Study Of Piezoelectric Semiconductor Devices Characteristic Tuned By Nonuniform Strain

In piezoelectric semiconductor materials,strain can change semiconductor characteristic,such as band gap,mobility.The piezoelectric polarization induced by strain can also affect the performance of piezoelectric semiconductor devices.Based on theoretical models of semiconductor device physics,now many theories and experiments for piezoelectric semiconductor devices under uniform strain have systematically studied,such as zinc oxide and gallium nitride piezoelectric semiconductor devices.However,under non-uniform strain conditions with strain gradients,flexoelectric polarization will be induced in piezoelectric materials and even non-piezoelectric materials due to the flexoelectric effect.It is necessary to study the impact of non-uniform strain on piezoelectric semiconductor devices.A theoretical model of piezoelectric semiconductor devices under non-uniform strain conditions is established.This dissertation studies the influence of strain gradient on the performance of piezotronic devices,establishes a theoretical model of high-performance piezotronic strain sensors,piezophototronic multijunction solar cells and piezotronic quantum harmonic oscillators,and studies the enhancement of nonuniform strain on polarization.Nonuniform strain can improve the sensitivity of strain sensors,the efficiency of solar cells,and decrease the surface electric field noise of quantum harmonic oscillators.This dissertation provides theoretical basis to improve the performance of strain sensors,photovoltaic devices,and qubit devices by strain gradient generated polarization.The work and conclusions presented in this dissertation are summarized as follows:1.The theoretical mechanism of piezoelectric semiconductor devices and flexoelectric effect was studied.Taking typical p-n junction and M-S junction as examples,the theoretical mechanism of piezoelectric semiconductor devices and flexoelectric effect was explained.strain or strain gradient induced polarization charges can control the carrier transport process.According to the flexoelectric theory,under different nonuniform strains,the analytical solution of strain and strain gradient distribution under specific stress conditions is given.This dissertation provides a theoretical guidance for the influence of non-uniform strain.2.A theoretical model of non-uniform strain tuned piezotronic devices was established.Strain gradient can increase the polarization charges within piezoelectric semiconductors.Based on physics of semiconductor device and piezoelectric constitutive equations,the strain gauge factor of piezotronics p-n junctions under nonuniform strain can reach 2500.The current of piezotronic M-S junction can increase up to 18 times under nonuniform strain.This dissertation can provide a theoretical guidance for the investigation of strain sensors.3.Theoretical models of parallel and tandem piezophototronic solar cells based on single type two-dimensional piezoelectric semiconductor material are proposed.Based on the detail balance principle,the output characteristics of the solar cell under different strains were calculated.Under the standard AM1.5G solar spectrum,the power conversion efficiency of Mo S₂ based parallel multijunction solar cells can reach 42.8%,and the power conversion efficiency of WS₂ based tandem multijunction solar cells can reach 48.1%.4.The influence of the piezoelectric potential generated by the polarization charge induced by the strain gradient inside the piezoelectric material on the motional state of the quantum harmonic oscillators was studied.Quantum harmonic oscillators can be formed by trapped ions,and the non-uniform strain generated piezoelectric potential can tune the potential distribution on the trapped well.By studying the influence of piezoelectric potential on the quantum harmonic oscillator system,the frequency of the quantum harmonic oscillator can be increased from 4MHz to 25MHz,and the surface electric field noise can be decreased by 6-15 times.This dissertation provides a theoretical basis for the investigation of high performance piezotronic quantum devices.