Layer engineering piezotronic effect in two-dimensional homojunction transistors

Abstract

The semiconductor junctions based on piezoelectric materials are of great importance for the realization of functionality and versatility in sensing devices. Two-dimensional (2D) stacked materials provide a promising route to design novel semiconductor junctions due to their layer-dependent electronic and optical properties. However, the combination of layer-dependent band structure and piezoelectricity in device designs is rarely explored to date. In this work, we propose piezotronic transistors designed by layer engineering 2D homojunction. A 2D Poisson equation including the piezoelectric polarization is derived and then combined self-consistently with the non-equilibrium Green function to explore the carrier transport. We find a peculiar symmetrical modulation mechanism of piezotronic effect on carrier transport, i.e., flipping the sign of externally applied strain can drive symmetrical transport process regarding bias polarity. Additionally, the results show that the transport is a mixing of thermionic and tunneling current, which are comparable at low bias but predominated by the quantum tunneling effect at high bias. Although our 2D homojunction transistor is similar to Schottky diodes, the on/off ratio and gauge factors are higher than most of metal-semiconductor contact piezotronic devices. Moreover, for the device with symmetrical stacking configurations, increasing layer number in 2D homojunction can decrease the output current but enhance the gauge factors. By contrast, the device performance in asymmetrical stacking systems is insensitive to the variation of layer number. Our demonstration of layer engineering 2D homojunction transistor not only enriches the fundamental physics of piezotronics, but also open an avenue for designing highly sensitive strain sensors based on diverse 2D layered junctions.