article in journal (Refereed) Published
Abstract [en]

Nanowire array ensembles contacted in a vertical geometry are extensively studied and considered strong candidates for next generations of industrial scale optoelectronics. Key challenges in this development deal with optimization of the doping profile of the nanowires and the interface between nanowires and transparent top contact. Here we report on photodetection characteristics associated with doping profile variations in InP nanowire array photodetectors. Bias-dependent tuning of the spectral shape of the responsivity is observed which is attributed to a Schottky-like contact at the nanowire-ITO interface. Angular dependent responsivity measurements, compared with simulated absorption spectra, support this conclusion. Furthermore, electrical simulations unravel the role of possible self-gating effects in the nanowires induced by the ITO/SiOx wrap-gate geometry. Finally, we discuss possible reasons for the observed low saturation current at large forward biases.  

Place, publisher, year, edition, pages
Bristol: Institute of Physics Publishing (IOPP), 2017. Vol. 28, no 11, article id 114006
Keywords [en]
nanowires, nanowire arrays, IR photodetectors, solar cells, nanophotonics
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:hh:diva-32769DOI: 10.1088/1361-6528/aa5236ISI: 000395937500001Scopus ID: 2-s2.0-85014564717OAI: oai:DiVA.org:hh-32769DiVA, id: diva2:1058350
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2018-04-25Bibliographically approved
In thesis
1. Tailoring the Optical Response of III-V Nanowire Arrays
Open this publication in new window or tab >>Tailoring the Optical Response of III-V Nanowire Arrays
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Semiconductor nanowires show a great deal of promise for applications in a wide range of important fields, including photovoltaics, biomedicine, and information technology. Developing these exciting applications is strongly dependent on understanding the fundamental properties of nanowires, such as their optical resonances and absorption spectra. In this thesis we explore optical absorption spectra of arrays of vertical III-V nanowires with a special emphasis on structures optimized to enhance absorption in the solar spectrum. First, we analyze experimentally determined absorption spectra of both indium phosphide (InP) and gallium phosphide (GaP) nanowire arrays. The study provides an intuitive understanding of how the observed absorption resonances in the nanowires may be tuned as a function of their geometrical parameters and crystal structure. As a consequence, the spectral position of absorption resonances can be precisely controlled through the nanowire diameter. However, the results highlight how the blue-shift in the optical absorption resonances as the diameter of the nanowires decreases comes to a halt at low diameters. The stop point is related to the behavior of the refractive indices of the nanowires. The wavelength of the stop is different for nanowire polytypes of similar dimensions due to differences in their refractive indices. We then present a theoretical argument that it is important to consider symmetry properties when tailoring the optical modes excited in the nanowires for enhanced absorption. We show that absorption spectra may be enhanced compared to vertical nanowires at normal incidence by tilting the nanowires with normal incidence light, or by using off-normal incidence with vertical nanowires. This is because additional optical modes inside the nanowires are excited when the symmetry is broken. Looking forward to omnidirectional applications, we consider branched nanowires as a way to enhance the absorption spectra at normal incidence by taking advantage of simultaneous excitation of the spectrally different optical modes in the branches and the stems. Third, we describe in theoretical terms how integrating distributed Bragg reflectors (DBRs) with the nanowires can improve absorption spectra compared to conventional nanowires. DBRs provide a way to employ light trapping mechanisms which increases the optical path length of the excited modes and thereby improves the absorption of the excited modes. At normal incidence, DBR-nanowires improve the absorption efficiency to 78%, compared to 72% for conventional nanowires. We show that the efficiency is increased to 85% for an off-normal incident angle of 50˚. Overall, our results show that studies of optical resonances in nanowires that take the light-matter interaction into account provide opportunities to develop novel optical and optoelectronic functionalities in nanoscience and nanotechnology.

Place, publisher, year, edition, pages
Lund: Lund University, 2017. p. 63
Keywords
III-V nanowires, absorption, optical modes, photovoltaics
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:hh:diva-36683 (URN)978-91-7753-277-4 (ISBN)978-91-7753-278-1 (ISBN)
Public defence
2017-06-02, Rydbergsalen, Fysicum, Sölvegatan 14, Lund, 13:15 (English)
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Supervisors
Available from: 2018-05-03 Created: 2018-04-25 Last updated: 2018-05-03Bibliographically approved

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Jain, VishalKarimi, MohammadHussain, LaiqPettersson, Håkan

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