Electromechanical Fields in Piezoelectric Semiconductor Nanofibers under an Axial Force
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Electromechanical Fields in Piezoelectric Semiconductor Nanofibers under an Axial Force C.L. Zhang1,2,3,*, Y.X. Luo1, R.R. Cheng1 and X.Y. Wang1 1 Department of Engineering Mechanics, Zhejiang University, Hangzhou, 310027, China 2 Soft Matter Research Center (SMRC), Zhejiang University, Hangzhou, 310027, China 3 Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Hangzhou, 310027, China ABSTRACT Piezoelectric semiconductors (PS) nanofibers, which simultaneously exhibit piezoelectricity and unique electric conductive behavior, have huge applications in sensors, energy harvesters, and piezoelectric field effect transistors. Electromechanical fields and charge carrier in PS nanofibers can be effectively controlled by a mechanical force. One-dimensional linear equations for PS nanofibers, which are suitable for small axial force and small electron concentration perturbation, are presented. Analytical expressions for the electromechanical fields and electron concentration in the fiber are obtained. Numerical results show that the electromechanical fields near the two ends are sensitive to the initial electron concentration and the applied axial force. INTRODUCTION Piezoelectric semiconductor (PS) materials and structures have found wide range applications in multi-functional electronic devices due to the unique synergy of piezoelectric and semiconducting properties [1]. The interaction between the piezoelectric potential and the charge carrier in PS materials and structures under a bias voltage or mechanical force, makes them exhibit a variety of novel mechanical, electronic, and optical behaviors. Relatively recently, various one-dimensional (1D) PS nanostructures have been synthesized, such as ZnO fibers, tubes, belts and spirals [2-4]. They can be made into single structures [5-8] or in arrays [9-12], and have been used to make energy harvesters for converting mechanical energy into electrical energy [13-17], piezoelectric field effect transistors [2, 3, 18] operated by mechanical fields, acoustic charge transport devices [19], and strain, gas, humidity and chemical sensors [2, 20]. A mechanical force can be utilized to effectively control and tune the properties of PS structures. For example, the external strain-induced piezoelectric potential can be as a ‘gate’ voltage [1], and can be used to improve the performance of optoelectronic devices [6]. It is important to theoretically comprehend the electromechanical behaviors of 1D PS structures under external stimuli for their applications in devices. There are many experimental and modeling investigations on 1D PS structures in the above-mentioned references. However, studies based on analytical models of PS structures are still very limited. By using the perturbation method, Gao and Wang first derived the analytical formula for electrostatic potential in a bent ZnO nanowire pushed by a lateral force; however, they neglected the effect of piezoelectric field on the mechanical deformation of the ZnO nanowire [21]. That is to say, the analytical model
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