Ultrasensitive Strain Sensor Based on a Tunnel Junction with an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mi>Al</mml:mi><mml:mi mathvariant="normal">N</mml:mi></mml:mrow><mml:mo>/</mml:mo><mml:mrow><mml:mi>Ga</mml:mi><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math> Core-Shell Nanowire

Piezotronic transistor operating in the quantum tunneling regime has recently roused wide interest for developing ultrasensitive strain sensing with applications in wearable electronics and human-machine interfaces. However, the lack of a strict theoretical demonstration from a quantum perspective renders the development of such an emerging area particularly slow due to their complex fabrication process and vulnerable experimental interference. Here, by combining third-dimensional self-consistent calculation with a nonequilibrium Green's function framework, we study the intrinsic device properties of piezotronic tunneling transistor (PTT) based on $\mathrm{Al}\mathrm{N}/\mathrm{Ga}\mathrm{N}$ core-shell nanowire. The results show that strain-induced piezoelectric polarization can remarkably tune tunneling barrier height and width, both of which are increased by tensile strain and decreased by compressive strain. At a moderate strain amplitude of 1.0% and bias of 2.0 V, the strain-induced change in effective barrier height and width can reach as high as 0.5 eV and 4.0 nm, respectively. This remarkable tunability in the barrier allows for an ultrahigh on/off current ratio ${10}^{17}$, and giant gauge factor 1.2 \ifmmode\times\else\texttimes\fi{} ${10}^{8}$ in current and 1.1 \ifmmode\times\else\texttimes\fi{} ${10}^{13}$ in resistance. The performance can be further optimized by properly tailoring device architectures, including insulator thickness, nanowire length, or core-shell size. Our demonstration of the PTT with combined quantum tunneling and piezotronic effect opens a window for designing highly sensitive, large on/off ratio and low-power strain sensing.