压缩应变载荷下氮化镓隧道结微观压电特性及其巨压电电阻效应∗

摘要

电子器件可控性研究在日益追求器件智能化和可控化的当今社会至关重要.基于第一性原理和量子输运计算，本文研究了压缩应变载荷对氮化镓(GaN)隧道结基态电学性质和电流输运的影响，在原子尺度上窥视了氮化镓隧道结的微观压电性，验证了其内在的巨压电电阻(GPR)效应.计算结果表明，压缩应变载荷可以调节隧道结内氮化镓势垒层的电势能降、内建电场、电荷密度和极化强度，进而实现对隧道结电流输运和隧穿电阻的调控.在−1.0 V的偏置电压下，−5%的压缩应变载荷将使氮化镓隧道结的隧穿电阻增至4倍.本研究展现了氮化镓隧道结在可控电子器件中的应用潜力，也展现了应变工程在调控电子器件性能方面的光明前景.%It is an urgent and significant issue to investigate the influence factors of functional devices and then improve, modify or control their performances, which has important significance for the practical application and electronic industry. Based on first principle and quantum transport calculations, the effects of compressive strain on the current transport and relative electrical properties (such as the electrostatic potential energy, built-in electric field, charge density and polarization, etc.) in gallium nitride (GaN) tunnel junctions are investigated. It is found that there are potential energy drop, built-in electric field and spontaneous polarization in the GaN barrier of the tunnel junction due to the non-centrosymmetric structure of GaN. Furthermore, results also show that all these electrical properties can be adjusted by compressive strain. With the increase of the applied in-plane compressive strain, the piezocharge density in the GaN barrier of the tunnel junction gradually increases. Accordingly, the potential energy drop throughout the GaN barrier gradually flattens and the built-in electric field decreases. Meanwhile, the average polarization of the barrier is weakened and even reversed. These strain-dependent evolutions of the electric properties also provide an atomic level insight into the microscopic piezoelectricity of the GaN tunnel junction. In addition, it is inspiring to see that the current transport as well as the tunneling resistance of the GaN tunnel junction can be well tuned by the compressive strain. When the applied compressive strain decreases, the tunneling current of the junction increases and the tunneling resistance decreases. This strain control ability on the tunnel junction’s current and resistance becomes more powerful at large bias voltages. At a bias voltage of−1.0 V, the tunneling resistance can increase up to 4 times by a−5%compressive strain, which also reveals the intrinsic giant piezoelectric resistance effect in the GaN tunnel junction. This study exhibits the potential applications of GaN tunnel junctions in tunable electronic devices and also implies the promising prospect of strain engineering in the field of exploiting tunable devices.