Energy harvesting efficiency in GaN nanowire-based nanogenerators: the critical influence of the Schottky nanocontact

Abstract

The performances of 1D-nanostructure based nanogenerators are governed by the ability of nanostructures to efficiently convert mechanical deformation into electrical energy, and by the efficiency with which this piezo-generated energy is harvested. In this paper, we highlight the crucial influence of the GaN nanowire-metal Schottky nanocontact on the energy harvesting efficiency. Three different metals, p-type doped diamond, PtSi and Pt/Ir, have been investigated. By using an atomic force microscope equipped with a Resiscope module, we demonstrate that the harvesting of piezo-generated energy is up to 2.4 times more efficient using a platinum-based Schottky nanocontact compared to a doped diamond-based nanocontact. In light of Schottky contact characteristics, we evidence that the conventional description of the Schottky diode cannot be applied. The contact is governed by its nanometer size. This specific behaviour induces notably a lowering of the Schottky barrier height, which gives rise to an enhanced conduction. We especially demonstrate that this effective thinning is directly correlated with the improvement of the energy harvesting efficiency, which is much pronounced for Pt-based Schottky diodes. These results constitute a building block to the overall improvement of NW-based nanogenerator devices.

High Piezoelectric Conversion Properties of Axial InGaN/GaN Nanowires

“…This electrical module is connected to the substrate (via an ohmic contact formed between the NW bottom and the substrate [ 37 ]) and to the conductive AFM tip. The used PtSi AFM tip being characterized by a work function of about 5 eV [ 38 ] and the GaN by an electron affinity of the GaN is 4.1 eV, the AFM tip/GaN NW contact forms a Schottky diode, through which are collected the piezo-generated charges [ 39 ]. In our specific AFM configuration, the topographic and the electrical signals are continuously recorded.…”

Stable and High Piezoelectric Output of GaN Nanowire-Based Lead-Free Piezoelectric Nanogenerator by Suppression of Internal Screening

“…Forming a p-n homojunction and heterojunction is an efficient route to harvest high piezoelectric output by suppressing the free carrier screening and junction screening [ 20 , 21 , 22 , 23 , 24 ]. Until now, most of the PNGs that are based on GaN NWs have been constructed using Schottky junction configuration, as in the case of resiscopy [ 25 , 26 ]. However, the performance of Schottky junction based PNGs degrades significantly due to high reverse leakage current originating from defects as metal-semiconductor interface.…”

High Piezoelectric Conversion Properties of Axial InGaN/GaN Nanowires

“…4c, where the maximum output voltages generated by the different sets of samples, as well as the measured ones for binary p-doped GaN NWs [28], have been plotted as a function of the constant normal force. The observed saturation of the generated outputs can be explained by a saturation of the internal electric field inside the NWs, resulting from the saturated rotation of electric dipoles [44], and/or by a limitation of the harvested energy through the Schottky contact, as we have recently reported [38]. In fact, as the insertion thickness increases, the piezo-generated output voltages also increase (Fig.…”

“…This evolution of the generated signals illustrates lower conversion efficiency in the case of the 35 nm-thick insertions which results from the creation of a smaller piezoelectric field in comparison with the thicker insertion, for an equivalent deformation force. We have recently demonstrated that because the AFM tip/NW contact is governed by its nanometer size, the conventional description of the Schottky diode cannot be applied [38]. In the case of Schottky nano-contact, the effective Schottky barrier height becomes a function of the diode size.…”

“…An ohmic contact is formed between the NWs bottom and the substrate[37]. Conversely, between the NW top and the AFM tip, because we use a PtSi tip characterized by a work function of about 5 eV[38] and because the electron affinity of the GaN is 4.1 eV, the PtSi-GaN contact forms a Schottky barrier that ensures the charge recuperation for piezo-Peer-reviewed version available at Nanomaterials 2018, 8, 367; doi:10.3390/nano8060367Figure 3 presents 3D mappings of output voltage peaks generated by the three sets of InGaN/GaN NW arrays recorded for constant normal force (CNF) of 100 and 200 nN. (Intermediate CNF values of 30, 60…”