Accurate analysis of the piezopotential and the stored energies in laterally bent piezo-semiconductive NWs
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Accurate analysis of the piezopotential and the stored energies in laterally bent piezo-semiconductive NWs Rodolfo Araneo1*, Giampiero Lovat1, Christian Falconi2,3, Andrea Notargiacomo4, Antonio Rinaldi5,6 1
DIAEE - Sapienza University of Rome, Via Eudossiana 18, 00184, Rome Department of Electronic Engineering, University of Rome “Tor Vergata”, Via del Politecnico 1, 00133, Rome 3 CNR IDASC, Via Fosso del Cavaliere, 100, 00133 Rome, Italy 4 Institute of Photonics and Nanotechnology – CNR, Via Cineto Romano 42, 00156, Rome , Italy 5 University of L'Aquila, International Research Center for Mathematics & Mechanics of Complex System (MEMOCS), Via S. Pasquale, 04012, Cisterna di Latina (LT), Italy 6 ENEA ,C.R. Casaccia, Via Anguillarese 301, Santa Maria di Galeria, 00123, Rome, Italy 2
ABSTRACT Here we study the piezopotential, the carrier concentration, and the stored energies in laterally bent piezo-semiconductive NWs with total-bottom contact. Moreover, we give reasons for the well-known existence of two regions where the piezopotential has an opposite sign in comparison with the rest of the NW. Finally, we provide an upper limit to the static mechanicalto-electrical conversion efficiency by computing the ratio between the total stored electrostatic energy and the total (mechanical and electrostatic) stored energy. Our results can provide guidelines for designing devices based on laterally bent piezoelectric NWs. INTRODUCTION Quasi-1D piezoelectric nanodevices are being intensively studied for sensing, energy harvesting, piezotronics, piezophototronics, and more [1-8]. For these reasons, the piezopotential within laterally bent nanowires (NWs) has been investigated, even taking into account the effect of free electron charges, in several previous works [9-12]. Nevertheless, a few important phenomena in laterally bent piezo-semiconductive NWs have not yet been explained. First, at the base of laterally deflected NWs there are two regions which exhibit an inverted piezopotential in comparison with the rest of the NW; though such inverted regions have been extensively reported [1,9-12], no explanation could be found in literature. Second, the only previous report containing the calculation of the stored electrostatic energy in a laterally bent piezoelectric NW [12] has not taken into account the free charge carriers which are unavoidably present in piezosemiconductive NWs (e.g. ZnO NWs). Finally, though the parameter ξ [12], i.e. the ratio between the total stored electrostatic energy and the total (mechanical and electrostatic) stored energy, represents an upper limit to the static mechanical-to-electrical conversion efficiency, in literature there is no analysis on the value of ξ in laterally deflected NWs. Here we take advantage of FEM simulations for calculating the piezopotential, the charge concentration, the stored energies, and ξ in laterally deflected piezo-semiconductive NWs; moreover, we give reasons for the inversion of the sign of the piezopotential at the base of the NW. Our calculations fully take into
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