Because of the coupling between semiconducting and piezoelectric properties in wurtzite materials, strain-induced piezo-charges can tune the charge transport across the interface or junction, which is referred to as the piezotronic effect. For devices whose dimension is much smaller than the mean free path of carriers (such as a single atomic layer of MoS2), ballistic transport occurs. In this study, transport in the monolayer MoS2 piezotronic transistor is studied by presenting analytical solutions for two-dimensional (2D) MoS2. Furthermore, a numerical simulation for guiding future 2D piezotronic nanodevice design is presented.

•Piezoelectric polarization of ZnO slabs increases with decreasing thickness.•Piezoelectric polarization of thick ZnO slabs is much smaller than that of bulk.•Piezoelectric-potential-induced states are responsible for the depolarization.•Piezoelectric potential has an influence on the vacancy electronic structures in ZnO.The piezoelectric polarization of ZnO (0001) thin films is calculated for varying thickness. A new depolarization mechanism based on the occupation of quantum states induced by the internal electric field is proposed to explain the asymptotical deviation of piezoelectric polarization of thin films from the bulk value. The mechanism is also related to the stability of ZnO polar surfaces. The internal electric field is also demonstrated to have important influence on the defect electronic structures of vacancy-doped ZnO thin films.

For the materials that simultaneously exhibit piezoelectric and semiconductor properties, such as wurtzite ZnO, GaN and InN, as well as two-dimensional single MoS2, piezoelectric charges induced by externally applied strain can tune/control carrier transport at a metal-semiconductor contact or semiconductor junction, which is named piezotronic effect. Metal-semiconductor-metal piezotronic transistors are key piezotronic nanodevices for electromechanical applications, and they are typical nonlinear elements. In this paper, a simplified current-voltage analysis solution of piezotronic transistors is developed, which can be used for circuit design and simulation. Furthermore, the typical nonlinear circuit: Chua’s circuit based on piezotronic transistors is simulated. We find that the output signal of the piezotronic transistor circuit can be switched and changed asymmetrically by externally applied strain. This study provides insight into the nonlinear properties of the piezotronic transistor, as well as guidance for piezotronic transistor nonlinear circuit application.

•Using the first principle calculations, the widths of piezoelectric charge distributions in an Ag-ZnO-Ag transistor are obtained, which are key parameters for understanding the piezotronic effect.•The modulations of Schottky barriers at two transistor interfaces show asymmetric behavior due to piezotronic effect, which agrees with previous experiment results.Piezoelectric semiconductors, such as wurtzite structured ZnO, GaN, and InN, have novel properties owing to piezoelectric polarization tuned/controlled electronic transport characteristics. Under an externally applied strain, piezoelectric charges are created at an interface or junction, which are likely to tune and modulate the local band structure. Taking an Ag-ZnO-Ag two-terminal piezotronic transistor as an example, strain-dependent piezoelectric charge distributions and modulation of Schottky barrier heights (SBHs) at metal/semiconductor interfaces have been investigated by the first principle simulations. The width of piezocharge distribution is calculated by the density function theory and the Poisson equation. The modulations of SBHs at two interfaces show opposite trend under the applied strain. This study not only provides an understanding about the piezotronic effect from quantum theory point of view, but also a new method to calculate the key parameter for optimizing the design of piezotronic devices.

•The piezoelectric field is created by applying strain on ZnO nanowires. Under UV illumination, the photo-generated electrons and holes will be separated under the driving of piezoelectric field.•The photocatalytic activity of ZnO nanowires for degrading methylene blue has been greatly enhanced by the piezoelectric-driven separation of photo-generated carriers.•A new fundamental mechanism that couples the piezoelectric and photocatalytic properties of ZnO nanowires for the degradation of organic dye has been demonstrated.Piezoelectric semiconductors, such as wurtzite structure ZnO, GaN, and InN, have novel properties of coupling of piezoelectric and semiconductor. The piezoelectric field is created inside ZnO nanowires by applying strain. The photo-generated electrons and holes will be separated under the driving of piezoelectric field. The photocatalytic activity of ZnO nanowires for degrading methylene blue has been enhanced by the piezoelectric-driven separation of photo-generated carriers. Coupling the piezoelectric and photocatalytic properties of ZnO nanowires, a new fundamental mechanism for the degradation of organic dye has been demonstrated.A new fundamental mechanism that couples the piezoelectric and photocatalytic properties of ZnO nanowires for the degradation of organic dye has been demonstrated. The photocatalytic activity of ZnO nanowires for degrading methylene blue has been greatly enhanced by the piezoelectric-driven separation of photo-generated carriers.

Self-powered chaos signal generator is potentially useful in future medical system, such as low cost portable human healthy monitor and treatment without external power source. For both functional and power unit, the power level of electric energy generator and consumption is a key factor for self-powered system. In this paper, we have investigated the power consumption of three typical output modes of a simple chaos circuit. Analytical analysis for power consumption of fixed output mode is obtained for evaluating the power characteristics of chaos signal generator. Numerical calculations are given for predicting the power characteristics of periodical and chaotic output modes. This study is important for not only understanding the power consumption of chaos signal generator, but also guiding new self-powered chaos signal generator design.