Piezoelectric potential in vertically aligned nanowires for high output nanogenerators

Romano, Giuseppe; Mantini, G.; Carlo, Aldo Di; D’Amico, A.; Falconi, Christian; Wang, Zhong Lin

doi:10.1088/0957-4484/22/46/465401

Cited by 169 publications

(140 citation statements)

References 25 publications

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“…This is the only difference with results obtained in the case of a pure cylindrical NW surrounded by air, which has shown no effect of NW geometry once the nanowire was longer than the depletion region thickness which was, in that case, induced by a Schottky barrier at the top of the nanowire. [20] Indeed, in our case, the strain distribution within the NG composite was not uniform. As NW radius decreased, a larger strain was transferred from the soft matrix and top insulating layer to the top corner of the NW, resulting in a larger polarization in the depleted zone, which actually contributed to the piezopotential increase.…”

Section: Geometry Effects Of Nw Length and Radiusmentioning

confidence: 51%

“…A few papers have accounted for free carriers, although without account for SFLP. [20,37] Here instead, full coupling between piezoelectric effect and semiconducting physics, including free carriers and SFLP, was considered.ZnO nanowires (NWs) are excellent candidates for the integration of energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. However, ZnO NWs are usually nonintentionally n-doped during their growth.…”

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confidence: 99%

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confidence: 99%

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Unveiling the Influence of Surface Fermi Level Pinning on the Piezoelectric Response of Semiconducting Nanowires

Tao

Mouis

Ardila

2017

Adv Elect Materials

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environment ever since they were first demonstrated. [4] Experimentally, it has been proved that ZnO NW based piezoelectric devices can generate a potential of a few volts. [15] This can be retrieved theoretically as long as there are no free carriers. However, experimentally prepared ZnO NWs are spontaneously n-type doped by impurities during their synthesis [16,17] and in such a case, screening by free carriers is expected to reduce drastically the piezoelectric response. There remain many such contradictions between experimental results and the present theoretical understanding of ZnO NW-based devices when realistic doping levels are considered. Chief among them are (1) decent and length-dependent performance of ZnO NWs, [18] while anticipations based on analytical and computational study showed that the output of NWs under compression were reduced to a few millivolts and presenting length-independent performance due to the screening effect; [19,20] (2) enhanced piezoelectric coefficients, [21] which were measured for ZnO NWs with diameter beyond the size effects anticipated by ab initio method; [22] and (3) dissymmetric piezoelectric response of bent nanogenerators (NGs) under tensile and compressive strain. [23] Relatively high potentials (>0.2 V) can be repeatedly obtained from NGs integrating long and large ZnO NWs [24][25][26][27] with presumably nonintentional doping. Increasing the doping concentration will reduce the generated piezopotential. [28] The nature of matrix material, as well as processing conditions, has been shown to play an important role. [24] (Table S1, Supporting Information).In this paper, we solve these contradictions by accounting for surface Fermi level pinning (SFLP). This effect commonly exists at the surface of III-V and II-VI semiconductor compounds. [29][30][31] At the surface of n-type ZnO NWs, oxygen molecules get negatively charged by capturing the free electrons from NW core. This forms a low-conductivity depletion layer near the surface, where the screening of piezoelectric potential by free carriers effect is suppressed. [30,[32][33][34][35][36] This effect has been used to neglect free carriers in most simulation studies dealing with the piezoelectric response of semiconducting nanowirebased devices. A few papers have accounted for free carriers, although without account for SFLP. [20,37] Here instead, full coupling between piezoelectric effect and semiconducting physics, including free carriers and SFLP, was considered.ZnO nanowires (NWs) are excellent candidates for the integration of energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. However, ZnO NWs are usually nonintentionally n-doped during their growth. Thus, it can be expected theoretically that their piezoelectric response be degraded and mostly geometry-independent as a result of strong screening effects by free carriers, while experimentally many NW-based piezoelectric transducers demonstrate quite reasonable performance. In this paper, this apparent contradiction is explained by...

