Exponential size-dependent tunability of strain on the transport behavior in ZnO tunnel junctions: an ab initio study

Abstract

It is an interesting issue if the transport behavior of a piezoelectric tunnel junction is sensitive to external strain or stress, and it implies a prospect for developing novel mechanical sensors, transducers, piezotronic devices, etc. Many studies paid attention to this issue, yet how the strain and stress tunable transport behavior of a tunnel junction depends on the barrier thickness is still rarely known. Using the first principles calculations, we investigate the size-dependent and strain-tunable transport behavior in the tunnel junctions. It was confirmed that external strain has strong control over the transport properties of ZnO tunnel junctions, with several times amplification of tunnel conductance obtained by strain reversal. More importantly, the conductance amplification by strain reversal exponentially changes with the barrier thickness, indicating the size-dependent strain tunability of the transport behavior. The electrostatic quantities (i.e., built-in field, depolarization field, polarization, interfacial dipoles and potential barrier) and the transport properties of tunnel junctions were comprehensively analyzed to reveal the relationships between these quantities and their size dependence. The exponential size-dependence of strain tunable transport behavior in ZnO tunnel junctions is attributed to the linear change in the potential barrier with the barrier thickness. Our simulations provide an insight of how to maximize the strain tunability of transport behavior of piezoelectric tunnel junctions by thickness design and strain engineering.

Fundamentals and Applications of ZnO-Nanowire-Based Piezotronics and Piezo-Phototronics

“…The tunneling effect can also be altered. Simulations by Zheng et al revealed that external strain can effectively tune the transport properties of ZnO piezoelectric tunnel junctions, and the size dependence of the strain tunability exhibits a simple exponential law [ 145 ].…”

A review of recentab initiostudies on strain-tunable conductivity in tunnel junctions with piezoelectric, ferroelectric and multiferroic barriers

“…A direct and powerful control of tunnel junctions is via strain. In fact, it is a natural idea to control the tunnel conductance of PTJs via the piezoelectric effect [1,2,[42][43][44]. Since enhanced piezoelectric properties are forecast when the size of the piezoelectric material is down to the nanoscale, people are eager to control their new functionalities in novel functional nanoelectronics.…”

“…Combining the strain effect with other influencing factors such as electrodes [93,94] and size effect [42], one can gain a more comprehensive picture of the strain controllability on the performances of ZnO piezoelectric nanodevices, as reported by research based on ab initio calculations. For example, Zhu et al [42] reported size-dependent amplification of tunnel conductance through ZnO tunnel junctions by strain reversal. The ratio of tunnel conductance under 3% strain G + ( ) to that under −3% strain G ,…”

“…Zhu et al [108] recently further analyzed the band structure, transmission spectrum and coefficients of a GaN tunnel junction under −2% to 2% strain. The SBH in the central region was found to decease with strain from −2% to 2%.…”