Piezotronic Effect in Solution-Grown p-Type ZnO Nanowires and Films

Abstract

Investigating the piezotronic effect in p-type piezoelectric semiconductor is critical for developing a complete piezotronic theory and designing/fabricating novel piezotronic applications with more complex functionality. Using a low temperature solution method, we were able to produce ultralong (up to 60 μm in length) Sb doped p-type ZnO nanowires on both rigid and flexible substrates. For the ptype nanowire field effect transistor, the on/off ratio, threshold voltage, mobility, and carrier concentration of 0.2% Sb-doped sample are found to be 10 5 , 2.1 V, 0.82 cm 2 ·V −1 ·s −1 , and 2.6 × 10 17 cm −3 , respectively, and the corresponding values for 1% Sb doped samples are 10 4 , 2.0 V, 1.24 cm 2 ·V −1 ·s −1 , and 3.8 × 10 17 cm −3 . We further investigated the universality of piezotronic effect in the as-synthesized Sb-doped p-type ZnO NWs and reported for the first time strain-gated piezotronic transistors as well as piezopotential-driven mechanical energy harvesting based on solution-grown p-type ZnO NWs. The results presented here broaden the scope of piezotronics and extend the framework for its potential applications in electronics, optoelectronics, smart MEMS/NEMS, and human-machine interfacing. KEYWORDS: p-type ZnO nanowire, piezotronic effect, piezotronics, piezo-phototronics, energy harvesting P iezoelectric semiconductors with wurtzite or zinc blend structures such as ZnO, GaN, InN, and ZnS have attracted increased attention in the burgeoning field of piezotronics and piezo-phototronics, which can be attributed to their numerous robust synthesis methods and potential for realizing novel applications by coupling their piezoelectric and semiconductor properties. 1−5 The working principle of piezotronics lies in the modulation/gating of carrier transport across the barriers/ junctions through piezoelectric-polarization-induced electric field (piezopotential) under strain, which is known as the piezotronic effect. 4,5 This provides a new mechanism for controlling charge carrier transport by mechanical strain in addition to the well-known electrically induced "field-effect". 6 A wide variety of novel applications based on the piezotronic effect have been demonstrated including strain sensors, 7 logic units, 8 memory cells, 9 electrochemical devices, 10 and tactile imaging arrays. 11 However, the aforementioned piezotronic devices were all fabricated using intrinsically n-type ZnO and few studies of piezotronics based on p-type materials, especially p-type ZnO, have been done. In order to develop a full understanding of the theory of piezotronics and enable novel applications in electronics, optoelectronics, smart MEMS/ NEMS, and human-machine interfacing, 4,11−14 it is essential to investigate the feasibility of p-type piezoelectric semiconductors for piezotronic applications.The p-type doping in ZnO nanowires (NWs) has been previously achieved through a variety of methods including chemical vapor deposition 15−17 and pulsed laser deposition. 18,19 However, the doping often suffers from poor st...

Development and progress in piezotronics

“…The first p-type piezotronic transistor was reported in 2013 [60], roughly 7 years after the discovery of piezotronics. It was made possible by successfully synthesizing Sb doped p-type ultra-long ZnO nanowires through the hydrothermal method.…”

“…Using dopants with large atomic radius such as Sb is also problematic. They distort the crystal structure of the ZnO, leading to undesired situations such as reduced growth length and degraded material flexibility [60,63]. GaN, on the other hand, has no problem of being doped into both n-type and p-type and has proven advantages in the field of optoelectronics [64,65].…”

The interplay between morphology and photocatalytic activity in ZnO and N-doped ZnO crystals

“…N could be used to obtain a stable p-type N-doped ZnO (ZnO:N) semiconductor structure [29][30][31], resulting in the improvement of photocatalytic activity [32][33][34][35][36][37][38][39][40][41]. Theoretical calculations point out that N is the best superficial acceptor candidate for ZnO [42] while Amiri et al [43] have analyzed the possible source of ferromagnetism in ZnO:N compounds by using ab-initio calculations.…”

Piezoelectric performance enhancement of ZnO flexible nanogenerator by a NiO–ZnO p–n junction formation

“…Several attempts have been previously made to address this problem by spin-coating a p-type polymer to form a p-n junction [18][19][20][21][22][23]. This greatly improved the output performance of the nanogenerator by reducing the electron screening effects.…”