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Section: Geometry Effects Of Nw Length and Radiusmentioning

confidence: 51%

mentioning

confidence: 99%

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Unveiling the Influence of Surface Fermi Level Pinning on the Piezoelectric Response of Semiconducting Nanowires

Tao

Mouis

Ardila

2017

Adv Elect Materials

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“…8e, f show that the space of the patterned ZnO NAs is larger than that of the pristine ZnO NAs. When a compressive strain is applied on the ZnO NAs, positive and negative potentials are produced at the stretched and compressed sides, respectively [159]. The electrons then flow from the ZnO NAs to the electrode.…”

Section: Nanogenerator Devicesmentioning

confidence: 99%

Design and tailoring of patterned ZnO nanostructures for energy conversion applications

Kang

Liao

et al. 2017

Sci. China Mater.

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ZnO is a typical direct wide-bandgap semiconductor material, which has various morphologies and unique physical and chemical properties, and is widely used in the fields of energy, information technology, biomedicine, and others. The precise design and controllable fabrication of nanostructures have gradually become important avenues to further enhancing the performance of ZnO-based functional nanodevices. This paper introduces the continuous development of patterning technologies, provides a comprehensive review of the optical lithography and laser interference lithography techniques for the controllable fabrication of ZnO nanostructures, and elaborates on the potential applications of such patterned ZnO nanostructures in solar energy, water splitting, light emission devices, and nanogenerators. Patterned ZnO nanostructures with highly controllable morphology and structure possess discrete three-dimensional space structure, enlarged surface area, and improved light capture ability, which realize the efficient carrier regulation, achieve highly efficient energy conversion, and meet the diverse requirements of functional nanodevices. The patterning techniques proposed for the precise design of ZnO nanostructures not only have important guiding significance for the controllable fabrication of complex nanostructures of other materials, but also open up a new route for the further development of functional nanostructures.

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“…Consequently, the intrinsic piezopotential differences generated through the ZnO NRs are canceled either partially or completely, leading directly to NG output performance reduction; this is referred to as the screening effect. [23][24][25] This effect must therefore be suppressed much more effectively by modulation of the free carrier density in the ZnO bulk for improved device performance.…”

Section: à3mentioning

confidence: 99%

High-efficiency micro-energy generation based on free-carrier-modulated ZnO:N piezoelectric thin films

Lee

Park

Yim

et al. 2014

Applied Physics Letters

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The free-carrier-modulated ZnO:N thin film-based flexible nanogenerators (NZTF-FNGs) are proposed and experimentally demonstrated. The suggested flexible nanogenerators (FNGs) are fabricated using N-doped ZnO thin films (NZTFs) as their piezoelectric active elements, which are deposited by a radio frequency magnetron sputtering technique with an N2O reactive gas as an in situ dopant source. Considerable numbers of N atoms are uniformly incorporated into NZTFs overall during their growth, which would enable them to significantly compensate the unintentional background free electron carriers both in the bulk and at the surface of ZnO thin films (ZTFs). This N-doping approach is found to remarkably enhance the performance of NZTF-FNGs, which shows output voltages that are almost two orders of magnitude higher than those of the conventionally grown ZnO thin film-based FNGs. This is believed to be a result of both substantial screening effect suppression in the ZTF bulk and more reliable Schottky barrier formation at the ZTF interfaces, which is all mainly caused by the N-compensatory doping process. Furthermore, the NZTF-FNGs fabricated are verified via charging tests to be suitable for micro-energy harvesting devices.

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Piezoelectric potential in vertically aligned nanowires for high output nanogenerators

Cited by 169 publications

References 25 publications

Unveiling the Influence of Surface Fermi Level Pinning on the Piezoelectric Response of Semiconducting Nanowires

Unveiling the Influence of Surface Fermi Level Pinning on the Piezoelectric Response of Semiconducting Nanowires

Design and tailoring of patterned ZnO nanostructures for energy conversion applications

High-efficiency micro-energy generation based on free-carrier-modulated ZnO:N piezoelectric thin films

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